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Add example for Cloud Firestore #268

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Add example for Cloud Firestore #268

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docs: ✏️ Add example for Cloud Firestore
shoNagai May 8, 2021
d8ba705
docs: ✏️ add sorted by key
shoNagai May 15, 2021
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29 changes: 29 additions & 0 deletions examples/CloudFirestore.md
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# Using DataLoader with Cloud Firestore

Cloud Firestore is a "NoSQL" document-oriented database which supports [in operator](https://firebase.google.com/docs/firestore/query-data/queries#in_not-in_and_array-contains-any),
making it can be used with DataLoader.

Here we build an example Cloud Firestore DataLoader using [firebase-admin](https://firebase.google.com/docs/admin/setup?hl=en).

```js
const admin = require("firebase-admin");

admin.initializeApp({
// You need to Initialize the SDK
});

const datastoreLoader = new DataLoader(
async (keys) => {
const snapshot = await admin
.firestore()
.collection(`users`)
.where(admin.firestore.FieldPath.documentId(), `in`, keys)
.get();
return snapshot.docs.map((doc) => ({ ...doc.data(), id: doc.id }));
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Does firestore guarantee the results will be in the same order as the keys input? If you're not sure this is the case, I think it might be safer if this line was something like:

Suggested change
return snapshot.docs.map((doc) => ({ ...doc.data(), id: doc.id }));
return keys.map(key => {
const doc = snapshot.docs.find(doc => doc.id === key);
return doc ? { ...doc.data(), id: doc.id } : null;
});

(Obviously test this works before adopting it; I've never used Firestore.)

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@benjie
Thank you for your review.

As you said, firestore is retrieved in ascending order by document ID by default, so I think sorting by input key is necessary.

I have added the correction and comments.

I have also implemented and confirmed the test in my repository.

},
{
// The in clause of Cloud Firestore is support up to 10 comparison values
maxBatchSize: 10,
}
);
```