CODEWITHSUNDEEP
reactjsfirebasereact-nativegoogle-cloud-firestore
flaneurx
flaneurx

Reputation: 154

Firestore function to listen for updates

I am a beginner in React native and firestore, and using these to build a kind of social media app, and I have a weird problem(I think I structured the db the wrong way). I want to have a feed, with all posts, no following-based, no nothing. The first time I structured my posts in db like this: users(collection)->user(doc)->thisUserPosts(collection inside doc) - but I couldn't find a way to fetch through all the thisUserPosts from all user(doc) and display them properly.

So I re-structured the db like this: 2 main collection, posts and users. Completely different. In users collection, only docs of users and their data(name, age, etc). In the other, their posts(name, media, desc, AND userId - where userId == the person who created it. userId field from posts collection docs should exist in users collection).

This second approach works just fine. In feed, I only fetch posts. But the problem arrises when I try to open the post(need to have this feature). I need to be able to display on react-navigation header the name of the user, yet I only have details of the post and only userId, which is to no good use.

So I came up with a solution : add a userName field in the posts collection doc, next to userId and simply display that. Now here's the catch: I need to figure a way(in firestore I think) to listen to updates from users collection docs, in case a user updates his name/username(I don't want to showcase the old name). And I don't know if that's possible inside firestore or how. Or is it better to find a different db structure?

TLDR: Need a function in firestore to listen to updates from other collection OR restructuring the db.

Upvotes: 1

Views: 545

Answers (1)

Dharmaraj
Dharmaraj

Reputation: 50830

If you are fetching posts of a single user then you can just set a listener for his document. Make sure that document has no sensitive information that must not be shared with others and is limited to the owner only.

If you are fetching posts from multiple users then you can use in operator:

db.collection("users").where("userID", "in", ["user_id1", "user_id2"])
    .onSnapshot((snapshot) => {
        console.log(snapshot.docs.map(user => user.data()))
    });

If I assume you will be updating the new name in all the user's posts then you can set the listener on the posts document itself but that won't be nice in case all 30 posts fetched are from same user. That'll end up costing 30 reads just to update the same name.

Edit: A simple example of reading a user's posts and listening updates on the user name:

const userID = "my_user_id"

// fetching user's 30 posts
const postsRef = firebase.firebase().collection("posts").where("userID", "==", userID).limit(30)
const postsSnapshot = await postsRef.get()
const postsData = postsSnapshot.docs.map(post => post.data())
// Array of posts data objects

// listening to change in user's name
firebase.firestore().collection("users").doc("user_id")
    .onSnapshot((doc) => {
        console.log("data: ", doc.data());
        const newUsername = doc.data().username
        const updatedPostsData = postsData.map(post => {
          return ({...post, username: newUsername})
        })
    });

Upvotes: 2

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