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Common Hooks

GitHub stars npm version Changelog

$ npm install feathers-hooks-common --save

feathers-hooks-common is a collection of common hooks and utilities.

Authentication hooks are documented separately.

Note: Many hooks are just a few lines of code to implement from scratch. If you can't find a hook here but are unsure how to implement it or have an idea for a generally useful hook create a new issue here.

client

client(... whitelist) source

A hook for passing params from the client to the server.

  • Used as a before hook.

ProTip Use the paramsFromClient hook instead. It does exactly the same thing as client but is less likely to be deprecated.

Only the hook.params.query object is transferred to the server from a Feathers client, for security among other reasons. However if you can include a hook.params.query.$client object, e.g.

service.find({
  query: {
    dept: 'a',
    $client: {
      populate: 'po-1',
      serialize: 'po-mgr'
    }
  }
});

the client hook will move that data to hook.params on the server.

service.before({ all: [ client('populate', 'serialize', 'otherProp'), myHook ]});
// myHook's hook.params will be
// { query: { dept: 'a' }, populate: 'po-1', serialize: 'po-mgr' } }

Options:

  • whitelist (optional) Names of the potential props to transfer from query.client. Other props are ignored. This is a security feature.

ProTip You can use the same technique for service calls made on the server.

See Util: paramsForServer and paramsFromClient.

combine

combine(... hookFuncs) source

Sequentially execute multiple hooks within a custom hook function.

function (hook) { // an arrow func cannot be used because we need 'this'
  // ...
  hooks.combine(hook1, hook2, hook3).call(this, hook)
    .then(hook => {});
}

Options:

  • hooks (optional) - The hooks to run.

ProTip: combine is primarily intended to be used within your custom hooks, not when registering hooks.. Its more convenient to use the following when registering hooks:

const workflow = [hook1(), hook2(), ...];
app.service(...).hooks({
  before: {
    update: [...workflow],
    patch: [...workflow],
  },
});

debug

debug(label) source

Display current info about the hook to console.

  • Used as a before or after hook.
const { debug } = require('feathers-hooks-common');

debug('step 1')
// * step 1
// type: before, method: create
// data: { name: 'Joe Doe' }
// query: { sex: 'm' }
// result: { assigned: true }

Options:

  • label (optional) - Label to identify the debug listing.

dePopulate

dePopulate() source

Removes joined and computed properties, as well any profile information. Populated and serialized items may, after dePopulate, be used in service.patch(id, items) calls.

  • Used as a before or after hook on any service method.
  • Supports multiple result items, including paginated find.
  • Supports an array of keys in field.

See also populate, serialize.

disallow

disallow(...providers) source

Disallows access to a service method completely or for specific providers. All providers (REST, Socket.io and Primus) set the hook.params.provider property, and disallow checks this.

  • Used as a before hook.
app.service('users').before({
  // Users can not be created by external access
  create: hooks.disallow('external'),
  // A user can not be deleted through the REST provider
  remove: hooks.disallow('rest'),
  // disallow calling `update` completely (e.g. to allow only `patch`)
  update: hooks.disallow(),
  // disallow the remove hook if the user is not an admin
  remove: hooks.when(hook => !hook.params.user.isAdmin, hooks.disallow())
});

ProTip Service methods that are not implemented do not need to be disallowed.

Options:

  • providers (optional, default: disallows everything) - The transports that you want to disallow this service method for. Options are:
    • socketio - will disallow the method for the Socket.IO provider
    • primus - will disallow the method for the Primus provider
    • rest - will disallow the method for the REST provider
    • external - will disallow access from all providers other than the server.
    • server - will disallow access for the server

disableMultiItemChange

disableMultiItemChange() source

Disables update, patch and remove methods from using null as an id, e.g. remove(null). A null id affects all the items in the DB, so accidentally using it may have undesirable results.

  • Used as a before hook.
app.service('users').before({
  update: hooks.disableMultiItemChange(),
});

discard

discard(... fieldNames) source

Delete the given fields either from the data submitted or from the result. If the data is an array or a paginated find result the hook will Delete the field(s) for every item.

  • Used as a before hook for create, update or patch.
  • Used as an after hook.
  • Field names support dot notation e.g. name.address.city.
  • Supports multiple data items, including paginated find.
const { discard } = require('feathers-hooks-common');

// Delete the hashed `password` and `salt` field after all method calls
app.service('users').after(discard('password', 'salt'));

// Delete _id for `create`, `update` and `patch`
app.service('users').before({
  create: discard('_id', 'password'),
  update: discard('_id'),
  patch: discard('_id')
})

ProTip: This hook will always delete the fields, unlike the remove hook which only deletes the fields if the service call was made by a client.

ProTip: You can replace remove('name') with iff(isProvider('external'), discard('name)). The latter does not contains any hidden "magic".

Options:

  • fieldNames (required) - One or more fields you want to remove from the object(s).

See also remove.

else

iff(...).else(...hookFuncs) source

iff().else() is similar to iff and iffElse. Its syntax is more suitable for writing nested conditional hooks. If the predicate in the iff() is falsey, run the hooks in else() sequentially.

  • Used as a before or after hook.
  • Hooks to run may be sync, Promises or callbacks.
  • feathers-hooks catches any errors thrown in the predicate or hook.
service.before({
  create:
    hooks.iff(isProvider('server'),
      hookA,
      hooks.iff(isProvider('rest'), hook1, hook2, hook3)
        .else(hook4, hook5),
      hookB
    )
      .else(
        hooks.iff(hook => hook.path === 'users', hook6, hook7)
      )
});

or:

service.before({
  create:
    hooks.iff(isServer, [
      hookA,
      hooks.iff(isProvider('rest'), [hook1, hook2, hook3])
        .else([hook4, hook5]),
      hookB
    ])
      .else([
        hooks.iff(hook => hook.path === 'users', [hook6, hook7])
      ])
});

Options:

  • hookFuncs (optional) - Zero or more hook functions. They may include other conditional hooks. Or you can use an array of hook functions as the second parameter.

See also iff, iffElse, when, unless, isNot, isProvider.

This The predicate and hook functions in the if, else and iffElse hooks will not be called with this set to the service. Use hook.service instead.

every

every(... hookFuncs) source

Run hook functions in parallel. Return true if every hook function returned a truthy value.

