Laravel中的Eloquent關(guān)系用于通過模型連接不同數(shù)據(jù)庫表，簡化關(guān)聯(lián)數(shù)據(jù)操作。一對一關(guān)系如用戶與資料：User模型用hasOne(Profile::class)，Profile模型用belongsTo(User::class)。一對多關(guān)系如文章與評論：Post模型用hasMany(Comment::class)，Comment模型用belongsTo(Post::class)。多對多關(guān)系如用戶與角色：User和Role模型均使用belongsToMany()方法，并通過中間表管理關(guān)系，可用attach()或detach()添加或移除關(guān)聯(lián)。

Eloquent relationships in Laravel are how you connect different database tables using models. They make it easier to work with related data without writing raw SQL joins every time.

One-to-One Relationships

This is when one record in a table is linked to exactly one record in another table.

For example, a User might have one Profile. To set this up in Eloquent:

• You create two models: User and Profile.
• In the User model, define a method called profile() that returns $this->hasOne(Profile::class);
• In the Profile model, define a method called user() that returns $this->belongsTo(User::class);

By default, Eloquent assumes the foreign key is the model’s name in snake_case plus _id, like user_id.

You can then do things like:

$user = User::find(1);
echo $user->profile->bio;

This makes it easy to access related data without manually querying each time.

One-to-Many Relationships

This is when one record has many related records — like a Post having many Comments.

To set this up:

• The Comment model should belong to a Post.
• The Post model should define a method like comments() that returns $this->hasMany(Comment::class);

Then you can fetch all comments for a post easily:

$post = Post::find(5);
foreach ($post->comments as $comment) {
    echo $comment->text;
}

And if a comment has a post_id, you can go the other way too:

$comment = Comment::find(1);
echo $comment->post->title;

It's pretty common to use this for things like blog posts, orders per customer, etc.

Many-to-Many Relationships

This is when multiple records in one table relate to multiple records in another — like Users belonging to multiple Roles, or Posts connected to many Tags.

To handle this, you need a pivot table (like role_user or tag_post). In Eloquent:

• A User model would have a roles() method returning $this->belongsToMany(Role::class);
• And a Role model would have a users() method doing the same back.

Then you can grab related data like:

$user = User::find(1);
foreach ($user->roles as $role) {
    echo $role->name;
}

You can also attach or detach relationships:

• Attach: $user->roles()->attach($roleId);
• Detach: $user->roles()->detach($roleId);

This is super useful when dealing with tags, permissions, categories, and more.

That’s the core idea behind these three Eloquent relationships. They’re not hard once you see how they map real-world connections into code — just remember which model owns the foreign key and how the methods point to each other.

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