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【Laravel】外部キー制約を外して削除したいのにCan't DROPエラーが出る

Posted at

環境

Laravel v9.5.1 (PHP v8.1.3)

状況

  • PointWalletテーブル
    外部キー:user_id
  • Userテーブル

PointWalletテーブルの外部キーuser_idを一旦削除してcascadeOnDelete()をつけたい。

public function up()
{
    Schema::table('point_wallets', function (Blueprint $table) {
        //外部キーを外す
        $table->dropForeign('point_wallets_user_id_foreign');
        //カラムを落とす
        $table->dropColumn('user_id');
    });
    Schema::table('point_wallets', function (Blueprint $table) {
        $table->foreignId('user_id')->constrained()->cascadeOnDelete();
    });
}

下記のエラーでmigration失敗する。

 Syntax error or access violation: 1091 Can't DROP 'point_wallets_user_id_foreign'; check that column/key exists (SQL: alter table `point_wallets` drop foreign key `point_wallets_user_id_foreign`)

原因と解決法

テーブル作成当初から外部キーを張っていて途中でテーブル名を変えた場合、作成当初のテーブル名を使ったカラム名で指定しないとmigrationに失敗する。
(PointWalletテーブルは以前UserPointテーブルだった)

Schema::table('point_wallets', function (Blueprint $table) {
    //外部キーを外す
    Schema::disableForeignKeyConstraints();
    $table->dropColumn('user_id');
});

disableForeignKeyConstraintsを使うと当初のカラム名がエラー文に出てくれる。

 Cannot drop column 'user_id': needed in a foreign key constraint 'user_points_user_id_foreign' (SQL: alter table `point_wallets` drop `user_id`)

↑を指定してdropForeignするとmigration成功。

public function up()
{
    Schema::table('point_wallets', function (Blueprint $table) {
        $table->dropForeign('user_points_user_id_foreign');
        $table->dropColumn('user_id');
    });
    Schema::table('point_wallets', function (Blueprint $table) {
        $table->foreignId('user_id')->constrained()->cascadeOnDelete();
    });
}
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