不能更改表以添加外键？

Question

Trying to add foreign key on column 'member_id' of projects table which references on primary key 'id' on members table.

Projects Migration

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

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

            $table->timestamps();
        });

Members migration

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 migration

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

Make it unsigned and nullable .

Separate creating a column and adding foreign key logic to avoid similar errors:

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');

});