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AutoRest Extensions for Swagger 2.0

Introduction

The following documents describes AutoRest specific vendor extensions for Swagger 2.0 schema. Some of the extensions are only applicable to Microsoft Azure and as such are only available in Azure code generators (e.g. Azure.CSharp, Azure.NodeJS, etc.).

Generic Extensions

Microsoft Azure Extensions

##x-ms-code-generation-settings x-ms-code-generation-settings extension on info element enables passing code generation settings via swagger document.

Parent element: Info Object

Schema:

Field Name Type Description
.* string or bool Required. Field name should be a valid autorest.exe parameter. Value should be a valid string value or boolean for flag parameters

Example:

"info": {
   "x-ms-code-generation-settings": {
      "header": "MIT",
      "internalConstructors": true
   }
}

x-ms-skip-url-encoding

By default, path parameters will be URL-encoded automatically. This is a good default choice for user-provided values. This is not a good choice when the parameter is provided from a source where the value is known to be URL-encoded. The URL encoding is NOT an idempotent operation. For example, the percent character "%" is URL-encoded as "%25". If the parameter is URL-encoded again, "%25" becomes "%2525". Mark parameters where the source is KNOWN to be URL-encoded to prevent the automatic encoding behavior.

Parent element: Parameter Object

Schema: true|false

Example:

"parameters": [
  {
    "name": "databaseName",
    "in": "path",
    "type": "string",
    "required": true,
    "x-ms-skip-url-encoding": true
  }
]

x-ms-enum

Enum definitions in Swagger indicate that only a particular set of values may be used for a property or parameter. When the property is represented on the wire as a string, it would be a natural choice to represent the property type in C# and Java as an enum. However, not all enumeration values should necessarily be represented as strongly typed enums - there are additional considerations, such as how often expected values might change, since adding a new value to a strongly typed enum is a breaking change requiring an updated API version. Additionally, there is some metadata that is required to create a useful enum, such as a descriptive name, which is not represented in swagger. For this reason, enums are not automatically turned into strongly typed enum types - instead they are rendered in the documentation comments for the property or parameter to indicate allowed values. To indicate that an enum will rarely change and that C#/Java enum semantics are desired, use the x-ms-enum exension. Note that depending on the code generation language the behavior of this extension may differ.

In C# and Java, an enum type is generated and is declared as the type of the related request/response object. The enum is serialized as the string expected by the REST API.

Parent element: Parameter Object, Schema Object, Items Object, or Header Object

Schema:

Field Name Type Description
name string Required. Specifies the name for the Enum.
modelAsString boolean Default: false When set to true the enum will be modeled as a string. No validation will happen. When set to false, it will be modeled as an enum if that language supports enums. Validation will happen, irrespective of support of enums in that language.

Example:

  "accountType": {
    "type": "string",
    "enum": [
      "Standard_LRS",
      "Standard_ZRS",
      "Standard_GRS",
      "Standard_RAGRS",
      "Premium_LRS"
    ],
    "x-ms-enum": {
      "name": "AccountType",
      "modelAsString": false
    }
  }

Single value enum as a constant

  • If the single value enum is a required model property or a required parameter then it is always treated as a constant. The x-ms-enum extension is ignored.
    • Explanation: The above condition specifies that the server always expects the model property or the parameter and with a specific value. Hence, it makes sense to treat it as a constant. In the future, if more values are added to the enum then, it is a breaking change to the API provided by the client library.
  • If the single value enum is an optional model property or an optional parameter and if x-ms-enum extension is provided then it will be honoured.

##x-ms-parameter-grouping By default operation parameters are generated in the client as method arguments. This behavior can sometimes be undesirable when the number of parameters is high. x-ms-parameter-grouping extension is used to group multiple primitive parameters into a composite type to improve the API.

Parent element: Parameter Object

Schema:

Field Name Type Description
name string When set, specifies the name for the composite type.
postfix string Alternative to name parameter. If specified the name of the composite type will be generated as follows {MethodGroup}{Method}{Postfix}.

If none of the parameters are set the name of the composite type is generated as follows {MethodGroup}{Method}Parameters.

