417 lines
13 KiB
JavaScript
417 lines
13 KiB
JavaScript
"use strict";
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/**
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* Copyright (c) 2019-present, GraphQL Foundation
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*
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* This source code is licensed under the MIT license found in the
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* LICENSE file in the root directory of this source tree.
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*
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*
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*/
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// A Function, which when given an Array of keys, returns a Promise of an Array
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// of values or Errors.
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// Optionally turn off batching or caching or provide a cache key function or a
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// custom cache instance.
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// If a custom cache is provided, it must be of this type (a subset of ES6 Map).
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/**
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* A `DataLoader` creates a public API for loading data from a particular
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* data back-end with unique keys such as the `id` column of a SQL table or
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* document name in a MongoDB database, given a batch loading function.
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*
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* Each `DataLoader` instance contains a unique memoized cache. Use caution when
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* used in long-lived applications or those which serve many users with
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* different access permissions and consider creating a new instance per
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* web request.
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*/
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var DataLoader =
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/*#__PURE__*/
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function () {
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function DataLoader(batchLoadFn, options) {
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if (typeof batchLoadFn !== 'function') {
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throw new TypeError('DataLoader must be constructed with a function which accepts ' + ("Array<key> and returns Promise<Array<value>>, but got: " + batchLoadFn + "."));
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}
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this._batchLoadFn = batchLoadFn;
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this._maxBatchSize = getValidMaxBatchSize(options);
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this._batchScheduleFn = getValidBatchScheduleFn(options);
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this._cacheKeyFn = getValidCacheKeyFn(options);
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this._cacheMap = getValidCacheMap(options);
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this._batch = null;
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} // Private
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var _proto = DataLoader.prototype;
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/**
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* Loads a key, returning a `Promise` for the value represented by that key.
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*/
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_proto.load = function load(key) {
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if (key === null || key === undefined) {
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throw new TypeError('The loader.load() function must be called with a value,' + ("but got: " + String(key) + "."));
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}
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var batch = getCurrentBatch(this);
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var cacheMap = this._cacheMap;
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var cacheKey = this._cacheKeyFn(key); // If caching and there is a cache-hit, return cached Promise.
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if (cacheMap) {
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var cachedPromise = cacheMap.get(cacheKey);
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if (cachedPromise) {
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var cacheHits = batch.cacheHits || (batch.cacheHits = []);
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return new Promise(function (resolve) {
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cacheHits.push(function () {
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return resolve(cachedPromise);
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});
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});
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}
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} // Otherwise, produce a new Promise for this key, and enqueue it to be
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// dispatched along with the current batch.
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batch.keys.push(key);
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var promise = new Promise(function (resolve, reject) {
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batch.callbacks.push({
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resolve: resolve,
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reject: reject
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});
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}); // If caching, cache this promise.
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if (cacheMap) {
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cacheMap.set(cacheKey, promise);
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}
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return promise;
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}
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/**
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* Loads multiple keys, promising an array of values:
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*
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* var [ a, b ] = await myLoader.loadMany([ 'a', 'b' ]);
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*
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* This is similar to the more verbose:
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*
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* var [ a, b ] = await Promise.all([
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* myLoader.load('a'),
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* myLoader.load('b')
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* ]);
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*
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* However it is different in the case where any load fails. Where
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* Promise.all() would reject, loadMany() always resolves, however each result
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* is either a value or an Error instance.
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*
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* var [ a, b, c ] = await myLoader.loadMany([ 'a', 'b', 'badkey' ]);
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* // c instanceof Error
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*
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*/
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;
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_proto.loadMany = function loadMany(keys) {
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if (!isArrayLike(keys)) {
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throw new TypeError('The loader.loadMany() function must be called with Array<key> ' + ("but got: " + keys + "."));
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} // Support ArrayLike by using only minimal property access
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var loadPromises = [];
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for (var i = 0; i < keys.length; i++) {
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loadPromises.push(this.load(keys[i])["catch"](function (error) {
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return error;
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}));
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}
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return Promise.all(loadPromises);
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}
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/**
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* Clears the value at `key` from the cache, if it exists. Returns itself for
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* method chaining.
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*/
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;
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_proto.clear = function clear(key) {
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var cacheMap = this._cacheMap;
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if (cacheMap) {
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var cacheKey = this._cacheKeyFn(key);
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cacheMap["delete"](cacheKey);
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}
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return this;
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}
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/**
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* Clears the entire cache. To be used when some event results in unknown
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* invalidations across this particular `DataLoader`. Returns itself for
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* method chaining.
