I'm wondering if it's possible to build firebase queries dynamically, at the moment I'm using a variable to determine if startAfter should be included or not.

As you can see this is causing duplicate code, for just one variable

export async function fetchUserPhotosPaginated(userId: string, lastUserPhoto?: QueryDocumentSnapshot): Promise<QuerySnapshot> {
    if (lastUserPhoto) {
        return await getDocs(query(
            collection(db, 'photos'),
            orderBy('createdAt', 'desc'),
            startAfter(lastUserPhoto),
            where('user.id', '==', userId),
            limit(5)
        ))
    }

    return await getDocs(query(
        collection(db, 'photos'),
        orderBy('createdAt', 'desc'),
        where('user.id', '==', userId),
        limit(5)
    ))
}

I've tried

• Use startAfter(null), this did not give the intended effect
• assign the query to a variable let q = query(...) to then update that query using q = q.startAfter(...) this also did not work

CodePudding user response：

The second method of adding startAfter conditionally is correct but your syntax to update query is not. Try refactoring the function as shown below:

export async function fetchUserPhotosPaginated(userId: string, lastUserPhoto?: QueryDocumentSnapshot): Promise<QuerySnapshot> {
  // Initial query
  let q = query(collection(db, 'posts'), orderBy('createdAt', 'desc'))
  
  // Add startAfter is lastUserPhoto is present    
  if (lastUserPhoto) q = query(q, startAfter(lastUserPhoto));
  
  // Add remaining conditions
  q = query(q, where('user.id', '==', userId), limit(5)); 

  return await getDocs(q)
}

You can also add all conditions in an array as explained in following answer:

Firestore conditional where clause using Modular SDK v9