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| /* Creates a data loader. | |
| Accepts a batch function that should return a promise | |
| that resolves with the list of values fetched for | |
| each of the keys */ | |
| function createLoader(batch) { | |
| const keys = [] | |
| const resolvers = [] | |
| //Here's the magic, accumulate calls and run them on the next tick | |
| process.nextTick(async () => { | |
| console.log('resolving batch for keys:', keys); | |
| const values = await batch(keys); | |
| //Resolver promesas en el orden | |
| resolvers.forEach((res, ix) => { | |
| res(values[ix]) | |
| }); | |
| }); | |
| return { | |
| load(id) { | |
| keys.push(id); | |
| let resolver; | |
| //Create a deferred promise and store the resolve callback in the "resolvers" array | |
| return new Promise((resolve, reject) => { | |
| resolver = resolve; | |
| resolvers.push(resolver); | |
| }) | |
| } | |
| } | |
| } | |
| //Test loading from db | |
| (async () => { | |
| const getBatchRecordsForKeys = async (keys) => { | |
| console.log('Just one DB call needed!') | |
| //Real code would call a store procedure | |
| //or create one query that returns all values for the keys | |
| return keys.map(key => ({ id: key, name: "person " + key })) | |
| } | |
| const loader = createLoader(getBatchRecordsForKeys); | |
| const p1 = loader.load(1); | |
| const p2 = loader.load(2); | |
| const p3 = loader.load(3); | |
| const p4 = loader.load(4); | |
| p1.then((value)=>{console.log(value)}) | |
| p2.then((value)=>{console.log(value)}) | |
| p3.then((value)=>{console.log(value)}) | |
| p4.then((value)=>{console.log(value)}) | |
| })(); | |
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