filtering by child collection

[ahdat81]

Ive tried various things between db rules, queries, etc... not sure what the right approach is. So i have a collection of groups. within each group i have a collection of members (which contains a uid). How do i get back all groups which a user is a member of? I didnt see a way to filter by a collection of child's prop.

I can probably get it by separating groups and members, but its hard to tell what the right approach is.

[appy-one]

Ok, so if I understand it correctly, this is your datamodel:

{
   "groups": {
      "group1": {
          "members": {
             "member1": "user1uuid",
             "member2": "user2uuid",
             "member3": "user3uuid"
          }
      },
      "group2": {
         "members": {
            "member1": "user3uuid"
         }
      }
   }
}

And you'd want to get all groups that, say user "user3uuid" is a member of?

Option 1:

Convert your members collections to arrays:

{
   "groups": {
      "group1": {
          "members": ["user1uuid", "user2uuid", "user3uuid"]
      },
      "group2": {
         "members": ["user3uuid"]
      }
   }
}

You can then create an array index (optional): db.indexes.create('groups', 'members', { type: 'array' }) and query the groups with db.query('groups').filter('members', 'contains', 'user3uuid').get()

Option 2 (more work):

Convert the member strings to objects:

{
   "groups": {
      "group1": {
          "members": {
             "member1": { "uuid": "user1uuid" },
             "member2": { "uuid": "user2uuid" },
             "member3": { "uuid": "user3uuid" }
          }
      },
      "group2": {
         "members": {
            "member1": { "uuid": "user3uuid" }
         }
      }
   }
}

You can then create the index (required): db.indexes.create('groups/*/members', 'uuid'), then:

// Get references to matching member nodes with a query:
const refs = await db.query('groups/$groupId/members').filter('uuid', '==', 'user3uuid').getRefs();

// Extract groupId's from the paths
const groupIds = refs.map(ref => ref.vars.groupId);

// Fetch only the matched groups:
const snapshot = db.ref('groups').get({ include: groupIds });
// snapshot.val() contains { "group1": { ... }, "group2": { ... } }

// Iterate groups:
snapshot.forEach(snap => {
   console.log(`Found group ${snap.ref.key}: `, snap.val());
})

Note: no code above is tested, might contain typos...

Hope this helps!

[ahdat81]

So i was able to get it working, but not exactly in the way its described. Maybe this will help my understand and others that run into this. I think there was a typo of between the index and the query path. They both seem to need to match in order to work, or it will just return an empty result.

db.indexes.create('groups/$groupid/members', 'uid')
db.query('groups/$groupId/members')...

or

db.indexes.create('groups//members', 'uid')
db.query('groups//members')...

next... const groupIds = refs.map(ref => ref.vars.groupid)
i could see that ref.vars is an object but couldn't peer much into it. I tried various ways of extracting something out of it but couldnt get anything. ref.vars.groupid, ref.vars[0], ref.vars['groupid'], ref.vars['id'], etc.. just kept getting undefined. maybe because we are only getRef() that its not populating ref.vars? So to get around this i was able to get the groupid by moving up the parent nodes. final code being:

db.indexes.create('groups//members', 'uid')
...
const refs = await db.query('groups//members').filter('uid', '==', user().uid).getRefs();
const groupIds = refs.map(ref => ref.parent.parent.key)
const snapshot = await db.ref('groups').get({ include: groupIds })
let snaps = snapshot.val()
for(let key in snaps)
this.myGroups.push(snaps[key])

[ahdat81]

awesome appreciate the quick response! thanks for both examples, option two is what i needed (each member object has a bunch of properties with it).