  • Used as a predicate function with conditional hooks.
  • The current hook is passed to all the hook functions, and they are run in parallel.
  • Hooks to run may be sync or Promises only.
  • feathers-hooks catches any errors thrown in the predicate.
service.before({
  create: hooks.iff(hooks.every(hook1, hook2, ...), hookA, hookB, ...)
});
hooks.every(hook1, hook2, ...).call(this, currentHook)
  .then(bool => { ... });

Options:

  • hookFuncs (required) Functions which take the current hook as a param and return a boolean result.

See also some.

iff

iff(predicate: boolean|Promise|function, ...hookFuncs: HookFunc[]): HookFunc source

Resolve the predicate to a boolean. Run the hooks sequentially if the result is truthy.

  • Used as a before or after hook.
  • Predicate may be a sync or async function.
  • Hooks to run may be sync, Promises or callbacks.
  • feathers-hooks catches any errors thrown in the predicate or hook.
const { iff, populate } = require('feathers-hooks-common');
const isNotAdmin = adminRole => hook => hook.params.user.roles.indexOf(adminRole || 'admin') === -1;

app.service('workOrders').after({
  // async predicate and hook
  create: iff(
    () => new Promise((resolve, reject) => { ... }),
    populate('user', { field: 'authorisedByUserId', service: 'users' })
  )
});

app.service('workOrders').after({
  // sync predicate and hook
  find: [ iff(isNotAdmin(), hooks.remove('budget')) ]
});

or with the array syntax:

app.service('workOrders').after({
  find: [ iff(isNotAdmin(), [hooks.remove('budget'), hooks.remove('password')]
});

Options:

  • predicate (required) - Determines if hookFuncs should be run or not. If a function, predicate is called with the hook as its param. It returns either a boolean or a Promise that evaluates to a boolean
  • hookFuncs (optional) - Zero or more hook functions. They may include other conditional hooks. Or you can use an array of hook functions as the second parameter.

See also iffElse, else, when, unless, isNot, isProvider.

This The predicate and hook functions in the if, else and iffElse hooks will not be called with this set to the service. Use hook.service instead.

iffElse

iffElse(predicate, trueHooks, falseHooks) source

Resolve the predicate to a boolean. Run the first set of hooks sequentially if the result is truthy, the second set otherwise.

  • Used as a before or after hook.
  • Predicate may be a sync or async function.
  • Hooks to run may be sync, Promises or callbacks.
  • feathers-hooks catches any errors thrown in the predicate or hook.
const { iffElse, populate, serialize } = require('feathers-hooks-common');
app.service('purchaseOrders').after({
  create: iffElse(() => { ... },
    [populate(poAccting), serialize( ... )],
    [populate(poReceiving), serialize( ... )]
  )
});

Options:

  • predicate (required) - Determines if hookFuncs should be run or not. If a function, predicate is called with the hook as its param. It returns either a boolean or a Promise that evaluates to a boolean
  • trueHooks (optional) - Zero or more hook functions run when predicate is truthy.
  • falseHooks (optional) - Zero or more hook functions run when predicate is false.

See also iff, else, when, unless, isNot, isProvider.

This The predicate and hook functions in the if, else and iffElse hooks will not be called with this set to the service. Use hook.service instead.

isNot

isNot(predicate) source

Negate the predicate.

  • Used as a predicate with conditional hooks.
  • Predicate may be a sync or async function.
  • feathers-hooks catches any errors thrown in the predicate.
import hooks, { iff, isNot, isProvider } from 'feathers-hooks-common';
const isRequestor = () => hook => new Promise(resolve, reject) => ... );

app.service('workOrders').after({
  iff(isNot(isRequestor()), hooks.remove( ... ))
});

Options:

  • predicate (required) - A function which returns either a boolean or a Promise that resolves to a boolean.

See also iff, iffElse, else, when, unless, isProvider.

isProvider

isProvider(provider) source

Check which transport called the service method. All providers (REST, Socket.io and Primus) set the params.provider property which is what isProvider checks for.

  • Used as a predicate function with conditional hooks.
import { iff, isProvider, remove } from 'feathers-hooks-common';

app.service('users').after({
  iff(isProvider('external'), remove( ... ))
});

Options:

  • provider (required) - The transport that you want this hook to run for. Options are:
    • server - Run the hook if the server called the service method.
    • external - Run the hook if any transport other than the server called the service method.
    • socketio - Run the hook if the Socket.IO provider called the service method.
    • primus - If the Primus provider.
    • rest - If the REST provider.
  • providers (optional) - Other transports that you want this hook to run for.

See also iff, iffElse, else, when, unless, isNot, isProvider.

lowerCase

lowerCase(... fieldNames) source

Lower cases the given fields either in the data submitted or in the result. If the data is an array or a paginated find result the hook will lowercase the field(s) for every item.

  • Used as a before hook for create, update or patch.
  • Used as an after hook.
  • Field names support dot notation.
  • Supports multiple data items, including paginated find.
const { lowerCase } = require('feathers-hooks-common');

// lowercase the `email` and `password` field before a user is created
app.service('users').before({
  create: lowerCase('email', 'username')
});

Options:

  • fieldNames (required) - One or more fields that you want to lowercase from the retrieved object(s).

See also upperCase.

paramsFromClient

paramsFromClient(... whitelist) source

A hook, on the server, for passing params from the client to the server.

  • Used as a before hook.
  • Companion to the client utility function paramsForServer.

By default, only the hook.params.query object is transferred to the server from a Feathers client, for security among other reasons. However you can explicitly transfer other params props with the client utility function paramsForServer in conjunction with the hook function paramsFromClient on the server.

// client
import { paramsForServer } from 'feathers-hooks-common';
service.patch(null, data, paramsForServer({
  query: { dept: 'a' }, populate: 'po-1', serialize: 'po-mgr'
}));

// server
const { paramsFromClient } = require('feathers-hooks-common');
service.before({ all: [
  paramsFromClient('populate', 'serialize', 'otherProp'), myHook
]});

// hook.params will now be
// { query: { dept: 'a' }, populate: 'po-1', serialize: 'po-mgr' } }

Options:

  • whitelist (optional) Names of the permitted props; other props are ignored. This is a security feature.

ProTip You can use the same technique for service calls made on the server.

See util: paramsForServer.

pluck

pluck(... fieldNames) source

Discard all other fields except for the provided fields either from the data submitted or from the result. If the data is an array or a paginated find result the hook will remove the field(s) for every item.

