Laravel口才相当复杂的关系

// User.php
public function profile()
{
    return $this->hasOne(Profile::class);
}

// Profile.php
public function user()
{
    return $this->belongsTo(User::class);
}

// User.php
public function posts()
{
    return $this->hasMany(Post::class);
}

// Post.php
public function user()
{
    return $this->belongsTo(User::class);
}

// Role.php
public function users()
{
    return $this->belongsToMany(User::class);
}

// User.php
public function roles()
{
    return $this->belongsToMany(Role::class);
}

// Country.php
public function users()
{
    return $this->hasManyThrough(User::class, City::class);
}

// Comment.php
public function commentable()
{
    return $this->morphTo();
}

// Post.php
public function comments()
{
    return $this->morphMany(Comment::class, 'commentable');
}

// Video.php
public function comments()
{
    return $this->morphMany(Comment::class, 'commentable');
}

// Tag.php
public function models()
{
    return $this->morphedByMany(Model::class, 'taggable');
}

// Model.php
public function tags()
{
    return $this->morphToMany(Tag::class, 'taggable');
}

$users = User::with('posts')->get();
foreach ($users as $user) {
    // 不会触发 N+1 查询
    $user->posts;
}

$users = User::all();
$user->posts; // 只有在访问时才会加载

$users = User::with(['posts' => function ($query) {
    $query->orderBy('created_at', 'desc');
}])->get();