Example:

"/some/{pathParam1}/{pathParam2}": {
  "operationId": "Update",
  "post": {
    "parameters": [
    {
        "name": "headerParam",
        "in": "header",
        "type": "string",
        "required": false,
        "x-ms-parameter-grouping": {
          "name": "custom-parameter-group"
        }
    },
    {
        "name": "pathParam1",
        "in": "path",
        "type": "string",
        "required": true,
        "x-ms-parameter-grouping": {
          "name": "custom-parameter-group"
        }
    },
    {
        "name": "pathParam2",
        "in": "path",
        "type": "string",
        "required": true,
        "x-ms-parameter-grouping": {
          "name": "custom-parameter-group"
        }
    }]
  }
}

Above Swagger schema will produce a type CustomParameterGroup with 3 properties (if applicable in the generator language).

x-ms-paths

Swagger 2.0 has a built-in limitation on paths. Only one operation can be mapped to a path and http method. There are some APIs, however, where multiple distinct operations are mapped to the same path and same http method. For example GET /mypath/query-drive?op=file and GET /mypath/query-drive?op=folder may return two different model types (stream in the first example and JSON model representing Folder in the second). Since Swagger does not treat query parameters as part of the path the above 2 operations may not co-exist in the standard "paths" element.

To overcome this limitation an "x-ms-paths" extension was introduced parallel to "paths". Urls under "x-ms-paths" are allowed to have query parameters for disambiguation, however they are removed during model parsing.

Parent element: Swagger Object

Schema: The x-ms-paths extension has the same schema as Paths Object with exception that Path Item Object can have query parameters.

Example:

"paths":{
   "/pets": {
        "get": {
            "parameters": [
                {
                     "name": "name",
                     "required": true
                }
            ]
        }
   }
},
"x-ms-paths":{   
   "/pets?color={color}": {
        "get": {}
   },
}

##x-ms-client-name

In some situations, data passed by name, such as query parameters, entity headers, or elements of a JSON document body, are not suitable for use in client-side code. For example, a header like 'x-ms-version' would turn out like xMsVersion, or x_ms_version, or XMsVersion, depending on the preferences of a particular code generator. It may be better to allow a code generator to use 'version' as the name of the parameter in client code.

By using the 'x-ms-client-name' extension, a name can be defined for use specifically in code generation, separately from the name on the wire. It can be used for query parameters and header parameters, as well as properties of schemas.

Parameter Example:

  "parameters": {
    "ApiVersionParameter": {
      "name": "x-ms-version",
      "x-ms-client-name": "version",
      "in": "header",
      "required": false,
      "type": "string",
      "x-ms-global": true,
      "enum": [
        "2015-04-05",
        "2014-02-14",
        "2013-08-15",
        "2012-02-12",
        "2011-08-18",
        "2009-09-19",
        "2009-07-17",
        "2009-04-14"
      ],
      "default": "2015-04-05",
      "description": "Specifies the version of the operation to use for this request."
    }

Property Example:

{
  "definitions": {
    "Product": {
      "x-ms-external" : true,
      "properties": {
        "product_id": {
          "type": "string"
		  "x-ms-client-name": "SKU"          
        }
     }
  }
}

##x-ms-external To allow generated clients to share models via shared libraries an x-ms-external extension was introduced. When a Definition Objects contains this extensions it's definition will be excluded from generated library. Note that in strongly typed languages the code will not compile unless the assembly containing the type is referenced with the project/library.

Parent element: Definition Objects

Schema: true|false

Example:

{
  "definitions": {
    "Product": {
      "x-ms-external" : true,
      "properties": {
        "product_id": {
          "type": "string"          
        }
     }
  }
}

##x-ms-discriminator-value Swagger 2.0 specification requires that when used, the value of discriminator field MUST match the name of the schema or any schema that inherits it. To overcome this limitation x-ms-discriminator-value extension was introduced.

Schema: string - the expected value of the discriminator field on the wire.

