无法在没有数据适配器的情况下启用约束

我有臭名昭著的"未能启用约束"异常，但这个问题的答案都不适用，因为我没有使用DataSet或TableAdatper：

DataTable tblTypes = connVeekun.ExecuteDataTable("SELECT id, damage_class_id, " +
    "(SELECT name FROM type_names WHERE type_names.type_id = types.id AND local_language_id = 1) AS name_ja, " +
    "(SELECT name FROM type_names WHERE type_names.type_id = types.id AND local_language_id = 9) AS name_en, " +
    "(SELECT name FROM type_names WHERE type_names.type_id = types.id AND local_language_id = 5) AS name_fr, " +
    "(SELECT name FROM type_names WHERE type_names.type_id = types.id AND local_language_id = 8) AS name_it, " +
    "(SELECT name FROM type_names WHERE type_names.type_id = types.id AND local_language_id = 6) AS name_de, " +
    "(SELECT name FROM type_names WHERE type_names.type_id = types.id AND local_language_id = 7) AS name_es, " +
    "(SELECT name FROM type_names WHERE type_names.type_id = types.id AND local_language_id = 3) AS name_ko " +
    "FROM types ORDER BY id");

帮助程序方法：

/// <summary>
/// Runs a command and returns a DataTable containing its results.
/// </summary>
/// <param name="db">Open data connection</param>
/// <param name="sqlstr">SQL string</param>
/// <param name="_params">List of parameters to use with the SQL</param>
public static DataTable ExecuteDataTable(this DbConnection conn, String sqlstr, params IDataParameter[] _params)
{
    DbCommand cmd = conn.CreateCommand();
    cmd.CommandText = sqlstr;
    cmd.Parameters.AddRange(_params);
    DbDataReader reader = cmd.ExecuteReader();
    DataTable result = new DataTable();
    result.Load(reader);
    return result;
}

失败的约束是name_ko列中存在 null 值。由于我没有使用DataAdapter，因此我无法更改（推断的）模式或禁用约束。在我的应用程序中，保留name_ko列的空度很重要，因此修改 SQL 以删除空值不是一种选择。

数据来自Eevee的Pokédex。