  • Used as a before hook for create, update or patch.
  • Used as an after hook.
  • Field names support dot notation.
  • Supports multiple data items, including paginated find.
const { pluck } = require('feathers-hooks-common');

// Only retain the hashed `password` and `salt` field after all method calls
app.service('users').after(pluck('password', 'salt'));

// Only keep the _id for `create`, `update` and `patch`
app.service('users').before({
  create: pluck('_id'),
  update: pluck('_id'),
  patch: pluck('_id')
})

ProTip: This hook will only fire when params.provider has a value, i.e. when it is an external request over REST or Sockets.

Options:

  • fieldNames (required) - One or more fields that you want to retain from the object(s).

All other fields will be discarded.

pluckQuery

pluckQuery(... fieldNames) source

Discard all other fields except for the given fields from the query params.

  • Used as a before hook.
  • Field names support dot notation.
  • Supports multiple data items, including paginated find.
const { pluckQuery } = require('feathers-hooks-common');

// Discard all other fields except for _id from the query
// for all service methods
app.service('users').before({
  all: pluckQuery('_id')
});

ProTip: This hook will only fire when params.provider has a value, i.e. when it is an external request over REST or Sockets.

Options:

  • fieldNames (optional) - The fields that you want to retain from the query object. All other fields will be discarded.

populate

populate(options: Object): HookFunc source

Populates items recursively to any depth. Supports 1:1, 1:n and n:1 relationships.

  • Used as a before or after hook on any service method.
  • Supports multiple result items, including paginated find.
  • Permissions control what a user may see.
  • Provides performance profile information.
  • Backward compatible with the old FeathersJS populate hook.

Examples

  • 1:1 relationship
// users like { _id: '111', name: 'John', roleId: '555' }
// roles like { _id: '555', permissions: ['foo', bar'] }
import { populate } from 'feathers-hooks-common';

const userRoleSchema = {
  include: {
    service: 'roles',
    nameAs: 'role',
    parentField: 'roleId',
    childField: '_id'
  }
};

app.service('users').hooks({
  after: {
    all: populate({ schema: userRoleSchema })
  }
});

// result like
// { _id: '111', name: 'John', roleId: '555',
//   role: { _id: '555', permissions: ['foo', bar'] } }
  • 1:n relationship
// users like { _id: '111', name: 'John', roleIds: ['555', '666'] }
// roles like { _id: '555', permissions: ['foo', 'bar'] }
const userRolesSchema = {
  include: {
    service: 'roles',
    nameAs: 'roles',
    parentField: 'roleIds',
    childField: '_id'
  }
};

usersService.hooks({
  after: {
    all: populate({ schema: userRolesSchema })
  }
});

// result like
// { _id: '111', name: 'John', roleIds: ['555', '666'], roles: [
//   { _id: '555', permissions: ['foo', 'bar'] }
//   { _id: '666', permissions: ['fiz', 'buz'] }
// ]}
  • n:1 relationship
// posts like { _id: '111', body: '...' }
// comments like { _id: '555', text: '...', postId: '111' }
const postCommentsSchema = {
  include: {
    service: 'comments',
    nameAs: 'comments',
    parentField: '_id',
    childField: 'postId'
  }
};

postService.hooks({
  after: {
    all: populate({ schema: postCommentsSchema })
  }
});

// result like
// { _id: '111', body: '...' }, comments: [
//   { _id: '555', text: '...', postId: '111' }
//   { _id: '666', text: '...', postId: '111' }
// ]}
  • Multiple and recursive includes
const schema = {
  service: '...',
  permissions: '...',
  include: [
    {
      service: 'users',
      nameAs: 'authorItem',
      parentField: 'author',
      childField: 'id',
      include: [ ... ],
    },
    {
      service: 'comments',
      parentField: 'id',
      childField: 'postId',
      query: {
        $limit: 5,
        $select: ['title', 'content', 'postId'],
        $sort: {createdAt: -1}
      },
      select: (hook, parent, depth) => ({ $limit: 6 }),
      asArray: true,
      provider: undefined,
    },
    {
      service: 'users',
      permissions: '...',
      nameAs: 'readers',
      parentField: 'readers',
      childField: 'id'
    }
  ],
};

module.exports.after = {
  all: populate({ schema, checkPermissions, profile: true })
};
  • Flexible relationship, similar to the n:1 relationship example above
// posts like { _id: '111', body: '...' }
// comments like { _id: '555', text: '...', postId: '111' }
const postCommentsSchema = {
  include: {
    service: 'comments',
    nameAs: 'comments',
    select: (hook, parentItem) => ({ postId: parentItem._id }),
  }
};

postService.hooks({
  after: {
    all: populate({ schema: postCommentsSchema })
  }
});

// result like
// { _id: '111', body: '...' }, comments: [
//   { _id: '555', text: '...', postId: '111' }
//   { _id: '666', text: '...', postId: '111' }
// ]}

Options

  • schema (required, object or function) How to populate the items. Details are below.
    • Function signature (hook: Hook, options: Object): Object
    • hook The hook.
    • options The options passed to the populate hook.
  • checkPermissions [optional, default () => true] Function to check if the user is allowed to perform this populate, or include this type of item. Called whenever a permissions property is found.
    • Function signature (hook: Hook, service: string, permissions: any, depth: number): boolean
    • hook The hook.
    • service The name of the service being included, e.g. users, messages.
    • permissions The value of the permissions property.
    • depth How deep the include is in the schema. Top of schema is 0.
    • Return truesy to allow the include.
  • profile [optional, default false] If true, the populated result is to contain a performance profile. Must be true, truesy is insufficient.

Schema

The data currently in the hook will be populated according to the schema. The schema starts with:

const schema = {
  service: '...',
  permissions: '...',
  include: [ ... ]
};
  • service (optional) The name of the service this schema is to be used with. This can be used to prevent a schema designed to populate 'blog' items from being incorrectly used with comment items.
  • permissions (optional, any type of value) Who is allowed to perform this populate. See checkPermissions above.
  • include (optional) Which services to join to the data.
Include

The include array has an element for each service to join. They each may have:

{ service: 'comments',
  nameAs: 'commentItems',
  permissions: '...',
  parentField: 'id',
  childField: 'postId',
  query: {
    $limit: 5,
    $select: ['title', 'content', 'postId'],
    $sort: {createdAt: -1}
  },
  select: (hook, parent, depth) => ({ $limit: 6 }),
  asArray: true,
  paginate: false,
  provider: undefined,
  useInnerPopulate: false,
  include: [ ... ]
}

ProTip Instead of setting include to a 1-element array, you can set it to the include object itself, e.g. include: { service: ..., nameAs: ..., ... }.

