Detailed explanation of how to implement multi-table query and paging functions in Laravel

As web development becomes more and more complex, single-table data query cannot meet actual needs. Therefore, in the actual development process, multi-table query has gradually become an indispensable part. In Laravel, multi-table queries can be simplified with a simplicity not found in other ORMs.

In Laravel, multi-table queries can use some related model methods. These methods are simple and easy to use, and can quickly allow us to perform multi-table queries. This article will introduce the multi-table query and paging functions in Laravel.

Multi-table query

Multi-table query in Laravel can be implemented by using some related model methods provided by Eloquent ORM. These methods allow us to join multiple tables in the database and perform joint queries.

One-to-one connection

One-to-one connection is the easiest type of relational database. In Laravel, you can join two tables by using the hasOne and belongsTo methods.

Suppose we have a users table and an addresses table, and each user has an address. In this case, we can use the following code to access the user's address:

// 定义 User 模型
class User extends Model
{
    public function address()
    {
        return $this->hasOne(Address::class);
    }
}

// 定义 Address 模型
class Address extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

// 查询
$user = User::find(1);
$address = $user->address; // 返回用户的地址信息

We can also reverse the query:

$address = Address::find(1);
$user = $address->user; // 返回地址所属的用户信息

One-to-many connection

Another A common connection type is a one-to-many connection. In this case, a model can have multiple related models. For example, in a blogging application, a user can have multiple posts. We can use hasMany and belongsTo methods to achieve this type of connection.

// 定义 User 模型
class User extends Model
{
    public function posts()
    {
        return $this->hasMany(Post::class);
    }
}

// 定义 Post 模型
class Post extends Model
{
    public function user()
    {
        return $this->belongsTo(User::class);
    }
}

// 查询
$user = User::find(1);
$posts = $user->posts; // 返回用户的所有文章

We can also add other query conditions in the Post model:

$user = User::find(1);
$posts = $user->posts()->where('published', 1)->get(); // 返回已发布的文章

Many-to-many connection

Many-to-many connection is to connect two models, each model You can have multiple models associated with it. For example, a blog post can have multiple tags, and a tag can be used in multiple posts. In Laravel, you can join two tables by using belongsToMany method.

// 定义 Post 模型
class Post extends Model
{
    public function tags()
    {
        return $this->belongsToMany(Tag::class);
    }
}

// 定义 Tag 模型
class Tag extends Model
{
    public function posts()
    {
        return $this->belongsToMany(Post::class);
    }
}

// 查询
$post = Post::find(1);
$tags = $post->tags; // 返回文章的所有标签

We can also add other query conditions to the Tag model:

$tag = Tag::find(1);
$posts = $tag->posts()->where('published', 1)->get(); // 返回该标签下已发布的文章

Paging function

Laravel also provides a paging function that allows us to paginate the query results. . We can use the paginate method to implement the paging function. The paginate method will return a paginator instance, which contains the data of the current page, paging links and other information.

$posts = Post::paginate(10); // 查询所有文章，每页显示 10 条数据

We can also use the auxiliary function links to get the paging link:

{!! $posts->links() !!}

This will display a paginator on the page, and we can click on the page number to switch to different pages.

Multiple table query paging

In the actual development process, we often need to perform joint queries on multiple tables and perform paging according to specific conditions. In Laravel, we can use the following steps to implement multi-table query paging function:

1. Define related models and their methods.
2. Write query code and use the join method to join multiple tables.
3. Use the select method to select the queried data.
4. Use the orderBy method to sort the query results.
5. Use the paginate method to paginate query results.

For example, we have an article management system that contains three tables: posts, categories and tags. The following is the relevant model definition:

// 定义 Post 模型
class Post extends Model
{
    public function category()
    {
        return $this->belongsTo(Category::class);
    }

    public function tags()
    {
        return $this->belongsToMany(Tag::class);
    }
}

// 定义 Category 模型
class Category extends Model
{
    public function posts()
    {
        return $this->hasMany(Post::class);
    }
}

// 定义 Tag 模型
class Tag extends Model
{
    public function posts()
    {
        return $this->belongsToMany(Post::class);
    }
}

We need to query all published articles and sort them from new to old according to the publication time. The query results should include information such as the article's title, author, publication time, classification, and tags. We can use the following code to achieve this:

$posts = Post::join('categories', 'posts.category_id', '=', 'categories.id')
    ->join('post_tag', 'posts.id', '=', 'post_tag.post_id')
    ->join('tags', 'tags.id', '=', 'post_tag.tag_id')
    ->where('posts.published', true)
    ->select(
        'posts.title', 
        'posts.author',
        'posts.published_at',
        'categories.name as category',
        DB::raw('GROUP_CONCAT(tags.name) as tags')
    )
    ->orderBy('published_at', 'desc')
    ->groupBy('posts.id')
    ->paginate(10);

In the above code, we use the join method to join posts, categories and tags Three tables. The conditions of the query (published articles) are specified using the where method. Use the select method to select the fields that need to be queried, and use the GROUP_CONCAT function to combine multiple tags of the same article into one string.

At the end, we use the paginate method for pagination, and the links method in the view file to render the paginator. Complete paging code:

<div>
    <div>
        @foreach ($posts as $post)
        <div>
            <h3 id="post-gt-title">{{ $post->title }}</h3>
            <p>{{ $post->published_at->diffForHumans() }} | {{$post->category}} | Tags: {{ $post->tags }}</p>
            <p>{{ Str::limit($post->content, 200) }}</p>
            <hr>
        </div>
        @endforeach
    </div>
    {{ $posts->links() }}
</div>

Summary: In Laravel, multi-table queries can be implemented using the associated model method, and the paging function can be implemented using the paginate method. Using these functions, we can perform complex data query and processing more conveniently.

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