Firebase query of child key

Question

I have the next structure in my firebase database:

{
    events: {
       event_1:{
           startdate: 120934210,
           enddate: 120934211,
           members: {
               uid_1: true,
               uid_2: true,
               ...
           }
       },
       event_2:{
           startdate: 120934210,
           enddate: 120934211,
           members: {
               uid_2: true,
               uid_3: true,
               ...
           }
       },
       ...
    }
}

I have a node event and every child is an event, each event have a list of members. The question is, how can I do a query for all events of a certain member? For example, all events with member uid_2. I'm using angularfire2 and angular 4. I'm trying to do something like that:

db.list('events/',ref => ref.orderByChild('members').equalTo(uid))

please help me.

try db.list('events/',ref => ref.orderByChild('members/'+uid).equalTo(true)). — Hareesh
– Hareesh, Commented Dec 20, 2017 at 8:21

Frank van Puffelen · Accepted Answer · 2017-12-20 18:58:33Z

1

Your current data structure allows you to easily find the members of a specific event. If does not allow you to easily determine the events for a specific user. To allow that, you should add an inverted data structure.

It is also recommended to not nest different entity types, but instead store them in top-level nodes.

For your data this leads to four likely top-level nodes:

users: {
  $uid: { ... }
},
events: }
  $eventid: { ... }
},
event_users: {
  $event_id: {
    $uid: true
  }
},
user_events: {
  $uid: {
    $event_id: true
  }
}

Now you can easily read (without querying) the members for an event, and the events for a user.

I also recommend you check out:

This great article on NoSQL data modeling
Many to Many relationship in Firebase
http://stackoverflow.com/questions/40656589
The Firebase for SQL developers video series

edited Dec 20, 2017 at 18:58

answered Dec 20, 2017 at 15:06

Frank van Puffelen

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3 Comments

Roberto Salazar Over a year ago

yes that'a a better structure for finding the event_user relation and the user_event relation, but i'll need to read the database more than one time. Is there any way to read all information at once? thanks for your help.

Frank van Puffelen Over a year ago

You'll need to read from each top-level node separately. While it's a bit messy in code, it's not as slow as you may expect since Firebase pipelines the requests. See stackoverflow.com/questions/35931526/…

Roberto Salazar Over a year ago

thanks man, i'll read the NoSQL data modeling. I'm new at nosql databases and sometimes it is a little messy. You saved me thanks.

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