Delete document by content of a field in Firestore (flutter)

Question

I have a subcollection 'favourites' under my 'users' collection and I would like to delete any of its documents by checking that the field 'prod_id' is isEqualTo prodId

THis is how I create the subcollection & document when a user taps the favourite button:

      _usersCollectionReference
          .doc(userId)
          .collection('favourites')
          .add({'prod_id': prodId});

Now, I want to be able to delete this document

Solution 1

You can also do a check on the collection itself with where logic

const snapshot = await contentRef.where('favouritething','==', favoriteId)
  
  .get().then((querySnapshot)=>{
// return query snapshot 
      return querySnapshot.docs
      // .map(doc => doc.data());

  })

Solution 2

To delete any document you must know it's ID or have a DocumentReference to it. For that you just need to know the userId and fetch documents where prod_id is equal to the product IDs you want to delete.

FirebaseFirestore.instance
  .collection('users')
  .doc(userId)
  .collection('favourites')
  .where('prod_id', whereIn: [...])
  .get()
  .then((snapshot) {
    // ... 
  });

snapshots is a QuerySnapshot and has a property docs which is an array of QueryDocumentSnapshot. You can loop through that array and delete each document by accessing their reference.

For example, deleting first document in that would be:

snapshot.docs[0].reference.delete()

Comments

[William Chidube]

Perhaps I wasn't clear enough. Passing the userId isn't sufficient to know which specific favourite document to delete. To know this, I need to check one of the fields of the favourite document which is where I store the productId and see that it is equal to the prodId received. In other words I (think) have to query the favourite collection/document for the value of a particular field and if that value is equal to the value I received from the onTap, I can then delete that document.

[chris burd]

I understand what you want to do give me a second and I will update the answer above.

[William Chidube]

Okay thanks. I'll try this out immediately and update you asap.

[chris burd]

this won't be exact William no ones answer will be but it will be very close to what you want - the idea is to loop through each document on a collection and if it matched your variable either let var or const - then it will delete that item. Just be careful if this is a very large collection it can be expensive. you can further refine this by using ref and where on the collection query if you wanted too as well.

[William Chidube]

This is understood, Chris

[Dharmaraj]

This answer uses Javascript but should be good to clarify the same.