Working with firebase.firestore() collections - Hemantsaraf08/rollingstones GitHub Wiki

Two ways to add document to collections

  1. Set the data of a document within a collection, explicitly specifying a document identifier: done by using set method 

  await database.'collectionName'.doc(uid).set({
                    email: Email,
                    userId: uid,
                    username: name,
                    createdAt: database.getCurrentTimeStamp(),
                    profileUrl: downloadUrl,
                    postIds: []
   })
  1. Add a new document to a collection. In this case, Cloud Firestore automatically generates the document identifier. done by using add method 

         // Add a new document with a generated id
       const res = await database.'collectionName'.add({//obj goes here
                 name: 'Tokyo',
                 country: 'Japan'
         });
       console.log('Added document with ID: ', res.id);
  1. Update a document in firebase.firestore() i.e. database done by update method 

         // update doc
       await database.'collectionName'.doc('docNamegoesHere/doc id').update({
            keyToUpdate: [...spreadPrev, updatedValue]
         });
       console.log('Added document with ID: ', res.id);
  1. Get/Fetch data from database:
  • using onSnapshot : this gives current content of database collection, we use this real time property of onSnapshot to set our state therefore what happens is that when ever their is a state change, component and its children get re-rendered In our project we use onSnapshot in Feed.js (to setUserData) & Posts.js (to setPosts) Examples below:

       const unsub = database.posts.orderBy('createdAt', 'desc').onSnapshot(querySnapshot => {
            postsArr = [];//emptying postsArr as whenever new vid is put this method is called and 
            //querysnapshot provides info of all vids, therefore, if we dont empty postsArr it will lead to double entry of vids in our array
            querySnapshot.forEach((doc) => {
                console.log(doc.data(), +"  " + doc.id);
                let data = { ...doc.data(), postId: doc.id }
                postsArr.push(data)
            })
            setPosts(postsArr);
        })


      const unsub = database.users.doc(currentUser.uid).onSnapshot((doc) => {
            // You can listen to a document with the onSnapshot() method. An initial call using the callback you provide creates a document snapshot 
                  immediately with the current contents of the single document.
            // Then, each time the contents change, another call updates the document snapshot.
            console.log(doc.data());
            setUserData(doc.data())

        //any change in users.doc by header or uploadvideo will be noticed by onSnapshot and it will run statements in useEffect
        //also will re-render any children of feed component
    })
**using get method** : this is a simple fetch request with no real time monitoring/listener feature, can be used in child/deeper components as we don't want a listener there as child is re-rendered multiple time due to change in parent 
    
        let eachComment=await database.comments.doc(commentId).get()
        commentsArray.push(eachComment.data());
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