Core Data: Implement _fields data reuse for entities

docs/designers-developers/developers/data/data-core.md

@@ -152,18 +152,21 @@ _Returns_
 
 <a name="getEntityRecord" href="#getEntityRecord">#</a> **getEntityRecord**
 
-Returns the Entity's record object by key.
+Returns the Entity's record object by key. Returns `null` if the value is not
+yet received, undefined if the value entity is known to not exist, or the
+entity object if it exists and is received.
 
 _Parameters_
 
 -   _state_ `Object`: State tree
 -   _kind_ `string`: Entity kind.
 -   _name_ `string`: Entity name.
 -   _key_ `number`: Record's key
+-   _query_ `?Object`: Optional query.
 
 _Returns_
 
--   `?Object`: Record.
+-   `(?Object|null)`: Record.
 
 <a name="getEntityRecordEdits" href="#getEntityRecordEdits">#</a> **getEntityRecordEdits**
 
@@ -348,6 +351,22 @@ _Returns_
 
 -   `boolean`: Whether the entity record has edits or not.
 
+<a name="hasEntityRecords" href="#hasEntityRecords">#</a> **hasEntityRecords**
+
+Returns true if records have been received for the given set of parameters,
+or false otherwise.
+
+_Parameters_
+
+-   _state_ `Object`: State tree
+-   _kind_ `string`: Entity kind.
+-   _name_ `string`: Entity name.
+-   _query_ `?Object`: Optional terms query.
+
+_Returns_
+
+-   `boolean`: Whether entity records have been received.
+
 <a name="hasFetchedAutosaves" href="#hasFetchedAutosaves">#</a> **hasFetchedAutosaves**
 
 Returns true if the REST request for autosaves has completed.

packages/core-data/README.md

@@ -389,18 +389,21 @@ _Returns_
 
 <a name="getEntityRecord" href="#getEntityRecord">#</a> **getEntityRecord**
 
-Returns the Entity's record object by key.
+Returns the Entity's record object by key. Returns `null` if the value is not
+yet received, undefined if the value entity is known to not exist, or the
+entity object if it exists and is received.
 
 _Parameters_
 
 -   _state_ `Object`: State tree
 -   _kind_ `string`: Entity kind.
 -   _name_ `string`: Entity name.
 -   _key_ `number`: Record's key
+-   _query_ `?Object`: Optional query.
 
 _Returns_
 
--   `?Object`: Record.
+-   `(?Object|null)`: Record.
 
 <a name="getEntityRecordEdits" href="#getEntityRecordEdits">#</a> **getEntityRecordEdits**
 
@@ -585,6 +588,22 @@ _Returns_
 
 -   `boolean`: Whether the entity record has edits or not.
 
+<a name="hasEntityRecords" href="#hasEntityRecords">#</a> **hasEntityRecords**
+
+Returns true if records have been received for the given set of parameters,
+or false otherwise.
+
+_Parameters_
+
+-   _state_ `Object`: State tree
+-   _kind_ `string`: Entity kind.
+-   _name_ `string`: Entity name.
+-   _query_ `?Object`: Optional terms query.
+
+_Returns_
+
+-   `boolean`: Whether entity records have been received.
+
 <a name="hasFetchedAutosaves" href="#hasFetchedAutosaves">#</a> **hasFetchedAutosaves**
 
 Returns true if the REST request for autosaves has completed.

packages/core-data/src/queried-data/get-query-parts.js

@@ -6,17 +6,20 @@ import { addQueryArgs } from '@wordpress/url';
 /**
  * Internal dependencies
  */
-import { withWeakMapCache } from '../utils';
+import { withWeakMapCache, getNormalizedCommaSeparable } from '../utils';
 