Parent element: Schema Object

Example:

"definitions": {
  "SqlDefinition": {
      "x-ms-discriminator-value": "USql",
      "allOf": [
        {
          "$ref": "#/definitions/SqlProperties"
        }
      ]
   }
}

##x-ms-client-flatten This extension allows to flatten deeply nested payloads into a more user friendly object. For example a payload that looks like this on the wire:

{
  "template": {
    "name": "some name",
    "properties": {
      "prop1": "value1",
      "prop2": "value2",
      "url": {
        "value": "http://myurl"
      }    
    } 
  }
}

can be transformed into the following client model:

public class Template 
{
    public string Name {get;set;}
    public string Prop1 {get;set;}
    public string Prop2 {get;set;}
    public string UrlValue {get;set;}
}

by using the following swagger definition:

"definitions": {
  "template": {
    "properties": {
	    "name": {
	      "type": "string"
        },
	    "properties": {
	      "x-ms-client-flatten": true,
	      "$ref": "#/definitions/templateProperties"
	    } 
    }
  }
}

It's also possible to flatten body parameters so that the method will look like this:

client.DeployTemplate("some name", "value1", "value2", "http://myurl");

by using the following swagger definition:

"post": {
  "operationId": "DeployTemplate",        
  "parameters": [
  {
     "name": "body",
     "in": "body",
     "x-ms-client-flatten": true,
     "schema": {
       "$ref": "#/definitions/template"
     }
    }
  ]
}

Parent element: Parameter Objects or Property on the Schema Definition. In both cases the type of the parameter or property should be a complex schema with properties.

Schema: true|false

Example:

"definitions": {
  "template": {
    "properties": {
	    "name": {
	      "type": "string"
        },
	    "properties": {
	      "x-ms-client-flatten": true,
	      "$ref": "#/definitions/templateProperties"
	    } 
    }
  }
}

and

"post": {
  "operationId": "DeployTemplate",        
  "parameters": [
  {
     "name": "body",
     "in": "body",
     "x-ms-client-flatten": true,
     "schema": {
       "$ref": "#/definitions/template"
     }
    }
  ]
}

##x-ms-parameterized-host When used, replaces the standard Swagger "host" attribute with a host that contains variables to be replaced as part of method execution or client construction, very similar to how path parameters work.

Parent element: Info Object

Schema:

Field Name Type Description
hostTemplate string Required. Specifies the parameterized template for the host.
useSchemePrefix boolean Optional, Default: true. Specifes whether to prepend the default scheme a.k.a protocol to the base uri of client.
positionInOperation string Optional, Default: first. Specifies whether the list of parameters will appear in the beginning or in the end, in the method signature for every operation. The order within the parameters provided in the below mentioned array will be preserved. Either the array of parameters will be prepended or appended, based on the value provided over here. Valid values are "first", "last". Every method/operation in any programming language has parameters categorized into two buckets "required" and "optional". It is natural for optional paramaters to appear in the end in a method signature. This aspect will be preserved, while prepending(first) or appending(last) hostTemplate parameters .
parameters Array of Parameter Objects The list of parameters that are used within the hostTemplate. This can include both reference parameters as well as explicit parameters. Note that "in" is required and must be set to "path". The reference parameters will be treated as global parameters and will end up as property of the client.

Example:

  • Using both explicit and reference parameters.
    • Since "useSchemePrefix" is not specified, it's default value true will be applied. The user is expected to provide only the value of accountName. The generated code will fit it as a part of the url.
    • Since "positionInOperation" with value "last" is specified, "accountName" will be the last required parameter in every method. "adlaJobDnsSuffixInPath" will be a property on the client as it is defined in the global parameters section and is referenced here.
"x-ms-parameterized-host": {
    "hostTemplate": "{accountName}.{adlaJobDnsSuffix}",
    "positionInOperation": "last",
    "parameters": [
      {
        "name": "accountName",
        "description": "The Azure Data Lake Analytics account to execute job operations on.",
        "required": true,
        "type": "string",
        "in": "path",
        "x-ms-skip-url-encoding": true
      },
      {
        "$ref": "#/parameters/adlaJobDnsSuffixInPath"
      }
    ]
  }
...
"adlaJobDnsSuffixInPath": {
      "name": "adlaJobDnsSuffix",
      "in": "path",
      "required": true,
      "type": "string",
      "default": "azuredatalakeanalytics.net",
      "x-ms-skip-url-encoding": true,
      "description": "Gets the DNS suffix used as the base for all Azure Data Lake Analytics Job service requests."
    }
  • Using explicit parameters and specifying the positionInOperation and schemePrefix.
    • This means that accountName will be the first required parameter in all the methods and the user is expected to provide a url (protocol + accountName), since "useSchemePrfix" is set to false.
"x-ms-parameterized-host": {
    "hostTemplate": "{accountName}.mystaticsuffix.com",
    "useSchemePrefix": false,
    "positionInOperation": "first",
    "parameters": [
      {
        "name": "accountName",
        "description": "The Azure Data Lake Analytics account to execute job operations on.",
        "required": true,
        "type": "string",
        "in": "path",
        "x-ms-skip-url-encoding": true
      }
    ]
  }

##x-ms-odata When present the x-ms-odata extensions indicates the operation includes one or more OData query parameters. These parameters inlude $filter, $top, $orderby, $skip, and $expand. In some languages the generated method will expose these parameters as strongly types OData type.