  • service [required, string] The name of the service providing the items.
  • nameAs [optional, string, default is service] Where to place the items from the join. Dot notation is allowed.
  • permissions [optional, any type of value] Who is allowed to perform this join. See checkPermissions above.
  • parentField [required if neither query nor select, string] The name of the field in the parent item for the relation. Dot notation is allowed.
  • childField [required if neither query nor select, string] The name of the field in the child item for the relation. Dot notation is allowed and will result in a query like { 'name.first': 'John' } which is not suitable for all DBs. You may use query or select to create a query suitable for your DB.
  • query [optional, object] An object to inject into the query in service.find({ query: { ... } }).
  • select [optional, function] A function whose result is injected into the query.
    • Function signature (hook: Hook, parentItem: Object, depth: number): Object
    • hook The hook.
    • parentItem The parent item to which we are joining.
    • depth How deep the include is in the schema. Top of schema is 0.
  • asArray [optional, boolean, default false] Force a single joined item to be stored as an array.
  • paginate {optional, boolean or number, default false] Controls pagination for this service.
    • false No pagination. The default.
    • true Use the configuration provided when the service was configured/
    • A number. The maximum number of items to include.
  • provider [optional] find calls are made to obtain the items to be joined. These, by default, are initialized to look like they were made by the same provider as that getting the base record. So when populating the result of a call made via socketio, all the join calls will look like they were made via socketio. Alternative you can set provider: undefined and the calls for that join will look like they were made by the server. The hooks on the service may behave differently in different situations.
  • useInnerPopulate [optional] Populate, when including records from a child service, ignores any populate hooks defined for that child service. The useInnerPopulate option will run those populate hooks. This allows the populate for a base record to include child records containing their own immediate child records, without the populate for the base record knowing what those grandchildren populates are.
  • include [optional] The new items may themselves include other items. The includes are recursive.

Populate forms the query [childField]: parentItem[parentField] when the parent value is not an array. This will include all child items having that value.

Populate forms the query [childField]: { $in: parentItem[parentField] } when the parent value is an array. This will include all child items having any of those values.

A populate hook for, say, posts may include items from users. Should the users hooks also include a populate, that users populate hook will not be run for includes arising from posts.

ProTip The populate interface only allows you to directly manipulate hook.params.query. You can manipulate the rest of hook.params by using the client hook, along with something like query: { ..., $client: { paramsProp1: ..., paramsProp2: ... } }.

Added properties

Some additional properties are added to populated items. The result may look like:

{ ...
  _include: [ 'post' ],
  _elapsed: { post: 487947, total: 527118 },
  post:
    { ...
      _include: [ 'authorItem', 'commentsInfo', 'readersInfo' ],
      _elapsed: { authorItem: 321973, commentsInfo: 469375, readersInfo: 479874, total: 487947 },
      _computed: [ 'averageStars', 'views' ],
      authorItem: { ... },
      commentsInfo: [ { ... }, { ... } ],
      readersInfo: [ { ... }, { ... } ]
} }
  • _include The property names containing joined items.
  • _elapsed The elapsed time in nano-seconds (where 1,000,000 ns === 1 ms) taken to perform each include, as well as the total taken for them all. This delay is mostly attributed to your DB.
  • _computed The property names containing values computed by the serialize hook.

The depopulate hook uses these fields to remove all joined and computed values. This allows you to then service.patch() the item in the hook.

Joining without using related fields

Populate can join child records to a parent record using the related columns parentField and childField. However populate's query and select options may be used to related the records without needing to use the related columns. This is a more flexible, non-SQL-like way of relating records. It easily supports dynamic, run-time schemas since the select option may be a function.

Populate examples

Selecting schema based on UI needs

Consider a Purchase Order item. An Accounting oriented UI will likely want to populate the PO with Invoice items. A Receiving oriented UI will likely want to populate with Receiving Slips.

Using a function for schema allows you to select an appropriate schema based on the need. The following example shows how the client can ask for the type of schema it needs.

// on client
import { paramsForServer } from 'feathers-hooks-common';
purchaseOrders.get(id, paramsForServer({ schema: 'po-acct' })); // pass schema name to server
// or
purchaseOrders.get(id, paramsForServer({ schema: 'po-rec' }));
// on server
import { paramsFromClient } from 'feathers-hooks-common';
const poSchemas = {
  'po-acct': /* populate schema for Accounting oriented PO e.g. { include: ... } */,
  'po-rec': /* populate schema for Receiving oriented PO */
};

purchaseOrders.before({
  all: paramsfromClient('schema')
});

purchaseOrders.after({
  all: populate({ schema: hook => poSchemas[hook.params.schema] }),
});
Using permissions

For a simplistic example, assume hook.params.users.permissions is an array of the service names the user may use, e.g. ['invoices', 'billings']. These can be used to control which types of items the user can see.

The following populate will only be performed for users whose user.permissions contains 'invoices'.

const schema = {
  include: [
    {
      service: 'invoices',
      permissions: 'invoices',
      ...
    }
  ]
};

purchaseOrders.after({
  all: populate(schema, (hook, service, permissions) => hook.params.user.permissions.includes(service))
});

See also dePopulate, serialize.

preventChanges

preventChanges(... fieldNames) source

Prevents the specified fields from being patched.

  • Used as a before hook for patch.
  • Field names support dot notation e.g. name.address.city.
const { preventChanges } = require('feathers-hooks-common');

app.service('users').before({
  patch: preventChanges('security.badge')
})

Options:

  • fieldNames (required) - One or more fields which may not be patched.

Consider using validateSchema if you would rather specify which fields are allowed to change.

remove

remove(... fieldNames) source

Remove the given fields either from the data submitted or from the result. If the data is an array or a paginated find result the hook will remove the field(s) for every item.

  • Used as a before hook for create, update or patch.
  • Used as an after hook.
  • Field names support dot notation e.g. name.address.city.
  • Supports multiple data items, including paginated find.
const { remove } = require('feathers-hooks-common');

// Remove the hashed `password` and `salt` field after all method calls
app.service('users').after(remove('password', 'salt'));

// Remove _id for `create`, `update` and `patch`
app.service('users').before({
  create: remove('_id', 'password'),
  update: remove('_id'),
  patch: remove('_id')
})

ProTip: This hook will only fire when params.provider has a value, i.e. when it is an external request over REST or Sockets.

