从数据读取器填充数据表


103

我在C#(MS VS2008)中做一个基本的事情,除了特定的代码外,还有更多关于适当设计的问题。

我正在创建一个数据表,然后尝试从一个数据读取器(基于SQL存储过程)加载该数据表。我想知道的是,加载数据表的最有效方法是执行while语句,还是有更好的方法。

对我来说,唯一的缺点是我必须手动输入要在while语句中添加的字段,但是我也不知道如何自动执行该操作,因为我不想从SP中选择所有字段,但是在我看来这并不是什么大问题。

尽管我对代码本身并不满意,甚至对我所问的内容并不满意,但我还是将代码片段包括在我所做的全部工作之下。此外,我想知道自己的方法是什么,如果我的策略错误/效率低下,我将在稍后寻求代码帮助。

var dtWriteoffUpload = new DataTable();
dtWriteoffUpload.Columns.Add("Unit");
dtWriteoffUpload.Columns.Add("Year");
dtWriteoffUpload.Columns.Add("Period");
dtWriteoffUpload.Columns.Add("Acct");
dtWriteoffUpload.Columns.Add("Descr");
dtWriteoffUpload.Columns.Add("DEFERRAL_TYPE");
dtWriteoffUpload.Columns.Add("NDC_Indicator");
dtWriteoffUpload.Columns.Add("Mgmt Cd");
dtWriteoffUpload.Columns.Add("Prod");
dtWriteoffUpload.Columns.Add("Node");
dtWriteoffUpload.Columns.Add("Curve_Family");
dtWriteoffUpload.Columns.Add("Sum Amount");
dtWriteoffUpload.Columns.Add("Base Curr");
dtWriteoffUpload.Columns.Add("Ledger");  

cmd = util.SqlConn.CreateCommand();
cmd.CommandTimeout = 1000;
cmd.CommandType = CommandType.StoredProcedure;
cmd.CommandText = "proc_writeoff_data_details";
cmd.Parameters.Add("@whoAmI", SqlDbType.VarChar).Value = 

WindowsIdentity.GetCurrent().Name;

cmd.Parameters.Add("@parmEndDateKey", SqlDbType.VarChar).Value = myMostRecentActualDate;
cmd.Parameters.Add("@countrykeys", SqlDbType.VarChar).Value = myCountryKey;
cmd.Parameters.Add("@nodekeys", SqlDbType.VarChar).Value = "1,2";
break;


dr = cmd.ExecuteReader();
while (dr.Read())                    
{
    dtWriteoffUpload.Rows.Add(dr["country name"].ToString(), dr["country key"].ToString());
}

Answers:


283

您可以DataTable使用Load()接受的方法直接从数据读取器加载IDataReader

var dataReader = cmd.ExecuteReader();
var dataTable = new DataTable();
dataTable.Load(dataReader);

2
您保存了我的一天(Y)
Uzair Xlade

1
这是我花了一个星期寻找的东西!
TheTechy

17

请检查以下代码。自动将其转换为DataTable

private void ConvertDataReaderToTableManually()
    {
        SqlConnection conn = null;
        try
        {
            string connString = ConfigurationManager.ConnectionStrings["NorthwindConn"].ConnectionString;
            conn = new SqlConnection(connString);
            string query = "SELECT * FROM Customers";
            SqlCommand cmd = new SqlCommand(query, conn);
            conn.Open();
            SqlDataReader dr = cmd.ExecuteReader(CommandBehavior.CloseConnection);
            DataTable dtSchema = dr.GetSchemaTable();
            DataTable dt = new DataTable();
            // You can also use an ArrayList instead of List<>
            List<DataColumn> listCols = new List<DataColumn>();

            if (dtSchema != null)
            {
                foreach (DataRow drow in dtSchema.Rows)
                {
                    string columnName = System.Convert.ToString(drow["ColumnName"]);
                    DataColumn column = new DataColumn(columnName, (Type)(drow["DataType"]));
                    column.Unique = (bool)drow["IsUnique"];
                    column.AllowDBNull = (bool)drow["AllowDBNull"];
                    column.AutoIncrement = (bool)drow["IsAutoIncrement"];
                    listCols.Add(column);
                    dt.Columns.Add(column);
                }
            }

            // Read rows from DataReader and populate the DataTable
            while (dr.Read())
            {
                DataRow dataRow = dt.NewRow();
                for (int i = 0; i < listCols.Count; i++)
                {
                    dataRow[((DataColumn)listCols[i])] = dr[i];
                }
                dt.Rows.Add(dataRow);
            }
            GridView2.DataSource = dt;
            GridView2.DataBind();
        }
        catch (SqlException ex)
        {
            // handle error
        }
        catch (Exception ex)
        {
            // handle error
        }
        finally
        {
            conn.Close();
        }

