SCOPE_IDENTITY在asp.net中不起作用？

Question

我试图通过一条记录一个接一个地执行两个查询来插入一条记录并获取其新生成的ID，但是不知道为什么它给了我以下错误。

Object cannot be cast from DBNull to other types

我的代码如下：（我不想使用sql存储过程）

SqlParameter sqlParam;
    int lastInsertedVideoId = 0;

    using (SqlConnection Conn = new SqlConnection(ObjUtils._ConnString))
    {
        Conn.Open();
        using (SqlCommand sqlCmd = Conn.CreateCommand())
        {
            string sqlInsertValues = "@Name,@Slug";
            string sqlColumnNames = "[Name],[Slug]";
            string sqlQuery = "INSERT INTO videos(" + sqlColumnNames + ") VALUES(" + sqlInsertValues + ");";
            sqlCmd.CommandText = sqlQuery;
            sqlCmd.CommandType = CommandType.Text;

            sqlParam = sqlCmd.Parameters.Add("@Name", SqlDbType.VarChar);
            sqlParam.Value = txtName.Text.Trim();

            sqlParam = sqlCmd.Parameters.Add("@Slug", SqlDbType.VarChar);
            sqlParam.Value = txtSlug.Text.Trim();


            sqlCmd.ExecuteNonQuery();

            //getting last inserted video id
            sqlCmd.CommandText = "SELECT SCOPE_IDENTITY() AS [lastInsertedVideoId]";
            using (SqlDataReader sqlDr = sqlCmd.ExecuteReader())
            {
                sqlDr.Read();
                lastInsertedVideoId = Convert.ToInt32(sqlDr["lastInsertedVideoId"]);
            }
        }
    }

    //tags insertion into tag table
    if (txtTags.Text.Trim().Length > 0 && lastInsertedVideoId > 0)
    {
        string sqlBulkTagInsert = "";
        string[] tags = txtTags.Text.Split(new string[] { "," }, StringSplitOptions.RemoveEmptyEntries);
        foreach (string tag in tags)
        {
            sqlBulkTagInsert += "INSERT INTO tags(VideoId, Tag) VALUES(" + lastInsertedVideoId + ", " + tag.Trim().ToLowerInvariant()+ "); ";
        }

        using (SqlConnection Conn = new SqlConnection(ObjUtils._ConnString))
        {
            Conn.Open();
            using (SqlCommand sqlCmd = Conn.CreateCommand())
            {
                string sqlQuery = sqlBulkTagInsert;
                sqlCmd.CommandText = sqlQuery;
                sqlCmd.CommandType = CommandType.Text;

                sqlCmd.ExecuteNonQuery();
            }
        }
    }

另外，如果可能，请检查上面的代码是否编码正确，或者我们可以对其进行更多优化以提高性能？

谢谢

Answer 1

对SCOPE_IDENTITY（）的调用不会被视为与您正在执行的INSERT命令位于同一“作用域”中。

本质上，您需要做的是更改行：

string sqlQuery = "INSERT INTO videos(" + sqlColumnNames + ") VALUES(" + sqlInsertValues + ");";

到：

string sqlQuery = "INSERT INTO videos(" + sqlColumnNames + ") VALUES(" + sqlInsertValues + "); SELECT SCOPE_IDENTITY() AS [lastInsertedVideoId]";

然后打电话

int lastVideoInsertedId = Convert.ToInt32(sqlCmd.ExecuteScalar());

而不是.ExecuteNonQuery和“ //获取最后插入的视频ID”注释后面的代码块。