Options:

  • fieldNames (required) - One or more fields you want to remove from the object(s).

See also discard.

removeQuery

removeQuery(... fieldNames) source

Remove the given fields from the query params.

  • Used as a before hook.
  • Field names support dot notation
  • Supports multiple data items, including paginated find.
const { removeQuery } = require('feathers-hooks-common');

// Remove _id from the query for all service methods
app.service('users').before({
  all: removeQuery('_id')
});

ProTip: This hook will only fire when params.provider has a value, i.e. when it is an external request over REST or Sockets.

Options:

  • fieldNames (optional) - The fields that you want to remove from the query object.

serialize

serialize(schema: Object|Function): HookFunc source

Remove selected information from populated items. Add new computed information. Intended for use with the populate hook.

const schema = {
  only: 'updatedAt',
  computed: {
    commentsCount: (recommendation, hook) => recommendation.post.commentsInfo.length,
  },
  post: {
    exclude: ['id', 'createdAt', 'author', 'readers'],
    authorItem: {
      exclude: ['id', 'password', 'age'],
      computed: {
        isUnder18: (authorItem, hook) => authorItem.age < 18,
      },
    },
    readersInfo: {
      exclude: 'id',
    },
    commentsInfo: {
      only: ['title', 'content'],
      exclude: 'content',
    },
  },
};
purchaseOrders.after({
  all: [ populate( ... ), serialize(schema) ]
});

Options

  • schema [required, object or function] How to serialize the items.
    • Function signature (hook: Hook): Object
    • hook The hook.

The schema reflects the structure of the populated items. The base items for the example above have included post items, which themselves have included authorItem, readersInfo and commentsInfo items.

The schema for each set of items may have

  • only [optional, string or array of strings] The names of the fields to keep in each item. The names for included sets of items plus _include and _elapsed are not removed by only.
  • exclude [optional, string or array of strings] The names of fields to drop in each item. You may drop, at your own risk, names of included sets of items, _include and _elapsed.
  • computed [optional, object with functions] The new names you want added and how to compute their values.
    • Object is like { name: func, ...}
    • name The name of the field to add to the items.
    • func Function with signature (item, hook).
      • item The item with all its initial values, plus all of its included items. The function can still reference values which will be later removed by only and exclude.
      • hook The hook passed to serialize.

Serialize examples

A simple serialize

The populate example above produced the result

{ id: 9, title: 'The unbearable ligthness of FeathersJS', author: 5, yearBorn: 1990,
  authorItem: { id: 5, email: '[email protected]', name: 'John Doe' },
  _include: ['authorItem']
}

We could tailor the result more to what we need with:

const serializeSchema = {
  only: ['title'],
  authorItem: {
    only: ['name']
    computed: {
      isOver18: (authorItem, hook) => new Date().getFullYear() - authorItem.yearBorn >= 18,
    },
  }
};
app.service('posts').before({
  get: [ hooks.populate({ schema }), serialize(serializeSchema) ],
  find: [ hooks.populate({ schema }), serialize(serializeSchema) ]
});

The result would now be

{ title: 'The unbearable ligthness of FeathersJS',
  authorItem: { name: 'John Doe', isOver18: true, _computed: ['isOver18'] },
  _include: ['authorItem'],
}
Using permissions

Consider an Employee item. The Payroll Manager would be permitted to see the salaries of other department heads. No other person would be allowed to see them.

Using a function for schema allows you to select an appropriate schema based on the need.

Assume hook.params.user.roles contains an array of roles which the user performs. The Employee item can be serialized differently for the Payroll Manager than for anyone else.

const payrollSerialize = {
  'payrollMgr': { /* serialization schema for Payroll Manager */},
  'payroll': { /* serialization schema for others */}
};

employees.after({
  all: [
    populate( ... ),
    serialize(hook => payrollSerialize[
      hook.params.user.roles.contains('payrollMgr') ? 'payrollMgr' : 'payroll'
    ])    
  ]
});

setCreatedAt

setCreatedAt(fieldName = 'createdAt', ... fieldNames) source

Add the fields with the current date-time.

  • Used as a before hook for create, update or patch.
  • Used as an after hook.
  • Field names support dot notation.
  • Supports multiple data items, including paginated find.

ProTip setCreatedAt will be deprecated, so use setNow instead.

const { setCreatedAt } = require('feathers-hooks-common');

// set the `createdAt` field before a user is created
app.service('users').before({
  create: [ setCreatedAt() ]
});

Options:

  • fieldName (optional, default: createdAt) - The field that you want to add with the current date-time to the retrieved object(s).
  • fieldNames (optional) - Other fields to add with the current date-time.

See also setUpdatedAt.

setNow

setNow(... fieldNames) source

Add the fields with the current date-time.

  • Used as a before hook for create, update or patch.
  • Used as an after hook.
  • Field names support dot notation.
  • Supports multiple data items, including paginated find.
const { setNow } = require('feathers-hooks-common');

app.service('users').before({
  create: setNow('createdAt', 'updatedAt')
});

Options:

  • fieldNames (required, at least one) - The fields that you want to add with the current date-time to the retrieved object(s).

ProTip Use setNow rather than setCreatedAt or setUpdatedAt.

setSlug

setSlug(slug, fieldName = 'query.' + slug) source

A service may have a slug in its URL, e.g. storeId in app.use('/stores/:storeId/candies', new Service());. The service gets slightly different values depending on the transport used by the client.

transport hook.data.storeId hook.params.query code run on client
socketio undefined { size: 'large', storeId: '123' } candies.create({ name: 'Gummi', qty: 100 }, { query: { size: 'large', storeId: '123' } })
rest :storeId ... same as above ... same as above
raw HTTP 123 { size: 'large' } fetch('/stores/123/candies?size=large', ..

This hook normalizes the difference between the transports. A hook of all: [ hooks.setSlug('storeId') ] provides a normalized hook.params.query of { size: 'large', storeId: '123' } for the above cases.

  • Used as a before hook.
  • Field names support dot notation.
const { setSlug } = require('feathers-hooks-common');

app.service('stores').before({
  create: [ setSlug('storeId') ]
});

Options:

  • slug (required) - The slug as it appears in the route, e.g. storeId for /stores/:storeId/candies .
  • fieldName (optional, default: query[slugId]) - The field to contain the slug value.

setUpdatedAt

setUpdatedAt(fieldName = 'updatedAt', ...fieldNames) source

Add or update the fields with the current date-time.

