不能更改表以添加外鍵？

Question

嘗試在項目表的“member_id”列上添加外鍵，該表引用成員表上的主鍵“id”。

項目遷移

Schema::create('projects', function (Blueprint $table) {
            $table->bigIncrements('id');

            $table->text('title');
            $table->text('description');

            $table->timestamps();
        });

會員遷移

Schema::create('members', function (Blueprint $table) {
            $table->bigIncrements('id');
            $table->unsignedBigInteger('country_id');
            $table->string('name');
            $table->string('email');
            $table->integer('active');
            $table->timestamps();
        });

AddMemberIdToProjects 遷移

Schema::table('projects', function (Blueprint $table) {

            $table->unsignedBigInteger('member_id');

            $table->foreign('member_id')->references('id')->on('members');

        });

ERROR 1452 (23000): Cannot add or update a child row: a foreign key constraint fails 

Answer 1

使其unsigned和nullable 。

分開創建列和添加外鍵邏輯，避免類似錯誤：

Schema::table('projects', function (Blueprint $table) {

   $table->unsignedBigInteger('member_id')->nullable();
});

Schema::table('projects', function (Blueprint $table) {
   $table->foreign('member_id')->references('id')->on('members');

});