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*/
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;
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_proto.clearAll = function clearAll() {
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var cacheMap = this._cacheMap;
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if (cacheMap) {
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cacheMap.clear();
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}
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return this;
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}
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/**
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* Adds the provided key and value to the cache. If the key already
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* exists, no change is made. Returns itself for method chaining.
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*
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* To prime the cache with an error at a key, provide an Error instance.
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*/
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;
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_proto.prime = function prime(key, value) {
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var cacheMap = this._cacheMap;
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if (cacheMap) {
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var cacheKey = this._cacheKeyFn(key); // Only add the key if it does not already exist.
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if (cacheMap.get(cacheKey) === undefined) {
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// Cache a rejected promise if the value is an Error, in order to match
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// the behavior of load(key).
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var promise;
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if (value instanceof Error) {
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promise = Promise.reject(value); // Since this is a case where an Error is intentionally being primed
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// for a given key, we want to disable unhandled promise rejection.
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promise["catch"](function () {});
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} else {
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promise = Promise.resolve(value);
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}
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cacheMap.set(cacheKey, promise);
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}
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}
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return this;
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};
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return DataLoader;
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}(); // Private: Enqueue a Job to be executed after all "PromiseJobs" Jobs.
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//
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// ES6 JavaScript uses the concepts Job and JobQueue to schedule work to occur
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// after the current execution context has completed:
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// http://www.ecma-international.org/ecma-262/6.0/#sec-jobs-and-job-queues
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//
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// Node.js uses the `process.nextTick` mechanism to implement the concept of a
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// Job, maintaining a global FIFO JobQueue for all Jobs, which is flushed after
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// the current call stack ends.
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//
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// When calling `then` on a Promise, it enqueues a Job on a specific
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// "PromiseJobs" JobQueue which is flushed in Node as a single Job on the
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// global JobQueue.
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//
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// DataLoader batches all loads which occur in a single frame of execution, but
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// should include in the batch all loads which occur during the flushing of the
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// "PromiseJobs" JobQueue after that same execution frame.
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//
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// In order to avoid the DataLoader dispatch Job occuring before "PromiseJobs",
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// A Promise Job is created with the sole purpose of enqueuing a global Job,
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// ensuring that it always occurs after "PromiseJobs" ends.
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//
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// Node.js's job queue is unique. Browsers do not have an equivalent mechanism
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// for enqueuing a job to be performed after promise microtasks and before the
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// next macrotask. For browser environments, a macrotask is used (via
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// setImmediate or setTimeout) at a potential performance penalty.
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var enqueuePostPromiseJob = typeof process === 'object' && typeof process.nextTick === 'function' ? function (fn) {
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if (!resolvedPromise) {
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resolvedPromise = Promise.resolve();
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}
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resolvedPromise.then(function () {
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return process.nextTick(fn);
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});
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} : setImmediate || setTimeout; // Private: cached resolved Promise instance
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var resolvedPromise; // Private: Describes a batch of requests
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// Private: Either returns the current batch, or creates and schedules a
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// dispatch of a new batch for the given loader.
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function getCurrentBatch(loader) {
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// If there is an existing batch which has not yet dispatched and is within
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// the limit of the batch size, then return it.
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var existingBatch = loader._batch;
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if (existingBatch !== null && !existingBatch.hasDispatched && existingBatch.keys.length < loader._maxBatchSize && (!existingBatch.cacheHits || existingBatch.cacheHits.length < loader._maxBatchSize)) {
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return existingBatch;
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} // Otherwise, create a new batch for this loader.
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var newBatch = {
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hasDispatched: false,
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keys: [],
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callbacks: []
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}; // Store it on the loader so it may be reused.
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loader._batch = newBatch; // Then schedule a task to dispatch this batch of requests.
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loader._batchScheduleFn(function () {
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return dispatchBatch(loader, newBatch);
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});
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return newBatch;
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}
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function dispatchBatch(loader, batch) {
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// Mark this batch as having been dispatched.
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batch.hasDispatched = true; // If there's nothing to load, resolve any cache hits and return early.
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if (batch.keys.length === 0) {
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resolveCacheHits(batch);
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return;
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} // Call the provided batchLoadFn for this loader with the batch's keys and
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// with the loader as the `this` context.
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var batchPromise = loader._batchLoadFn(batch.keys); // Assert the expected response from batchLoadFn
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if (!batchPromise || typeof batchPromise.then !== 'function') {
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return failedDispatch(loader, batch, new TypeError('DataLoader must be constructed with a function which accepts ' + 'Array<key> and returns Promise<Array<value>>, but the function did ' + ("not return a Promise: " + String(batchPromise) + ".")));
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} // Await the resolution of the call to batchLoadFn.