  • Used as a before hook for create, update or patch.
  • Used as an after hook.
  • Field names support dot notation.
  • Supports multiple data items, including paginated find.

ProTip setUpdatedAt will be deprecated, so use setNow instead.

const { setUpdatedAt } = require('feathers-hooks-common');

// set the `updatedAt` field before a user is created
app.service('users').before({
  create: [ setUpdatedAt() ]
});

Options:

  • fieldName (optional, default: updatedAt) - The fields that you want to add or update in the retrieved object(s).
  • fieldNames (optional) - Other fields to add or update with the current date-time.

See also setCreatedAt.

sifter

sifter(mongoQueryFunc)) source

All official Feathers database adapters support a common way for querying, sorting, limiting and selecting find method calls. These are limited to what is commonly supported by all the databases.

The sifter hook provides an extensive MongoDB-like selection capabilities, and it may be used to more extensively select records.

  • Used as an after hook for find.
  • SProvides extensive MongoDB-like selection capabilities.

ProTip sifter filters the result of a find call. Therefore more records will be physically read than needed. You can use the Feathers database adapters query to reduce this number.

const sift = require('sift');
const { sifter } = require('feathers-hooks-common');

const selectCountry = hook => sift({ 'address.country': hook.params.country });

app.service('stores').after({
  find: sifter(selectCountry),
});
const sift = require('sift');
const { sifter } = require('feathers-hooks-common');

const selectCountry = country => () => sift({ address : { country: country } });

app.service('stores').after({
  find: sifter(selectCountry('Canada')),
});

Options:

  • mongoQueryFunc (required) - Function similar to hook => sift(mongoQueryObj). Information about the mongoQueryObj syntax is available at sift.

softDelete

softDelete(fieldName = 'deleted') source

Marks items as { deleted: true } instead of physically removing them. This is useful when you want to discontinue use of, say, a department, but you have historical information which continues to refer to the discontinued department.

  • Used as a before.all hook to handle all service methods.
  • Supports multiple data items, including paginated find.
const { softDelete } = require('feathers-hooks-common');
const dept = app.service('departments');

dept.before({
  all: softDelete(),
});

// will throw if item is marked deleted.
dept.get(0).then()

// methods can be run avoiding softDelete handling
dept.get(0, { query: { $disableSoftDelete: true }}).then()

Options:

  • fieldName (optional, default: deleted) - The name of the field holding the deleted flag.

some

some(... hookFuncs) source

Run hook functions in parallel. Return true if any hook function returned a truthy value.

  • Used as a predicate function with conditional hooks.
  • The current hook is passed to all the hook functions, and they are run in parallel.
  • Hooks to run may be sync or Promises only.
  • feathers-hooks catches any errors thrown in the predicate.
service.before({
  create: hooks.iff(hooks.some(hook1, hook2, ...), hookA, hookB, ...)
});
hooks.some(hook1, hook2, ...).call(this, currentHook)
  .then(bool => { ... });

Options:

  • hookFuncs (required) Functions which take the current hook as a param and return a boolean result.

See also every.

stashBefore

stashBefore(name) source

Stash current value of record before mutating it.

  • Used as a before hook for get, update, patch or remove.
  • An id is required in the method call.
service.before({
  patch: stashBefore()
});

Options:

  • name (optional defaults to 'before') The name of the params property to contain the current record value.

traverse

traverse(transformer, getObject) source

Traverse and transform objects in place by visiting every node on a recursive walk.

  • Used as a before or after hook.
  • Supports multiple data items, including paginated find.
  • Any object in the hook may be traversed, including the query object.
  • transformer has access to powerful methods and context.
// Trim strings
const trimmer = function (node) {
  if (typeof node === 'string') { this.update(node.trim()); }
};
service.before({ create: traverse(trimmer) });
// REST HTTP request may use the string 'null' in its query string.
// Replace these strings with the value null.
const nuller = function (node) {
  if (node === 'null') { this.update(null); }
};
service.before({ find: traverse(nuller, hook => hook.params.query) });

ProTip: GitHub's substack/js-traverse documents the extensive methods and context available to the transformer function.

Options:

  • transformer (required) - Called for every node and may change it in place.
  • getObject (optional, defaults to hook.data or hook.result) - Function with signature (hook) which returns the object to traverse.

unless

unless(predicate, ...hookFuncs) source

Resolve the predicate to a boolean. Run the hooks sequentially if the result is falsey.

  • Used as a before or after hook.
  • Predicate may be a sync or async function.
  • Hooks to run may be sync, Promises or callbacks.
  • feathers-hooks catches any errors thrown in the predicate or hook.
service.before({
  create:
    unless(isProvider('server'),
      hookA,
      unless(isProvider('rest'), hook1, hook2, hook3),
      hookB
    )
});

Options:

  • predicate (required) - Determines if hookFuncs should be run or not. If a function, predicate is called with the hook as its param. It returns either a boolean or a Promise that evaluates to a boolean.
  • hookFuncs (optional) - Zero or more hook functions. They may include other conditional hook functions.

See also iff, iffElse, else, when, isNot, isProvider.

validate

validate(validator) source

Call a validation function from a before hook. The function may be sync or return a Promise.

  • Used as a before hook for create, update or patch.

ProTip: If you have a different signature for the validator then pass a wrapper as the validator e.g. (values) => myValidator(..., values, ...).

ProTip: Wrap your validator in callbackToPromise if it uses a callback.

const { callbackToPromise, validate } = require('feathers-hooks-common');

// function myCallbackValidator(values, cb) { ... }
const myValidator = callbackToPromise(myCallbackValidator, 1); // function requires 1 param
app.service('users').before({ create: validate(myValidator) });

Options:

  • validator (required) - Validation function with signature function validator(formValues, hook).

Sync functions return either an error object like { fieldName1: 'message', ... } or null. Validate will throw on an error object with throw new errors.BadRequest({ errors: errorObject });.

Promise functions should throw on an error or reject with new errors.BadRequest('Error message', { errors: { fieldName1: 'message', ... } }); Their .then returns either sanitized values to replace hook.data, or null.

