Final Class: DeferredDataProvider

// DeferredDataProvider is used in cases where the data for the DataProvider will be
// provided asynchronously. In the example below, let getDeferredData() be any function
// that returns a Promise that will resolve to the final data.
const deferredDataPromise = getDeferredData();

// Create a Promise that will resolve to an ArrayDataProvider containing the resolved data
const dataProviderPromise = deferredDataPromise.then((resolvedData) => {
 return new ArrayDataProvider(resolvedData);
});

// Then create a DeferredDataProvider object with the promise that will resolve to a DataProvider,
// and an implemenation of DataProvider#getCapability.
const dataprovider = new DeferredDataProvider(dataProviderPromise, capabilityFunc);
// or you may pass in ArrayDataProvider's static getCapability function as
const dataprovider = new DeferredDataProvider(dataProviderPromise, ArrayDataProvider.getCapability);

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');
}

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. Fetch can be aborted if an AbortSignal is specified when calling fetchByKeys.

Parameters:

Name	Type	Description
parameters	FetchByKeysParameters	fetch by key parameters

Since:

• 4.2.0

Returns:

Returns Promise which resolves to FetchByKeysResults.

Type

Promise.<FetchByKeysResults>

Examples

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);

How to abort fetchByKeys

// abort on an AbortController instance will abort all requests that are associated
// with the signal from that abortController.
const abortController = new AbortController();
let keySet = new Set();
keySet.add(1001);
keySet.add(556);
// component passes AbortSignal as part of FetchByKeysParameters to fetchByKeys
// on dataProvider
try {
 let value = await dataprovider.fetchByKeys({keys: keySet, signal: abortController.signal});
} catch (err) {
 // if the data fetch has been aborted, retrieving data from the fetched result
 // will be rejected with DOMException named AbortError
 if (err.severity === 'info') {
   // if the data fetch has been aborted from a jet component as a performance concern, an AbortReason will be provided.
   console.log(err.message);
 }
}
// later when abort is desired, component can invoke abort() on the cached
// abort controller to abort any outstanding data retrieval it requested
// on asyncIterator.
if (abort_is_desired) {
  abortController.abort();
}

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

Fetch rows by offset. Fetch can be aborted if an AbortSignal is specified when calling fetchByOffset.

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. If an unsupported matchBy value is included in FetchByOffsetParameters, an error will be thrown.

Since:

• 4.2.0

Returns:

Returns Promise which resolves to FetchByOffsetResults.

Type

Promise.<FetchByOffsetResults>

Examples

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'];
});

How to abort fetchByOffset

// abort on an AbortController instance will abort all requests that are associated
// with the signal from that abortController.
const abortController = new AbortController();
// component passes AbortSignal as part of FetchByOffsetParameters to fetchByOffset
// on dataProvider
try {
 let value = await dataprovider.fetchByOffset({
                 size: 5,
                 offset: 2,
                 signal: abortController.signal
             });
} catch (err) {
 // if the data fetch has been aborted, retrieving data from the fetched result
 // will be rejected with DOMException named AbortError
 if (err.severity === 'info') {
   // if the data fetch has been aborted from a jet component as a performance concern, an AbortReason will be provided.
   console.log(err.message);
 }
}
// later when abort is desired, component can invoke abort() on the cached
// abort controller to abort any outstanding data retrieval it requested
// on asyncIterator.
if (abort_is_desired) {
  abortController.abort();
}

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: "dedup", "eventFiltering", "fetchByKeys", "fetchByOffset", "fetchCapability", "fetchFirst", "filter", and "sort".

Since:

• 4.2.0

Returns:

capability information or null if undefined

• If capabilityName is "dedup", returns a DedupCapability object.
• If capabilityName is "eventFiltering", returns a EventFilteringCapability object.
• If capabilityName is "fetchByKeys", returns a FetchByKeysCapability object.
• If capabilityName is "fetchByOffset", returns a FetchByOffsetCapability object.
• If capabilityName is "fetchCapability", returns a FetchCapability object. (Deprecated since 10.0.0. Use specific fetch capabilityName (fetchByKeys/fetchByOffset/fetchFirst) instead.)
• If capabilityName is "fetchFirst", returns a FetchFirstCapability object.
• If capabilityName is "filter", returns a FilterCapability object.
• If capabilityName is "sort", returns a SortCapability 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.