DataLoader arbitrary queries?

[lorensr]

We could combine queries with an $or like in @pcorey's article:

http://www.petecorey.com/blog/2017/08/21/advanced-mongodb-query-batching-with-dataloader-and-sift/

How useful is that? We'd have fewer network requests to the server, but I imagine the bulk of the work is the query itself, which I don't imagine is actually getting simpler/faster. And memoization is great, but how likely is a repeat arbitrary query? In the case of findById it's clearly a common occurrence.

[ecerroni]

I think it would be useful. I implemented it myself adding this code block to cache.js:

const dataQuery = ({ queries }) => collection.find({ $or: queries })
      .toArray()
      .then(items => queries.map((query) => items.filter(sift(query))));

  const queryLoader = new DataLoader(queries => dataQuery({ queries }))

  // Only batching, no caching atm
  collection.findManyByQuery = async (query) => {
    const docs = await queryLoader.load(query)
    return docs
  }

I also modified cache.test.js:

const now = new Date()
const oneWeekAgo = new Date(now.getFullYear(), now.getMonth(), now.getDate() - 7)

const docs = {
  id1: {
    _id: 'id1',
    createdAt: now
  },
  id2: {
    _id: 'id2',
    createdAt: oneWeekAgo
  },
  id3: {
    _id: 'id3',
    createdAt: oneWeekAgo
  }
}

....


  beforeEach(() => {
    collection = {
      collectionName,
      find: jest.fn((args) => ({
        toArray: () =>
          new Promise(resolve => {
            if (args.$or) {
              const { $or: queries } = args
              const siftDocs = Object.keys(docs).reduce((a, k) => [...a, docs[k]], [])
              setTimeout(() => resolve(queries.reduce((arr, query) => [...arr, ...siftDocs.filter(sift(query))], [])), 0)
            } else {
              const { _id: { $in: ids } } = args
              setTimeout(() => resolve(ids.map(id => docs[id])), 0)
            }            
          })
      }))
    }

    cache = new InMemoryLRUCache()

    setupCaching({ collection, cache })
  })

....

  it('finds two with queries batching', async () => {
    const foundDocs = await collection.findManyByQuery({
      createdAt: { $lte: oneWeekAgo }
    })
    expect(foundDocs[0]).toBe(docs.id2)
    expect(foundDocs[1]).toBe(docs.id3)
    expect(foundDocs.length).toBe(2)

    expect(collection.find.mock.calls.length).toBe(1)
  })