Example

Comprehensive validation may include the following:

  • Object schema validation. Checking the item object contains the expected properties with values in the expected format. The values might get sanitized. Knowing the item is well formed makes further validation simpler.
  • Re-running any validation supposedly already done on the front-end. It would an asset if the server can re-run the same code the front-end used.
  • Performing any validation and sanitization unique to the server.

A full featured example of such a process appears below. It validates and sanitizes a new user before adding the user to the database.

  • The form expects to be notified of errors in the format { email: 'Invalid email.', password: 'Password must be at least 8 characters.' }.
  • The form calls the server for async checking of selected fields when control leaves those fields. This for example could check that an email address is not already used by another user.
  • The form does local sync validation when the form is submitted.
  • The code performing the validations on the front-end is also used by the server.
  • The server performs schema validation using Walmart's Joi.
  • The server does further validation and sanitization.

Validation using Validate

// file /server/services/users/hooks/index.js
const auth = require('feathers-authentication').hooks;
const { callbackToPromise, remove, validate } = require('feathers-hooks-common');
const validateSchema = require('feathers-hooks-validate-joi');

const clientValidations = require('/common/usersClientValidations');
const serverValidations = require('/server/validations/usersServerValidations');
const schemas = require('/server/validations/schemas');

const serverValidationsSignup = callbackToPromise(serverValidations.signup, 1);

exports.before = {
  create: [
    validateSchema.form(schemas.signup, schemas.options), // schema validation
    validate(clientValidations.signup), // re-run form sync validation
    validate(values => clientValidations.signupAsync(values, 'someMoreParams')), // re-run form async
    validate(serverValidationsSignup), // run server validation
    remove('confirmPassword'),
    auth.hashPassword()
  ]
};

Validation routines for front and back-end.

Validations used on front-end. They are re-run by the server.

// file /common/usersClientValidations
// Validations for front-end. Also re-run on server.
const clientValidations = {};

// sync validation of signup form on form submit
clientValidations.signup = values => {
  const errors = {};

  checkName(values.name, errors);
  checkUsername(values.username, errors);
  checkEmail(values.email, errors);
  checkPassword(values.password, errors);
  checkConfirmPassword(values.password, values.confirmPassword, errors);

  return errors;
};

// async validation on exit from some fields on form
clientValidations.signupAsync = values =>
  new Promise((resolve, reject) => {
    const errs = {};

    // set a dummy error
    errs.email = 'Already taken.';

    if (!Object.keys(errs).length) {
      resolve(null); // 'null' as we did not sanitize 'values'
    }
    reject(new errors.BadRequest('Values already taken.', { errors: errs }));
  });

module.exports = clientValidations;

function checkName(name, errors, fieldName = 'name') {
  if (!/^[\\sa-zA-Z]{8,30}$/.test((name || '').trim())) {
    errors[fieldName] = 'Name must be 8 or more letters or spaces.';
  }
}

Schema definitions used by the server.

// file /server/validations/schemas
const Joi = require('joi');

const username = Joi.string().trim().alphanum().min(5).max(30).required();
const password = Joi.string().trim().regex(/^[\sa-zA-Z0-9]+$/, 'letters, numbers, spaces')
  .min(8).max(30).required();
const email = Joi.string().trim().email().required();

module.exports = {
  options: { abortEarly: false, convert: true, allowUnknown: false, stripUnknown: true },
  signup: Joi.object().keys({
    name: Joi.string().trim().min(8).max(30).required(),
    username,
    password,
    confirmPassword: password.label('Confirm password'),
    email
  })
};

Validations run by the server.

// file /server/validations/usersServerValidations
// Validations on server. A callback function is used to show how the hook handles it.
module.exports = {
  signup: (data, cb) => {
    const formErrors = {};
    const sanitized = {};

    Object.keys(data).forEach(key => {
      sanitized[key] = (data[key] || '').trim();
    });

    cb(Object.keys(formErrors).length > 0 ? formErrors : null, sanitized);
  }
};

See also validateSchema.

validateSchema

validateSchema(schema, ajv, options) source

Validate an object using JSON-Schema through AJV

ProTip There are some good tutorials on using JSON-Schema with ajv.

  • Used as a before or after hook.
  • The hook will throw if the data does not match the JSON-Schema. error.errors will, by default, contain an array of error messages.

ProTip You may customize the error message format with a custom formatting function. You could, for example, return { name1: message, name2: message } which could be more suitable for a UI.

ProTip If you need to customize ajv with new keywords, formats or schemas, then instead of passing the Ajv constructor, you may pass in an instance of Ajv as the second parameter. In this case you need to pass ajv options to the ajv instance when newing, rather than passing them in the third parameter of validateSchema. See the second example below.

const Ajv = require('ajv');
const createSchema = { /* JSON-Schema */ };
module.before({
  create: validateSchema(createSchema, Ajv)
});
const Ajv = require('ajv');
const ajv = new Ajv({ allErrors: true, $data: true });
ajv.addFormat('allNumbers', '^\d+$');
const createSchema = { /* JSON-Schema */ };
module.before({
  create: validateSchema(createSchema, ajv)
});

Options:

  • schema (required) - The JSON-Schema.
  • ajv (required) - The ajv validator. Could be either the Ajv constructor or an instance of it.
  • options (optional) - Options.
    • Any ajv options. Only effective when the second parameter is the Ajv constructor.
    • addNewError (optional) - Custom message formatter. Its a reducing function which works similarly to Array.reduce(). Its signature is { currentFormattedMessages: any, ajvError: AjvError, itemsLen: number, index: number }: newFormattedMessages
      • currentFormattedMessages - Formatted messages so far. Initially null.
      • ajvError - ajv error.
      • itemsLen - How many data items there are. 1-based.
      • index - Which item this is. 0-based.
      • newFormattedMessages - The function returns the updated formatted messages.

when

An alias for iff source

Util: callbackToPromise

callbackToPromise(callbackFunc, paramsCount) source

Wrap a function calling a callback into one that returns a Promise.

  • Promise is rejected if the function throws.
const { callbackToPromise } = require('feathers-hooks-common');

function tester(data, a, b, cb) {
  if (data === 3) { throw new Error('error thrown'); }
  cb(data === 1 ? null : 'bad', data);
} 
const wrappedTester = callbackToPromise(tester, 3); // because func call requires 3 params

wrappedTester(1, 2, 3); // tester(1, 2, 3, wrapperCb)
wrappedTester(1, 2); // tester(1, 2, undefined, wrapperCb)
wrappedTester(); // tester(undefined, undefined undefined, wrapperCb)
wrappedTester(1, 2, 3, 4, 5); // tester(1, 2, 3, wrapperCb)

wrappedTester(1, 2, 3).then( ... )
  .catch(err => { console.log(err instanceof Error ? err.message : err); });

Options:

  • callbackFunc (required) - A function which uses a callback as its last param.
  • paramsCount (required) - The number of parameters callbackFunc expects. This count does not include the callback param itself.

