Question 74884 in Flutter Question posted in
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How to combine two firestore queries in Flutter

I want to combine two firestore queries from the same collection. I want the result combination to be a Query.

var a = lessons
    .withConverter<Lesson>(
      fromFirestore: (snapshot, _) => Lesson.fromFirestore(snapshot),
      toFirestore: (Lesson lesson, options) => lesson.toFirestore(),
    )
    .where('private', isEqualTo: false);

var b = lessons
    .withConverter<Lesson>(
      fromFirestore: (snapshot, _) => Lesson.fromFirestore(snapshot),
      toFirestore: (Lesson lesson, options) => lesson.toFirestore(),
    )
    .where('private', isEqualTo: true)
    .where('author', isEqualTo: uid);

The first query gets all public lessons regardless of the author, the second query only gets the private lessons that the user created. I would then like to combine those results or create a union of the results.

I’m relatively new to flutter firestore, I’ve looked for some solutions online but I couldn’t find one that fits my specific scenario.

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2

Answers


  1. 0 
    var uid = 'your_user_id';

var query = lessons
  .withConverter<Lesson>(
    fromFirestore: (snapshot, _) => Lesson.fromFirestore(snapshot),
    toFirestore: (Lesson lesson, options) => lesson.toFirestore(),
  )
  .where('private', whereIn: [false, true])
  .where('author', isEqualTo: uid);
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  2. 0

    You can use the new OR capabilities of Firestore to put this in a single query. The most literal translation would look like this:

    lessons.where(
  Filter.or(
    Filter("public", isEqualTo: true),
    Filter.and(
      Filter("author", isEqualTo: user.uid),
      Filter("public", isEqualTo: false)
    )
  )
)

    Since your public is a boolean, it can only be true or false, you can rewrite the above to this shorter form:

    lessons.where(
  Filter.or(
    Filter("author", isEqualTo: user.uid),
    Filter("public", isEqualTo: true)
  )
)

    The results for both are guaranteed to be the same, so I’d go for the latter, shorter query.

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