How to query one field then order by another one in Firebase cloud Firestore?

Question

I'm struggling to make a (not so) complex query in firebase cloud firestore.

I simply need to get all docs where the id field == a given id.

Then order the results by their date and limit to 10 results.

So this is my current situation

db.firestore().collection('comments')
        .where("postId",'==',idOfThePost)
        .orderBy('date','asc').limit(10).get().then( snapshot => {
           //Nothing happens and the request wasn't even been executed
         })

I can get the result only if i don't use the orderBy query but i have to process this sorting for the needs of my application.

Someone has an idea to help me to fix this ?

thanks

Answer 1

You can do this by creating an Index in the firestore.

The first field of the index should be the equality field and the second field of the index should be the order by field.

Given your problem, you would need the following index:

first field: postId, 'asc'
second field: date, 'asc'

Answer 2

Please check the doc. It says

However, if you have a filter with a range comparison (<, <=, >, >=), your first ordering must be on the same field

you can try this code

db.firestore().collection('comments')
    .where("postId",'==',idOfThePost)
    .orderBy('postId')
    .orderBy('date','asc').limit(10).get().then( snapshot => {
       .....
     })