Cannot update during an existing state transition when fetching counts - reactjs

Question

I'm trying to fetch post likes, and pass it as a prop to redux.
So i can use it like
myLikes={this.props.myLikes} which renders Likes 6 or whatever the count number is
{this.getLikes(post.Likes)} // retrieves like counts
However i get this warning
Cannot update during an existing state transition (such as within
render). Render methods should be a pure function of props and
state.
My objective is to retrieve likes and map it back to its respected post.
What approach should i use, or am i somewhere in the ballpark ? Cause of now all im getting duplicate values like this
Duplicate values shown here
here is the code
PostList.js
getLikes = (count) => {
this.props.getCount(count)
}
render(){
const {posts} = this.props;
return (
<div>
{posts.map((post, i) => (
<Paper key={post.id} style={Styles.myPaper}>
{this.getLikes(post.Likes)}
{/* {...post} prevents us from writing all of the properties out */}
<PostItem
myLikes={this.props.myLikes}
myTitle={this.state.title}
editChange={this.onChange}
editForm={this.formEditing}
isEditing={this.props.isEditingId === post.id}
removePost={this.removePost}
{...post}
/>
</Paper>
))}
</div>
)
}
}
const mapStateToProps = (state) => ({
isEditingId: state.post.isEditingId,
myLikes: state.post.likes
})
export default connect(mapStateToProps, mapDispatchToProps)(PostList);
Actions.js
export const getCount = (count) => {
return (dispatch) => {
dispatch({type: GET_LIKES_COUNT, count})
}
}
export const GetPosts = () => {
return (dispatch, getState) => {
return Axios.get('/api/posts/myPosts')
.then( (res) => {
const data = res.data
dispatch({type: GET_POSTS, data})
})
}
}
reducer
const initialState = {
post: [],
postError: null,
posts:[],
isEditing:false,
isEditingId:null,
likes:[],
someLike:[],
postId:null
}
export default (state = initialState, action) => {
switch (action.type) {
case GET_POSTS:
return {
...state,
posts: action.data, // maps posts fine
}
case GET_LIKES_COUNT:
console.log(action.count)
return({
...state,
likes: action.count.length
})
Posts.js
import React, { Component } from 'react';
import PostList from './PostList';
import {connect} from 'react-redux';
import { withRouter, Redirect} from 'react-router-dom';
import {GetPosts} from '../actions/';
const Styles = {
myPaper:{
margin: '20px 0px',
padding:'20px'
}
,
wrapper:{
padding:'0px 60px'
}
}
class Posts extends Component {
state = {
posts: [],
loading: true,
isEditing: false,
}
async componentWillMount(){
await this.props.GetPosts();
const thesePosts = await this.props.myPosts
const myPosts2 = await thesePosts
this.setState({
posts: myPosts2,
loading:false
})
console.log(this.state.posts.Likes);
}
render() {
const {loading} = this.state;
const { myPosts} = this.props
if (!this.props.isAuthenticated) {
return (<Redirect to='/signIn' />);
}
if(loading){
return "loading..."
}
return (
<div className="App" style={Styles.wrapper}>
<h1> Posts </h1>
<PostList posts={this.state.posts}/>
</div>
);
}
}
const mapStateToProps = (state) => ({
isAuthenticated: state.user.isAuthenticated,
myPosts: state.post.posts
})
const mapDispatchToProps = (dispatch, state) => ({
GetPosts: () => dispatch( GetPosts())
});
export default withRouter(connect(mapStateToProps,mapDispatchToProps)(Posts));
PostItem.js
import React, { Component } from 'react';
import Paper from '#material-ui/core/Paper';
import Button from '#material-ui/core/Button';
import Typography from '#material-ui/core/Typography';
import moment from 'moment';
import Editable from './Editable';
import {connect} from 'react-redux';
import {UpdatePost, postLike, getCount} from '../actions/';
import Like from './Like';
import Axios from '../Axios';
const Styles = {
myPaper: {
margin: '20px 0px',
padding: '20px'
},
button:{
marginRight:'30px'
}
}
class PostItem extends Component{
constructor(props){
super(props);
this.state = {
disabled: false,
myId: 0,
likes:0
}
}
componentWillMount(){
}
onUpdate = (id, title) => () => {
// we need the id so expres knows what post to update, and the title being that only editing the title.
if(this.props.myTitle !== null){
const creds = {
id, title
}
this.props.UpdatePost(creds);
}
}
render(){
const {title, id, userId, removePost, createdAt, post_content, username, editForm, isEditing, editChange, myTitle, postUpdate, Likes, clickLike, myLikes} = this.props
return(
<div>
<Typography variant="h6" component="h3">
{/* if else teneray operator */}
{isEditing ? (
<Editable editField={myTitle ? myTitle : title} editChange={editChange}/>
): (
<div>
{title}
</div>
)}
</Typography>
<Typography component={'span'} variant={'body2'}>
{post_content}
<h5>by: {username} </h5>
{/* component span cancels out the cant be a decedent of error */}
<Typography component={'span'} variant={'body2'} color="textSecondary">{moment(createdAt).calendar()}</Typography>
{/* gets like counts */}
<Like like={id} likes={myLikes} />
</Typography>
{!isEditing ? (
<Button variant="outlined" type="submit" onClick={editForm(id)}>
Edit
</Button>
):(
// pass id, and myTitle which as we remember myTitle is the new value when updating the title
<div>
<Button
disabled={myTitle.length <= 3}
variant="outlined"
onClick={this.onUpdate(id, myTitle)}>
Update
</Button>
<Button
variant="outlined"
style={{marginLeft: '0.7%'}}
onClick={editForm(null)}>
Close
</Button>
</div>
)}
{!isEditing && (
<Button
style={{marginLeft: '0.7%'}}
variant="outlined"
color="primary"
type="submit"
onClick={removePost(id)}>
Remove
</Button>
)}
</div>
)
}
}
const mapStateToProps = (state) => ({
isEditingId: state.post.isEditingId,
// myLikes: state.post.likes
})
const mapDispatchToProps = (dispatch) => ({
// pass creds which can be called anything, but i just call it credentials but it should be called something more
// specific.
UpdatePost: (creds) => dispatch(UpdatePost(creds)),
postLike: (id) => dispatch( postLike(id)),
// Pass id to the DeletePost functions.
});
export default connect(mapStateToProps, mapDispatchToProps)(PostItem);
Value of action.count
values: 6
values: 0

Answer 1

Your problem is that you're changing the state inside your render method.
{this.getLikes(post.Likes)}
This piece of code leads to an action inside your reducer which then updates the state. That is what redux is all about.
But since react does not allow to change the state while rendering you get your error message. It would eventually lead to an infinite loop when a new state comes up, render didn't finish yet and the new state triggers render again.
What you want to do is put this.state.likes at the place of this.getLikes(post.Likes) and call the latter inside componentDidMount. That way render can finish without bein interrupted. On the first call of render you have to make sure that this.state.likes has a valid value (e.g. null) and on the second render this.state.likes will have the value of the action you trigger with this.getLikes(post.Likes).
For illustration:
render (with this.state.likes = null)
componentDidMount gets called
redux action
this.state.likes changes
render (with this.state.likes = 6)
Read the docs for detailed information about the lifecycle methods.