我正在为我的网站使用YouTube样式（不喜欢）按钮。但是我不知道该怎么做。在我的数据库中，我有两个表帖子（post_id，user_id，描述），likes（like_id，user_id，post_id，like_status）列值。我加入了两个表，并通过user_id得到了值，我只是使用ngFor帖子并实现了ngIf条件，如果user_id在Likes表中，它们可以正常工作。如果在likes表中不存在user_id，我将无法显示按钮，因为我不知道默认状态下按钮的确切条件。任何人都可以帮助我。
我已经尝试了以下解决方案，但是没有用
*ngIf="( (postLikes.length != 0) && (post.user_id == like.user_id) && (post.post_id == like.post_id) && (like.like_status == 'like'))"*ngIf="( (postLikes.length != 0) && (post.user_id == like.user_id) && (post.post_id == like.post_id) && (like.like_status == 'unlike'))"*ngIf="( (postLikes.length == 0) && (post.user_id !== like.user_id) && (post.post_id !== like.post_id) && (like.like_status !== 'unlike'))"
前两个ngIf条件正常，但最后一个ngIf条件无效。
<div class="container" style="width: 100%; height: 100%; ">
<div class="row" style=" margin: 1px; background-color: #fff; border: 2px solid #ada5a5; border-radius: 4px; ">
<!-- ngFor for posts -->
<div class="container" *ngFor="let post of posts; let i = index">
<div class="row" style="border-top: 2px solid #ada5a5;">
<div class="col-md-12 col-md-offset-0" style=" height: auto; ">
<h6> {{post.description}} </h6>
</div>
</div>
<!--ngFor for likes -->
<div class="container" style="border: 0px solid #ada5a5; ">
<div class="row">
<!--like button-->
<div class=" col-4">
<div *ngFor="let like of postLikes; let j = index ">
<div *ngIf="( (postLikes.length != 0) && (post.user_id == like.user_id) && (post.post_id == like.post_id) && (like.like_status == 'like'))">
<button type="button" class="btn btn-success" (click)=likeSubmit(post.user_id,post.post_id)>Like</button><p>liked</p>
</div>
<div *ngIf="( (postLikes.length != 0) && (post.user_id == like.user_id) && (post.post_id == like.post_id) && (like.like_status == 'unlike'))">
<button type="button" class="btn btn-danger" (click)=likeSubmit(post.user_id,post.post_id)>Like</button><p>Disliked</p>
</div>
<div
*ngIf="( (postLikes.length == 0) && (post.user_id != like.user_id) && (post.post_id != like.post_id) && (like.like_status != 'unlike'))">
<button type="button" class="btn btn-warning" (click)=likeSubmit(post.user_id,post.post_id)>Like</button><p>Default</p>
</div>
</div>
</div>
<!-- dislike button -->
<div class=" col-6">
<div class="" *ngFor="let like of postLikes">
<div *ngIf="((post.user_id==like.user_id) && (post.post_id==like.post_id) && (like.like_status=='like'))">
<button type="button" class="btn btn-warning" (click)=likeSubmit(post.user_id,post.post_id)>Dislike</button>
</div>
<div
*ngIf="((post.user_id==like.user_id) && (post.post_id==like.post_id) && (like.like_status=='unlike'))">
<button type="button" class="btn btn-success" (click)=likeSubmit(post.user_id,post.post_id)>Disliked</button>
</div>
</div>
</div>
</div>
</div><!--Like button ends-->
</div>
</div>
</div>
<TypeScript>
export class AppComponent {
title = 'my-app';
name = 'Angular';
posts: any[] =
[{"post_id":4,"user_id":2,"description":" Hi How are you ","created_date":"2019-01-28T12:30:49.000Z"},{"post_id":5,"user_id":2,"description":" Working a Fine ","created_date":"2019-01-28T12:31:20.000Z"},{"post_id":6,"user_id":2,"description":" Hi How are you ......","created_date":"2019-01-28T12:32:15.000Z"},{"post_id":7,"user_id":2,"description":" 4th test post","created_date":"2019-01-29T07:10:37.000Z"},{"post_id":9,"user_id":2,"description":" 5th test post","created_date":"2019-01-31T11:17:31.000Z"},{"post_id":10,"user_id":2,"description":" 6th test post","created_date":"2019-01-31T12:03:54.000Z"},{"post_id":11,"user_id":2,"description":" 7th post post","created_date":"2019-02-08T05:50:02.000Z"},{"post_id":12,"user_id":2,"description":" 8th test post ","created_date":"2019-02-08T06:08:01.000Z"}];
postLikes:any[] =[{"post_id":4,"user_id":2,"like_status":"unlike","like_id":10},{"post_id":5,"user_id":2,"like_status":"like","like_id":9},{"post_id":6,"user_id":2,"like_status":"like","like_id":8},{"post_id":7,"user_id":2,"like_status":"like","like_id":7},{"post_id":9,"user_id":2,"like_status":"like","like_id":11}]
post_id: any;
// likes: Like[];
like_id: number | null ;
like_status: string;
constructor(private http: HttpClient, private formBuilder: FormBuilder){
}
ngOnInit() { }
// Get user details from DB
getPosts(user_id) {
this.userService.getPosts(user_id).subscribe((data) => {
this.posts = data;
},
error => {
return console.log(error);
}
);
}
// join postlikes
getPostLikes(user_id) {
// debugger
this.userService.get_PostLikes(user_id).subscribe((results) => {
this.postLikes = results;
// console.log(results, 'results', this.postLikes, 'likes');
},
error => {
return console.log(error);
}
);
}
我希望ngIf条件在用户表不在likes表中时显示默认按钮。我的stackBlitz链接
https://stackblitz.com/edit/angular-wddupe?file=src%2Fapp%2Fapp.component.ts
最佳答案
这不是一个完整的答案，我只是无法添加评论，所以...
首先，“ postLikes === 0”始终返回False，因为“ postLikes”是一个数组，但是“ 0”是数字类型。
如果要检查数组中是否有任何值，则可以检查其长度
f.e. if（postLikes.length === 0）或更干净的方式if（postLikes.length）
还要了解'=''==''==='和有什么区别，并修复您的其他ngIf语句。
https://www.w3schools.com/js/js_operators.asp
据我了解，您正在获取特定用户喜欢或不喜欢的所有post_id -s，因此请循环遍历postLikes数组，如果没有该特定的post_id，则显示默认的“喜欢”和“不喜欢”按钮。
我也建议重构整个逻辑。
关于mysql - 在ngFor循环内使用ngIf条件实现类似Angular的按钮，我们在Stack Overflow上找到一个类似的问题：https://stackoverflow.com/questions/56037613/