 /**
  * An object of properties describing a specific query.
  *
  * @typedef {Object} WPQueriedDataQueryParts
  *
- * @property {number} page      The query page (1-based index, default 1).
- * @property {number} perPage   Items per page for query (default 10).
- * @property {string} stableKey An encoded stable string of all non-pagination
- *                              query parameters.
+ * @property {number}      page      The query page (1-based index, default 1).
+ * @property {number}      perPage   Items per page for query (default 10).
+ * @property {string}      stableKey An encoded stable string of all non-
+ *                                   pagination, non-fields query parameters.
+ * @property {?(string[])} fields    Target subset of fields to derive from
+ *                                   item objects.
+ * @property {?(number[])} include   Specific item IDs to include.
  */
 
 /**
@@ -36,6 +39,8 @@ export function getQueryParts( query ) {
 		stableKey: '',
 		page: 1,
 		perPage: 10,
+		fields: null,
+		include: null,
 	};
 
 	// Ensure stable key by sorting keys. Also more efficient for iterating.
@@ -49,10 +54,21 @@ export function getQueryParts( query ) {
 			case 'page':
 				parts[ key ] = Number( value );
 				break;
+
 			case 'per_page':
 				parts.perPage = Number( value );
 				break;
 
+			case 'include':
+				parts.include = getNormalizedCommaSeparable( value ).map(
+					Number
+				);
+				break;
+
+			case '_fields':
+				parts.fields = getNormalizedCommaSeparable( value );
+				break;
+
 			default:
 				// While it could be any deterministic string, for simplicity's
 				// sake mimic querystring encoding for stable key.

packages/core-data/src/queried-data/reducer.js

@@ -93,6 +93,47 @@ function items( state = {}, action ) {
 	return state;
 }
 
+/**
+ * Reducer tracking item completeness, keyed by ID. A complete item is one for
+ * which all fields are known. This is used in supporting `_fields` queries,
+ * where not all properties associated with an entity are necessarily returned.
+ * In such cases, completeness is used as an indication of whether it would be
+ * safe to use queried data for a non-`_fields`-limited request.
+ *
+ * @param {Object<string,boolean>} state  Current state.
+ * @param {Object} action Dispatched action.
+ *
+ * @return {Object<string,boolean>} Next state.
+ */
+export function itemIsComplete( state = {}, action ) {
+	const { type, query, key = DEFAULT_ENTITY_KEY } = action;
+	if ( type !== 'RECEIVE_ITEMS' ) {
+		return state;
+	}
+
+	// An item is considered complete if it is received without an associated
+	// fields query. Ideally, this would be implemented in such a way where the
+	// complete aggregate of all fields would satisfy completeness. Since the
+	// fields are not consistent across all entity types, this would require
+	// introspection on the REST schema for each entity to know which fields
+	// compose a complete item for that entity.
+	const isCompleteQuery =
+		! query || ! Array.isArray( getQueryParts( query ).fields );
+
+	return {
+		...state,
+		...action.items.reduce( ( result, item ) => {
+			const itemId = item[ key ];
+
+			// Defer to completeness if already assigned. Technically the
+			// data may be outdated if receiving items for a field subset.
+			result[ itemId ] = state[ itemId ] || isCompleteQuery;
+
+			return result;
+		}, {} ),
+	};
+}
+
 /**
  * Reducer tracking queries state, keyed by stable query key. Each reducer
  * query object includes `itemIds` and `requestingPageByPerPage`.
@@ -171,5 +212,6 @@ const queries = ( state = {}, action ) => {
 
 export default combineReducers( {
 	items,
+	itemIsComplete,
 	queries,
 } );

packages/core-data/src/queried-data/selectors.js

@@ -27,13 +27,23 @@ const queriedItemsCacheByState = new WeakMap();
  * @return {?Array} Query items.
  */
 function getQueriedItemsUncached( state, query ) {
-	const { stableKey, page, perPage } = getQueryParts( query );
+	const { stableKey, page, perPage, include, fields } = getQueryParts(
+		query
+	);
 