Schema: ref to the definition that describes object used in filter.

Parent element: Operation Object

Example:

"paths": {    
  "/subscriptions/resource": {
    "get": {
      "x-ms-odata": "#/definitions/Product"
    }
  }
}

##x-ms-pageable The REST API guidelines define a common pattern for paging through lists of data. The operation response is modeled in Swagger as the list of items and the nextLink. Tag the operation as x-ms-pageable and the generated code will include methods for navigating between pages.

Schema:

Field Name Type Description
nextLinkName string Specifies the name of the property that provides the nextLink. If the model does not have the nextLink property then specify null. This will be useful for the services that return an object that has an array referenced by the itemName. The object is flattened in a way that the array is directly returned. Since the nextLinkName is explicitly specified to null, the generated code will not implement paging. However, you get the benefit of flattening. Thus providing a better client side API to the end user.
itemName string Specifies the name of the property that provides the collection of pageable items. Default value is 'value'.{Postfix}`.
operationName string Specifies the name of the Next operation. Default value is 'XXXNext' where XXX is the name of the operation

Parent element: Operation Object

Example: x-ms-pageable operation definition

"paths": {
  "/products": {
    "get": {
      "x-ms-pageable": {
        "nextLinkName": "nextLink"
      },
      "operationId": "products_list",
      "description": "A pageable list of Products.",
      "responses": {
        "200": {
          "schema": {
            "$ref": "#/definitions/ProductListResult"
          }
        }
      }
    }
  }
}

x-ms-pageable model definition

"ProductListResult": {
  "properties": {
    "value": {
      "type": "array",
      "items": {
        "$ref": "#/definitions/Product"
      }
    },
    "nextLink": {
      "type": "string"
    }
  }
}

##x-ms-long-running-operation Some requests like creating/deleting a resource cannot be carried out immediately. In such a situation, the server sends a 201 (Created) or 202 (Accepted) and provides a link to monitor the status of the request. When such an operation is marked with extension "x-ms-long-running-operation": true, in Swagger, the generated code will know how to fetch the link to monitor the status. It will keep on polling at regular intervals till the request reaches one of the terminal states: Succeeded, Failed, or Canceled.

Parent element: Operation Object

Schema: true|false

Example:

"paths": {
  "/products/{name}": {
    "put": {
      "operationId": "products_create",
      "x-ms-long-running-operation": true,
      "description": "A pageable list of Products."
    }
  }
}

##x-ms-azure-resource Resource types as defined by the Resource Managemer API are tagged by using a x-ms-azure-resource extension.

Parent element: Schema Object

Schema: true|false

Example:

"Resource": {
  "x-ms-azure-resource": true,
  "properties": {
    "id": {
      "type": "string",
      "readOnly": true,
      "description": "Resource Id"
    }
  }
}

##x-ms-request-id When set, allows to overwrite the x-ms-request-id response header (default is x-ms-request-id).

Parent element: Operation Object

Schema: string - the name of the request id header to use when setting Response.RequestId property.

Example:

"paths": {
  "/products/{name}": {
    "get": {
      "operationId": "products_create",
      "x-ms-request-id": "request-id"
    }
  }
}

##x-ms-client-request-id When set, specifies the header parameter to be used instead of x-ms-client-request-id (default is x-ms-client-request-id).

Parent element: Header Parameter Object

Schema: string - the name of the client request id header to use when setting sending request.

Example:

"paths": {
  "/products/{name}": {
    "get": {
      "operationId": "products_create",
      "parameters": [{
        "name": "x-ms-client-request-id",
        "in": "header",
        "type": "string",
        "required": false,
        "x-ms-client-request-id": true
      }]
    }
  }
}