Final Class: JoiningDataProvider

let employee = [
  { id: 1001, departmentId: 2001, managerId: 1011, firstName: "Chris", lastName: "Black", title: "Software Engineer" },
  { id: 1011, departmentId: 2002, managerId: 1021, firstName: "Jenifer", lastName: "Cooper", title: "Manager" },
  { id: 1021, departmentId: 2003, managerId: 1031, firstName: "Kurt", lastName: "Jonhson", title: "VP" },
  { id: 1022, departmentId: 2003, managerId: 1031, firstName: "Mike", lastName: "Chrison", title: "VP", manager: { firstName: "Guangping", lastName: null } }
];
let department = [
  { id: 2001, locationId: 1, VPId: 1021, name: "JET" },
  { id: 2002, locationId: 1, VPId: 1022, name: "Visual Builder" }
];
let location = [
  { id: 1, city: "Redwood City", state: "California" }
];

// initialize basic DataProvider
let dpEmployee = new ArrayDataProvider(employee, { keyAttributes: 'id' });
let dpDepartment = new ArrayDataProvider(department, { keyAttributes: 'id' });
let dpLocation = new ArrayDataProvider(location, { keyAttributes: 'id' });

// join for department
let locJoin = { foreignKeyMapping: { foreignKey: 'locationId' }, joinedDataProvider: dpLocation };
let VPJoin = { foreignKeyMapping: { foreignKey: 'VPId' }, joinedDataProvider: dpEmployee };
let dpJoinDepartment = new JoiningDataProvider(dpDepartment,
  { joins: { location: locJoin, VP: VPJoin } });

let deptJoin = { foreignKeyMapping: { foreignKey: 'departmentId' }, joinedDataProvider: dpJoinDepartment };
let mgrJoin = { foreignKeyMapping: { foreignKey: 'managerId' }, joinedDataProvider: dpEmployee };

this.dpJoinEmployee = new JoiningDataProvider(dpEmployee,
  { joins: { manager: mgrJoin, department: deptJoin } });

// Using joined dataprovider attributes for fetch methods
// The returned fields will include all fields from base data provider and department plus title from manager.
this.dpJoinEmployee.fetchByOffset({ offset: 0, attributes: ['manager.title'] });

Methods

addEventListener(eventType: string, listener: EventListener): void

Add a callback function to listen for a specific event type.

Parameters:

Name	Type	Description
eventType	string	The event type to listen for.
listener	EventListener	The callback function that receives the event notification.

containsKeys(parameters : FetchByKeysParameters<K>) : Promise<ContainsKeysResults<K>>

Check if there are rows containing the specified keys. The resulting key map will only contain keys which were actually found.

Parameters:

Name	Type	Description
parameters	FetchByKeysParameters	contains by key parameters

Since:

• 4.2.0

Returns:

Returns Promise which resolves to ContainsKeysResults.

Type

Promise.<ContainsKeysResults>

Example

Check if keys 1001 and 556 are contained

let keySet = new Set();
keySet.add(1001);
keySet.add(556);

let value = await dataprovider.containsKeys({keys: keySet});
let results = value['results'];
if (results.has(1001)) {
  console.log('Has key 1001');
} else if (results.has(556){
  console.log('Has key 556');
}

createOptimizedKeyMap(initialMap?: Map<K, D>): Map<K, D>

Return an empty Map which is optimized to store key value pairs

Optionally provided by certain DataProvider implementations for storing key/value pairs from the DataProvider in a performant fashion. Sometimes components will need to temporarily store a Map of keys provided by the DataProvider, for example, in the case of maintaining a Map of selected keys. Only the DataProvider is aware of the internal structure of keys such as whether they are primitives, Strings, or objects and how to do identity comparisons. Therefore, the DataProvider can optionally provide a Map implementation which can performantly store key/value pairs surfaced by the DataProvider.

Parameters:

Name	Type	Argument	Description
initialMap	Map.<any>	<optional>	Optionally specify an initial map of key/values for the Map. If not specified, then return an empty Map.

Since:

• 6.2.0

Returns:

Returns a Map optimized for handling keys from the DataProvider.

Type

Map.<any>

Example

create empty key Map

// create optional parameter
let initMap = new Map();
initMap.set('a', 'apple');
let keyMap = dataprovider.createOptimizedKeyMap(initMap);

createOptimizedKeySet(initialSet?: Set<K>): Set<K>

Return an empty Set which is optimized to store keys

Optionally provided by certain DataProvider implementations for storing keys from the DataProvider in a performant fashion. Sometimes components will need to temporarily store a Set of keys provided by the DataProvider, for example, in the case of maintaining a Set of selected keys. Only the DataProvider is aware of the internal structure of keys such as whether they are primitives, Strings, or objects and how to do identity comparisons. Therefore, the DataProvider can optionally provide a Set implementation which can performantly store keys surfaced by the DataProvider.

Parameters:

Name	Type	Argument	Description
initialSet	Set.<any>	<optional>	Optionally specify an initial set of keys for the Set. If not specified, then return an empty Set.

Since:

• 6.2.0

Returns:

Returns a Set optimized for handling keys from the DataProvider.

Type

Set.<any>

Example

create empty key Set

// create optional initial parameter
let initSet = new Set();
initSet.add('a');
let keySet = dataprovider.createOptimizedKeySet(initSet);

dispatchEvent(evt: Event): boolean

Dispatch an event and invoke any registered listeners.

Parameters:

Name	Type	Description
event	Event	The event object to dispatch.

Returns:

Return false if a registered listener has cancelled the event. Return true otherwise.

