尝试使用Laravel迁移添加外键约束时出错

我试图找出外键,但在添加后尝试迁移时: $table->foreign('user_id')->references('id')->on('users')->onDelete('cascade'); 对于我的代码,我得到以下错误:

"SQLSTATE[HY000]: General error: 1215 Cannot add foreign key constraint (SQL
  : alter table `images` add constraint `images_user_id_foreign` foreign key
  (`user_id`) references `users` (`id`) on delete cascade)
"

用户迁移:

Schema::create('users', function (Blueprint $table) {
                $table->increments('id');
                $table->string('first_name');
                $table->string('last_name');
                $table->string('username');
                $table->string('password');
                $table->string('email');
                $table->string('profile_picture')->nullable()->default('image');
                $table->timestamps();
                $table->rememberToken();
                $table->engine = 'InnoDB';
            });

图像迁移:

Schema::create('images', function (Blueprint $table) {
            $table->increments('id');
            $table->string('name');
            $table->string('description')->nullable()->default(null);
            $table->integer('user_id');
            $table->foreign('user_id')
                  ->references('id')
                  ->on('users')
                  ->onDelete('cascade');
            $table->string('file_name');
            $table->string('upvotes')->default(0);
            $table->string('downvotes')->default(0);
            $table->string('views')->default(0);
            $table->timestamps();
            $table->engine = 'InnoDB';
        });