c# - SqlCommand.ExecuteScalar 避免空值

Question

关键是我有这段代码

var ojv = xmd.ExecuteScalar().ToString();
        if (ojv != null)
        {
            Console.WriteLine(ojv);
            var up = CreateQuery();
            up.CommandText = "UPDATE characters SET items=@items WHERE accId=@accId AND charId=@charId;";
            up.Parameters.AddWithValue("@items", ojv);
            up.Parameters.AddWithValue("@accId", acc.AccountId);
            up.Parameters.AddWithValue("@charId", charId);
            up.ExecuteNonQuery();
            var del = CreateQuery();
            del.CommandText = "DELETE FROM shop WHERE accId=@accId AND chrId=@chrId;";
            del.Parameters.AddWithValue("@accId", acc.AccountId);
            del.Parameters.AddWithValue("@chrId", charId);
            del.ExecuteNonQuery();
        }

但是，如果没有 ovj，它会返回 null，我需要避免这种情况，有什么办法可以让 ExecuteScalar 在找不到值时不返回 null？

Answer 1

只需在调用 ToString() 之前检查是否为 null。

    var result = xmd.ExecuteScalar();
        if (result != null)
        {
            var ojv = result.ToString();
            Console.WriteLine(ojv);
            var up = CreateQuery();
            up.CommandText = "UPDATE characters SET items=@items WHERE accId=@accId AND charId=@charId;";
            up.Parameters.AddWithValue("@items", ojv);
            up.Parameters.AddWithValue("@accId", acc.AccountId);
            up.Parameters.AddWithValue("@charId", charId);
            up.ExecuteNonQuery();
            var del = CreateQuery();
            del.CommandText = "DELETE FROM shop WHERE accId=@accId AND chrId=@chrId;";
            del.Parameters.AddWithValue("@accId", acc.AccountId);
            del.Parameters.AddWithValue("@chrId", charId);
            del.ExecuteNonQuery();
        }