Firebase equalto dynamic nested child

问题

With a structure of

/archive: {
  $userId: {
    $archiveKey: {
      foo: 1
    },
    ...
  },
  ...
}

Where $userId references a user id and $archiveKey is dynamic, created by .push().

Is it possible to query the archive ref and get all archiveObjects where foo = 1 ? Or do I need to fetch down the whole table, manually dig into $userId and extract the archiveObjects I'm looking for?

回答1:

Firebase queries can nowadays query nested paths, but the paths cannot be dynamic.

So if you know the uid, you can query that user's archives with:

ref.child(authData.uid).orderByChild('foo').equalTo(1).on(...

If you don't know the uid, then you'll have to create a data structure that allows you to do the lookup:

archive_category_to_uids: {
  foo: {
    1: {
      uid1: true,
      uid2: true
    }
  }
}

A more common way is to separate the archives into their own top-level list and have both users and categories refer to that:

users: {
  userId1: {
    archiveKey1: true,
    ...
  },
  ...
},
archives: {
  archiveKey1: {
    foo: 1,
    uid: uid1
  },
  ...
},
archiveCategories: {
  foo: {
    1: {
      archiveKey1: true,
      archiveKey2: true
    }
  }
}

Now you can get find the archives with:

ref.child('archiveCategories/foo/1').once('value', function(keys) {
  keys.forEach(function(key) {
    ref.child('archives').child(key.key()).once('value', function(snapshot) {
      console.log(snapshot.val());
    });
  };
});

This process is called denormalization and is quite common in NoSQL databases. You're modeling the data for how your application needs to consume it. For more on this and other common patterns, I recommend reading this article on NoSQL data modeling.

来源：https://stackoverflow.com/questions/36740657/firebase-equalto-dynamic-nested-child