Laravel雄辩 - 一对多的关系 [英] Laravel eloquent - One to many relationships

问题描述

我刚刚开始使用laravel v3，并试图围绕雄辩的一对多关系围绕创建一个博客，我有一个与类别有多个关系的帖子（每个帖子都链接到一个类别）。

I have just got started with laravel v3 and am trying to wrap my head around eloquent's One-To-Many relationships by creating a blog, I have posts that have a many to one relationship with categories (Each Post is linked to a category).

我有以下表格，包含以下字段：

I have the following tables with the following fields:

帖子：id，title，body，date_created，category_id

posts: id, title, body, date_created, category_id

类别：id，name

我有以下两种模式：

class Category extends Eloquent 
{
    public function posts()
    {
        return $this->has_many('Post');
    }
}

class Post extends Eloquent 
{
    public function categories()
    {
        return $this->belongs_to('Category');
    }
}

我想出了如何通过传递所有的帖子类别ID：

I figured out how to get all posts by passing in a category id:

category::find(2)->posts()->get())

我只需要帮助，了解如何获取所有帖子，并获得相应的类别。所以在一天结束的时候，我可以输出这样的东西：

I just need help on finding out how to get all posts, and get their corrisponding categories. So at the end of the day in the view I can output something like this:

{$post->title} -  Category: {$post->category->name}

感谢任何帮助！ p>

Thanks for any help!

推荐答案

我希望你会发现这些提示很有用。

I hope you will find these tips useful.

模型将类别功能重命名为类别。一个 belongs_to 关系是单数，所以这篇文章有一个，只有一个类别。

On the post model rename the categories function to category. A belongs_to relation is singular, so this post has one and only one category.

关系也有一个短暂的，这种速记语法是有用的，因为它使用起来比较干净，结果被缓存。举个例子：

Relations also have a short hand, this shorthand syntax is useful because it is cleaner to use and the results are cached. Heres an example:

$category = Category::find(1);
foreach($category->posts as post) {
    echo $post->title;
}

现在一个如何获取所有与他们相关类别的帖子的例子： / p>

Now an example of how to get all the posts with their related categories:

$posts = Post::all();
foreach($posts as $post) {
    echo $post->category->name;
}

现在有一件事你会很快注意到，第二个例子是每个帖子的查询都会增加。这被称为N + 1效应。例如，如果您有5个帖子，则将执行一个查询以获取这些帖子。然后在循环中，我们正在执行一个查询来获取类别。这样可以得到6个查询。

Now one thing you will quickly notice when doing this second example is the number of queries increase for each post you have. This is called the N+1 effect. Example, if you have 5 posts, one query will be executed to get those posts. Then in the loop we are executing a query to get the category. This results in 6 total queries.

为了解决这个问题，使用eager加载，将我们的例子中的6个查询减少到2。

To solve this problem, use eager loading, which reduces those 6 queries in our example down to 2.

$posts = Post::with('category')->all();
foreach($posts as $post) {
    echo $post->category->name;
}

我希望有帮助！

这篇关于Laravel雄辩 - 一对多的关系的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！