Type

boolean

fetchByKeys(parameters : FetchByKeysParameters<K>) : Promise<FetchByKeysResults<K, D>>

Fetch rows by keys. The resulting key map will only contain keys which were actually found.

Parameters:

Name	Type	Description
parameters	FetchByKeysParameters	fetch by key parameters

Since:

• 4.2.0

Returns:

Returns Promise which resolves to FetchByKeysResults.

Type

Promise.<FetchByKeysResults>

Example

Fetch for keys 1001 and 556

let keySet = new Set();
keySet.add(1001);
keySet.add(556);

let value = await dataprovider.fetchByKeys({keys: keySet});
// get the data for key 1001
console.log(value.results.get(1001).data);

fetchByOffset(parameters: FetchByOffsetParameters<D>): Promise<FetchByOffsetResults<K, D>>

Fetch rows by offset

A generic implementation of this method is available from FetchByOffsetMixin. It is for convenience and may not provide the most efficient implementation for your data provider. Classes that implement the DataProvider interface are encouraged to provide a more efficient implementation.

Parameters:

Name	Type	Description
parameters	FetchByOffsetParameters	fetch by offset parameters

Since:

• 4.2.0

Returns:

Returns Promise which resolves to FetchByOffsetResults.

Type

Promise.<FetchByOffsetResults>

Example

Fetch by offset 5 rows starting at index 2

let result = await dataprovider.fetchByOffset({size: 5, offset: 2});
let results = result['results'];
let data = results.map(function(value) {
  return value['data'];
});
let keys = results.map(function(value) {
  return value['metadata']['key'];
});

fetchFirst(parameters?: FetchListParameters<D>): AsyncIterable<FetchListResult<K, D>>

Get an AsyncIterable object for iterating the data.

AsyncIterable contains a Symbol.asyncIterator method that returns an AsyncIterator. AsyncIterator contains a “next” method for fetching the next block of data.

The "next" method returns a promise that resolves to an object, which contains a "value" property for the data and a "done" property that is set to true when there is no more data to be fetched. The "done" property should be set to true only if there is no "value" in the result. Note that "done" only reflects whether the iterator is done at the time "next" is called. Future calls to "next" may or may not return more rows for a mutable data source.

Please see the DataProvider documentation for more information on custom implementations.

Parameters:

Name	Type	Argument	Description
params	FetchListParameters	<optional>	fetch parameters

See:

• https://github.com/tc39/proposal-async-iteration for further information on AsyncIterable.

Returns:

AsyncIterable with FetchListResult

Type

AsyncIterable.<FetchListResult>

Example

Get an asyncIterator and then fetch first block of data by executing next() on the iterator. Subsequent blocks can be fetched by executing next() again.

let asyncIterator = dataprovider.fetchFirst(options)[Symbol.asyncIterator]();
let result = await asyncIterator.next();
let value = result.value;
let data = value.data;
let keys = value.metadata.map(function(val) {
  return val.key;
});
// true or false for done
let done = result.done;

getCapability(capabilityName: string): any

Determines whether this DataProvider defines a certain feature.

Parameters:

Name	Type	Description
capabilityName	string	capability name. Defined capability names are: "fetchByKeys", "fetchByOffset", "sort", "fetchCapability" and "filter".

Since:

• 4.2.0

Returns:

capability information or null if undefined

• If capabilityName is "fetchByKeys", returns a FetchByKeysCapability object.
• If capabilityName is "fetchByOffset", returns a FetchByOffsetCapability object.
• If capabilityName is "sort", returns a SortCapability object.
• If capabilityName is "filter", returns a FilterCapability object.
• If capabilityName is "fetchCapability", returns a FetchCapability object.

Type

Object

Example

Check what kind of fetchByKeys is defined.

let capabilityInfo = dataprovider.getCapability('fetchByKeys');
if (capabilityInfo.implementation == 'iteration') {
  // the DataProvider supports iteration for fetchByKeys
  ...

getTotalSize : {Promise.<number>}

Return the total number of rows in this dataprovider

Returns:

Returns a Promise which resolves to the total number of rows. -1 is unknown row count.

Type

Promise.<number>

Example

Get the total rows

let value = await dataprovider.getTotalSize();
if (value == -1) {
  // we don't know the total row count
} else {
  // the total count
  console.log(value);

isEmpty(): 'yes' | 'no' | 'unknown'

Returns a string that indicates if this data provider is empty. Valid values are:

• "yes": this data provider is empty.
• "no": this data provider is not empty.
• "unknown": it is not known if this data provider is empty until a fetch is made.

Since:

• 4.2.0

Returns:

string that indicates if this data provider is empty

Type

"yes" | "no" | "unknown"

Example

Check if empty

let isEmpty = dataprovider.isEmpty();
console.log('DataProvider is empty: ' + isEmpty);

removeEventListener(eventType: string, listener: EventListener): void

Remove a listener previously registered with addEventListener.

Parameters:

Name	Type	Description
eventType	string	The event type that the listener was registered for.
listener	EventListener	The callback function that was registered.

Type Definitions

DataProviderOptions<D, BD>

Deprecated:

Since	Description
10.1.0	Use type Options instead of object for options

Properties:

Name	Type	Description
joins	Record<keyof Omit<D, keyof BD>, DataProviderJoinInfo<D, any, any>>	A map of attribute name to information about DataProviders to join in. The returned data for each row from the joined DataProvider will be merged as an object under the attribute name in the JoiningDataProvider.

Options<D, BD>

Properties:

Name	Type	Description
joins	Record<keyof Omit<D, keyof BD>, DataProviderJoinInfo<D, any, any>>	A map of attribute name to information about DataProviders to join in. The returned data for each row from the joined DataProvider will be merged as an object under the attribute name in the JoiningDataProvider.