-	if ( ! state.queries[ stableKey ] ) {
-		return null;
+	let itemIds;
+	if ( Array.isArray( include ) && ! stableKey ) {
+		// If the parsed query yields a set of IDs, but otherwise no filtering,
+		// it's safe to consider targeted item IDs as the include set. This
+		// doesn't guarantee that those objects have been queried, which is
+		// accounted for below in the loop `null` return.
+		itemIds = include;
+		// TODO: Avoid storing the empty stable string in reducer, since it
+		// can be computed dynamically here always.
+	} else if ( state.queries[ stableKey ] ) {
+		itemIds = state.queries[ stableKey ];
 	}
 
-	const itemIds = state.queries[ stableKey ];
 	if ( ! itemIds ) {
 		return null;
 	}
@@ -47,7 +57,43 @@ function getQueriedItemsUncached( state, query ) {
 	const items = [];
 	for ( let i = startOffset; i < endOffset; i++ ) {
 		const itemId = itemIds[ i ];
-		items.push( state.items[ itemId ] );
+		if ( Array.isArray( include ) && ! include.includes( itemId ) ) {
+			continue;
+		}
+
+		if ( ! state.items.hasOwnProperty( itemId ) ) {
+			return null;
+		}
+
+		const item = state.items[ itemId ];
+
+		let filteredItem;
+		if ( Array.isArray( fields ) ) {
+			filteredItem = {};
+
+			for ( let f = 0; f < fields.length; f++ ) {
+				// Abort the entire request if a field is missing from the item.
+				// This accounts for the fact that queried items are stored by
+				// stable key without an associated fields query. Other requests
+				// may have included fewer fields properties.
+				const field = fields[ f ];
+				if ( ! item.hasOwnProperty( field ) ) {
+					return null;
+				}
+
+				filteredItem[ field ] = item[ field ];
+			}
+		} else {
+			// If expecting a complete item, validate that completeness, or
+			// otherwise abort.
+			if ( ! state.itemIsComplete[ itemId ] ) {
+				return null;
+			}
+
+			filteredItem = item;
+		}
+
+		items.push( filteredItem );
 	}
 
 	return items;

packages/core-data/src/queried-data/test/get-query-parts.js

@@ -11,6 +11,32 @@ describe( 'getQueryParts', () => {
 			page: 2,
 			perPage: 2,
 			stableKey: '',
+			fields: null,
+			include: null,
+		} );
+	} );
+
+	it( 'parses out `include` ID filtering', () => {
+		const parts = getQueryParts( { include: [ 1 ] } );
+
+		expect( parts ).toEqual( {
+			page: 1,
+			perPage: 10,
+			stableKey: '',
+			fields: null,
+			include: [ 1 ],
+		} );
+	} );
+
+	it( 'parses out `_fields` property filtering', () => {
+		const parts = getQueryParts( { _fields: 'content', a: 1 } );
+
+		expect( parts ).toEqual( {
+			page: 1,
+			perPage: 10,
+			stableKey: 'a=1',
+			fields: [ 'content' ],
+			include: null,
 		} );
 	} );
 
@@ -23,6 +49,8 @@ describe( 'getQueryParts', () => {
 			page: 1,
 			perPage: 10,
 			stableKey: '%3F=%26&b=2',
+			fields: null,
+			include: null,
 		} );
 	} );
 
@@ -33,6 +61,8 @@ describe( 'getQueryParts', () => {
 			page: 1,
 			perPage: 10,
 			stableKey: 'a%5B0%5D=1&a%5B1%5D=2',
+			fields: null,
+			include: null,
 		} );
 	} );
 
@@ -45,6 +75,8 @@ describe( 'getQueryParts', () => {
 			page: 1,
 			perPage: 10,
 			stableKey: 'b=2',
+			fields: null,
+			include: null,
 		} );
 	} );
 
@@ -55,6 +87,8 @@ describe( 'getQueryParts', () => {
 			page: 1,
 			perPage: -1,
 			stableKey: 'b=2',
+			fields: null,
+			include: null,
 		} );
 	} );
 } );