Laravel 关系：实现用户互赞匹配功能的最佳实践

// app/Models/User.php

class User extends Model
{
    // ... 其他属性和方法

    /**
     * 用户喜欢了哪些其他用户
     */
    public function likesToUsers()
    {
        return $this->belongsToMany(self::class, 'users_users_liked', 'user_id', 'user_liked_id');
    }

    /**
     * 哪些其他用户喜欢了当前用户
     */
    public function likesFromUsers()
    {
        return $this->belongsToMany(self::class, 'users_users_liked', 'user_liked_id', 'user_id');
    }

    /**
     * 尝试定义匹配关系 (存在问题)
     */
    public function matches()
    {
        // 这种尝试在预加载时会失败
        return $this->likesFromUsers()->whereIn('user_id', $this->likesToUsers->keyBy('id'));
    }
}

// app/Models/User.php

use Illuminate\Database\Eloquent\Relations\BelongsToMany;
use Illuminate\Database\Query\JoinClause; // 导入 JoinClause

class User extends Model
{
    // ... 其他属性和方法

    public function likesToUsers(): BelongsToMany
    {
        return $this->belongsToMany(self::class, 'users_users_liked', 'user_id', 'user_liked_id');
    }

    public function likesFromUsers(): BelongsToMany
    {
        return $this->belongsToMany(self::class, 'users_users_liked', 'user_liked_id', 'user_id');
    }

    /**
     * 获取当前用户的匹配用户
     * 通过自连接中间表实现互赞逻辑
     */
    public function matches(): BelongsToMany
    {
        return $this->likesFromUsers()
            ->join('users_users_liked as alt_users_users_liked', function (JoinClause $join) {
                $join->on('users_users_liked.user_liked_id', '=', 'alt_users_users_liked.user_id')
                     ->on('users_users_liked.user_id', '=', 'alt_users_users_liked.user_liked_id');
            });
    }
}

Schema::create('users_users_liked', function (Blueprint $table) {
    $table->increments('id');
    $table->unsignedInteger('user_id')->index();
    $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade')->onUpdate('cascade');
    $table->unsignedInteger('user_liked_id')->nullable()->index(); // nullable 可能不是最佳选择
    $table->foreign('user_liked_id')->references('id')->on('users')->onDelete('cascade')->onUpdate('cascade');
    $table->timestamps();
});

// database/migrations/xxxx_xx_xx_create_users_users_liked_table.php

use Illuminate\Database\Migrations\Migration;
use Illuminate\Database\Schema\Blueprint;
use Illuminate\Support\Facades\Schema;

class CreateUsersUsersLikedTable extends Migration
{
    public function up()
    {
        Schema::create('users_users_liked', function (Blueprint $table) {
            $table->id(); // 使用 $table->id() 替代 $table->increments('id')

            // 使用 foreignId() 简化外键定义
            $table->foreignId('user_id')
                  ->constrained('users') // 默认关联到 users 表的 id 字段
                  ->cascadeOnDelete()   // 父记录删除时，子记录也删除
                  ->cascadeOnUpdate();  // 父记录更新时，子记录也更新

            $table->foreignId('user_liked_id')
                  ->constrained('users') // 明确关联到 users 表的 id 字段
                  ->cascadeOnDelete()
                  ->cascadeOnUpdate();

            $table->timestamps();

            // 添加唯一约束，防止重复的喜欢记录
            $table->unique(['user_id', 'user_liked_id']);
        });
    }

    public function down()
    {
        Schema::dropIfExists('users_users_liked');
    }
}

// database/seeders/UserSeeder.php (示例)

use App\Models\User;
use Illuminate\Database\Seeder;

class UserSeeder extends Seeder
{
    public function run()
    {
        // 创建10个用户
        User::factory()->count(10)->create()->each(function ($user) {
            // 让每个用户随机喜欢2-5个其他用户
            $likedUsers = User::inRandomOrder()->limit(rand(2, 5))->where('id', '!=', $user->id)->pluck('id');
            $user->likesToUsers()->attach($likedUsers);
        });

        // 也可以为特定用户设置互赞关系进行测试
        $user1 = User::find(1);
        $user2 = User::find(2);

        if ($user1 && $user2) {
            $user1->likesToUsers()->attach($user2->id); // 用户1喜欢用户2
            $user2->likesToUsers()->attach($user1->id); // 用户2喜欢用户1
        }
    }
}