从Firebase检索(allpost)数据并使用uid还要检索用户信息 [英] Retrieving (allpost) data from firebase and using uid want to retrieve user information also

问题描述

我想检索所有帖子，然后每个帖子都有一个uid，使用这个uid我想检索用户信息

I want retrieve all post then with each post there is a uid, using this uid i want to retrieve user information

我的代码是这样的，但是在随后的代码块中它不起作用并且状态没有改变

My code is like this but it is not working and state is not changing in then block

getAllPost(){ 
    let allPost = firebase.database().ref("all-post");
    let postAll = [];
    allPost.once("value").then(data => {
      data.forEach(function (childSnapshot) {
        let childData = childSnapshot.val();
        childData.postId = childSnapshot.key;
        let userInfo = firebase.database().ref(`users/${childData.uid}`);
        userInfo.once("value").then(data => {
          childData.userInfo = data;
          postAll.push(childData);        
        })
      })
    }).then(()=>{
      this.setState({ allPost: postAll,loading: false  },);
    }).catch(err => {
      this.setState({ loading: false });
    });
  }

推荐答案

正如Josh所说，您没有处理所有 userInfo.once()调用都是异步的事实.这意味着现在您的 this.setState({allPost:postAll，loading:false}，)调用会在 postAll.push(childData)发生之前触发.通过添加一些 console.log 语句，您应该能够轻松地看到这一点.

As Josh commented, you're not handling the fact that all your userInfo.once() calls are asynchronous. This means that right now your this.setState({ allPost: postAll,loading: false },) call fires before the postAll.push(childData) happen. You should be able to easily see this by adding some console.log statements.

解决方案是使用 Promise.all():

let allPost = firebase.database().ref("all-post");
let postAll = [];
allPost.once("value").then(data => {
  let promises = [];
  data.forEach(function (childSnapshot) {
    let childData = childSnapshot.val();
    childData.postId = childSnapshot.key;
    let userInfo = firebase.database().ref(`users/${childData.uid}`);
    promises.push(
      userInfo.once("value").then(data => {
        childData.userInfo = data;
        postAll.push(childData);        
      })
    })
  })
  return Promise.all(promises);
}).then(()=>{
  this.setState({ allPost: postAll,loading: false },);
}).catch(err => {
  this.setState({ loading: false });
});

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