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batchPromise.then(function (values) {
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// Assert the expected resolution from batchLoadFn.
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if (!isArrayLike(values)) {
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throw new TypeError('DataLoader must be constructed with a function which accepts ' + 'Array<key> and returns Promise<Array<value>>, but the function did ' + ("not return a Promise of an Array: " + String(values) + "."));
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}
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if (values.length !== batch.keys.length) {
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throw new TypeError('DataLoader must be constructed with a function which accepts ' + 'Array<key> and returns Promise<Array<value>>, but the function did ' + 'not return a Promise of an Array of the same length as the Array ' + 'of keys.' + ("\n\nKeys:\n" + String(batch.keys)) + ("\n\nValues:\n" + String(values)));
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} // Resolve all cache hits in the same micro-task as freshly loaded values.
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resolveCacheHits(batch); // Step through values, resolving or rejecting each Promise in the batch.
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for (var i = 0; i < batch.callbacks.length; i++) {
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var value = values[i];
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if (value instanceof Error) {
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batch.callbacks[i].reject(value);
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} else {
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batch.callbacks[i].resolve(value);
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}
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}
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})["catch"](function (error) {
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return failedDispatch(loader, batch, error);
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});
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} // Private: do not cache individual loads if the entire batch dispatch fails,
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// but still reject each request so they do not hang.
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function failedDispatch(loader, batch, error) {
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// Cache hits are resolved, even though the batch failed.
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resolveCacheHits(batch);
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for (var i = 0; i < batch.keys.length; i++) {
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loader.clear(batch.keys[i]);
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batch.callbacks[i].reject(error);
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}
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} // Private: Resolves the Promises for any cache hits in this batch.
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function resolveCacheHits(batch) {
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if (batch.cacheHits) {
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for (var i = 0; i < batch.cacheHits.length; i++) {
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batch.cacheHits[i]();
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}
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}
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} // Private: given the DataLoader's options, produce a valid max batch size.
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function getValidMaxBatchSize(options) {
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var shouldBatch = !options || options.batch !== false;
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if (!shouldBatch) {
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return 1;
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}
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var maxBatchSize = options && options.maxBatchSize;
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if (maxBatchSize === undefined) {
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return Infinity;
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}
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if (typeof maxBatchSize !== 'number' || maxBatchSize < 1) {
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throw new TypeError("maxBatchSize must be a positive number: " + maxBatchSize);
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}
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return maxBatchSize;
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} // Private
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function getValidBatchScheduleFn(options) {
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var batchScheduleFn = options && options.batchScheduleFn;
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if (batchScheduleFn === undefined) {
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return enqueuePostPromiseJob;
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}
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if (typeof batchScheduleFn !== 'function') {
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throw new TypeError("batchScheduleFn must be a function: " + batchScheduleFn);
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}
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return batchScheduleFn;
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} // Private: given the DataLoader's options, produce a cache key function.
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function getValidCacheKeyFn(options) {
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var cacheKeyFn = options && options.cacheKeyFn;
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if (cacheKeyFn === undefined) {
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return function (key) {
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return key;
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};
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}
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if (typeof cacheKeyFn !== 'function') {
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throw new TypeError("cacheKeyFn must be a function: " + cacheKeyFn);
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}
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return cacheKeyFn;
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} // Private: given the DataLoader's options, produce a CacheMap to be used.
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function getValidCacheMap(options) {
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var shouldCache = !options || options.cache !== false;
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if (!shouldCache) {
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return null;
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}
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var cacheMap = options && options.cacheMap;
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if (cacheMap === undefined) {
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return new Map();
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}
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if (cacheMap !== null) {
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var cacheFunctions = ['get', 'set', 'delete', 'clear'];
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var missingFunctions = cacheFunctions.filter(function (fnName) {
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return cacheMap && typeof cacheMap[fnName] !== 'function';
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});
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if (missingFunctions.length !== 0) {
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throw new TypeError('Custom cacheMap missing methods: ' + missingFunctions.join(', '));
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}
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}
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return cacheMap;
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} // Private
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function isArrayLike(x) {
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return typeof x === 'object' && x !== null && typeof x.length === 'number' && (x.length === 0 || x.length > 0 && Object.prototype.hasOwnProperty.call(x, x.length - 1));
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}
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module.exports = DataLoader; |