How to apply filter on an array in a collection in firestore

Question

I want to filter out the only content which is book marked by user, the structure of the data is shared below

 this.contentList = afs.collection < Content > ('Content', ref => ref.where('isActive', '==', true) .where("BookmarkedBy.UserID", "==", "hvC2WQL5JJG3Hbq1hxJe") ) .snapshotChanges().map(actions => { return actions.map(a => { const data = a.payload.doc.data() as Content; data.$key = a.payload.doc.id; return { ...data }; }); }); 

I think i'm making mistake here

.where("BookmarkedBy.UserID","==" , "hvC2WQL5JJG3Hbq1hxJe")

Is there any way I can apply filter on array items inside a collection? any help in this regards will be highly appreciated.

Answer 1

{
    title: "My great post",
    categories: [
        "technology",
        "opinion",
        "cats"
    ]
}

With the data structure above, there is no way to perform this query.

Consider this alternative data structure, where each category is the key in a map and all values are true:

{
    title: "My great post",
    categories: {
        "technology": true,
        "opinion": true,
        "cats": true
    }
}

Reference Link