The wrapped function will always be called with that many params, preventing potential bugs.

See also promiseToCallback.

Util: checkContext

checkContext(hook, type, methods, label) source

Restrict the hook to a hook type (before, after) and a set of hook methods (find, get, create, update, patch, remove).

const { checkContext } = require('feathers-hooks-common');

function myHook(hook) {
  checkContext(hook, 'before', ['create', 'remove']);
  ...
}

app.service('users').after({
  create: [ myHook ] // throws
});

// checkContext(hook, 'before', ['update', 'patch'], 'hookName');
// checkContext(hook, null, ['update', 'patch']);
// checkContext(hook, 'before', null, 'hookName');
// checkContext(hook, 'before');

Options:

  • hook (required) - The hook provided to the hook function.
  • type (optional) - The hook may be run in before or after. null allows the hook to be run in either.
  • methods (optional) - The hook may be run for these methods.
  • label (optional) - The label to identify the hook in error messages, e.g. its name.

Util: deleteByDot

deleteByDot(obj, path) source

deleteByDot deletes a property from an object using dot notation, e.g. employee.address.city.

import { deleteByDot } from 'feathers-hooks-common';

const discardPasscode = () => (hook) => {
  deleteByDot(hook.data, 'security.passcode');
}

app.service('directories').before = {
  find: discardPasscode()
};

Options:

  • obj (required) - The object containing the property we want to delete.
  • path (required) - The path to the data, e.g. security.passcode. Array notion is not supported, e.g. order.lineItems[1].quantity.

See also existsByDot, getByDot, setByDot.

Util: existsByDot

existsByDot(obj, path) source

existsByDot checks if a property exists in an object using dot notation, e.g. employee.address.city. Properties with a value of undefined are considered to exist.

import { discard, existsByDot, iff } from 'feathers-hooks-common';

const discardBadge = () => iff(!existsByDot('security.passcode'), discard('security.badge'));

app.service('directories').before = {
  find: discardBadge()
};

Options:

  • obj (required) - The object containing the property.
  • path (required) - The path to the property, e.g. security.passcode. Array notion is not supported, e.g. order.lineItems[1].quantity.

See also existsByDot, getByDot, setByDot.

Util: getByDot, setByDot

getByDot(obj, path) source

setByDot(obj, path, value, ifDelete) source

getByDot gets a value from an object using dot notation, e.g. employee.address.city. It does not differentiate between non-existent paths and a value of undefined.

setByDot is the companion to getByDot. It sets a value in an object using dot notation.

import { getByDot, setByDot } from 'feathers-hooks-common';

const setHomeCity = () => (hook) => {
  const city = getByDot(hook.data, 'person.address.city');
  setByDot(hook, 'data.person.home.city', city);
}

app.service('directories').before = {
  create: setHomeCity()
};

Options:

  • obj (required) - The object we get data from or set data in.
  • path (required) - The path to the data, e.g. person.address.city. Array notion is not supported, e.g. order.lineItems[1].quantity.
  • value (required) - The value to set the data to.

See also existsByDot, deleteByDot.

Util: getItems, replaceItems

getItems(hook) source

replaceItems(hook, items) source

getItems gets the data items in a hook. The items may be hook.data, hook.result or hook.result.data depending on where the hook is used, the method its used with and if pagination is used. undefined, an object or an array of objects may be returned.

replaceItems is the companion to getItems. It updates the data items in the hook.

  • Handles before and after hooks.
  • Handles paginated and non-paginated results from find.
import { getItems, replaceItems } from 'feathers-hooks-common';

const insertCode = (code) => (hook) {
    const items = getItems(hook);
    !Array.isArray(items) ? items.code = code : (items.forEach(item => { item.code = code; }));
    replaceItems(hook, items);
  }

app.service('messages').before = { 
  create: insertCode('a')
};

The common hooks usually mutate the items in place, so a replaceItems is not required.

const items = getItems(hook);
(Array.isArray(items) ? items : [items]).forEach(item => { item.setCreateAt = new Date(); });

Options:

  • hook (required) - The hook provided to the hook function.
  • items (required) - The updated item or array of items.

Util: paramsForServer

paramsForServer(params, ... whitelist) source

A client utility to pass selected params properties to the server.

  • Companion to the server-side hook paramsFromClient.

By default, only the hook.params.query object is transferred to the server from a Feathers client, for security among other reasons. However you can explicitly transfer other params props with the client utility function paramsForServer in conjunction with the hook function paramsFromClient on the server.

// client
import { paramsForServer } from 'feathers-hooks-common';
service.patch(null, data, paramsForServer({
  query: { dept: 'a' }, populate: 'po-1', serialize: 'po-mgr'
}));

// server
const { paramsFromClient } = require('feathers-hooks-common');
service.before({ all: [
  paramsFromClient('populate', 'serialize', 'otherProp'),
  myHook
]});

// myHook's `hook.params` will now be
// { query: { dept: 'a' }, populate: 'po-1', serialize: 'po-mgr' } }

Options:

  • params (optional) The params object to pass to the server, including any query prop.
  • whitelist (optional) Names of the props in params to transfer to the server. This is a security feature. All props are transferred if no whitelist is specified.

See paramsFromClient.

Util: promiseToCallback

promiseToCallback(promise)(callbackFunc) source

Wrap a Promise into a function that calls a callback.

  • The callback does not run in the Promise's scope. The Promise's catch chain is not invoked if the callback throws.
import { promiseToCallback } from 'feathers-hooks-common'

function (cb) {
  const promise = new Promise( ...).then( ... ).catch( ... );
  ...
  promiseToCallback(promise)(cb);
  promise.then( ... ); // this is still possible
}

Options:

  • promise (required) - A function returning a promise.

See also callbackToPromise.

FAQ: Coerce data types

A common need is converting fields coming in from query params. These fields are provided as string values by default and you may need them as numbers, boolenas, etc.

The validateSchema does a wide selection of type coercions, as well as checking for missing and unexpected fields.