    }

有一个直接的选项可以将datareader加载到datatable,那么为什么有人会使用它呢?
阿巴斯2015年

@sarathkumar干得好..我一直在寻找这样的代码
SimpleGuy 2015年

@Abbas Coz,内置数据加载非常慢
SimpleGuy 2015年

dt.Load(reader)也不总是有效-我Object reference not set to an instance of an object可能会收到那些讨厌的错误,可能是当我没有返回任何行时。这样的手册会派上用场。我试了一下,不得不摆脱那些column.在行dtSchema foreach,因为它说,这是一个非法铸造循环bool(bool)drow["IsUnique"]。我不需要它们,获取列名称以填充新名称DataTable就足够了。这样可以帮助我ds.Fill(adapter)解决无法使用加载大表的问题SELECT * FROM MyTable
vapcguy

一个警告-如果任何列中都有空值,则必须处理它们,否则此函数将导致异常。必须检查if (!dr.IsDBNull(i))for循环中的下一件事。然后,您要做您的工作dataRow。但是,这时您需要一个elseon,以防您找到null。如果你这样做,你要搞清楚你要添加的列的类型,并相应地分配空(即你可以指定String.Empty,如果它的类型的System.String,但你必须分配0,如果它的System.Int16(布尔字段)或System.Decimal
vapcguy

13

如果您要加载DataTable,请利用SqlDataAdapter代替:

DataTable dt = new DataTable();

using (SqlConnection c = new SqlConnection(cString))
using (SqlDataAdapter sda = new SqlDataAdapter(sql, c))
{
    sda.SelectCommand.CommandType = CommandType.StoredProcedure;
    sda.SelectCommand.Parameters.AddWithValue("@parm1", val1);
    ...

    sda.Fill(dt);
}

您甚至不需要定义列。只需创建DataTableFill

cString是您的连接字符串,sql是存储过程命令。


1
这里唯一的问题是,如果您发现列/值在填充过程中导致异常,则它不会提供任何详细信息,例如您可以使用a SqlDataReader并通过遍历字段读取它们。
vapcguy

9

正如Sagi在回答中所说的,DataTable.Load是一个很好的解决方案。如果尝试从单个读取器加载多个表,则无需调用DataReader.NextResult。DataTable.Load方法还将阅读器前进到下一个结果集(如果有)。

// Read every result set in the data reader.
while (!reader.IsClosed)
{
    DataTable dt = new DataTable();
    // DataTable.Load automatically advances the reader to the next result set
    dt.Load(reader);
    items.Add(dt);
}

5

我也对此进行了研究,在将SqlDataAdapter.Fill方法与SqlDataReader.Load函数进行比较之后,我发现SqlDataAdapter.Fill方法的速度是我一直使用的结果集的两倍以上。

使用的代码:

    [TestMethod]
    public void SQLCommandVsAddaptor()
    {
        long AdapterFillLargeTableTime, readerLoadLargeTableTime, AdapterFillMediumTableTime, readerLoadMediumTableTime, AdapterFillSmallTableTime, readerLoadSmallTableTime, AdapterFillTinyTableTime, readerLoadTinyTableTime;

        string LargeTableToFill = "select top 10000 * from FooBar";
        string MediumTableToFill = "select top 1000 * from FooBar";
        string SmallTableToFill = "select top 100 * from FooBar";
        string TinyTableToFill = "select top 10 * from FooBar";

        using (SqlConnection sconn = new SqlConnection("Data Source=.;initial catalog=Foo;persist security info=True; user id=bar;password=foobar;"))
        {
            // large data set measurements
            AdapterFillLargeTableTime = MeasureExecutionTimeMethod(sconn, LargeTableToFill, ExecuteDataAdapterFillStep);
            readerLoadLargeTableTime = MeasureExecutionTimeMethod(sconn, LargeTableToFill, ExecuteSqlReaderLoadStep);
            // medium data set measurements
            AdapterFillMediumTableTime = MeasureExecutionTimeMethod(sconn, MediumTableToFill, ExecuteDataAdapterFillStep);
            readerLoadMediumTableTime = MeasureExecutionTimeMethod(sconn, MediumTableToFill, ExecuteSqlReaderLoadStep);
            // small data set measurements
            AdapterFillSmallTableTime = MeasureExecutionTimeMethod(sconn, SmallTableToFill, ExecuteDataAdapterFillStep);
            readerLoadSmallTableTime = MeasureExecutionTimeMethod(sconn, SmallTableToFill, ExecuteSqlReaderLoadStep);
            // tiny data set measurements
            AdapterFillTinyTableTime = MeasureExecutionTimeMethod(sconn, TinyTableToFill, ExecuteDataAdapterFillStep);
            readerLoadTinyTableTime = MeasureExecutionTimeMethod(sconn, TinyTableToFill, ExecuteSqlReaderLoadStep);
        }
        using (StreamWriter writer = new StreamWriter("result_sql_compare.txt"))
        {
            writer.WriteLine("10000 rows");
            writer.WriteLine("Sql Data Adapter 100 times table fill speed 10000 rows: {0} milliseconds", AdapterFillLargeTableTime);
            writer.WriteLine("Sql Data Reader 100 times table load speed 10000 rows: {0} milliseconds", readerLoadLargeTableTime);
            writer.WriteLine("1000 rows");
            writer.WriteLine("Sql Data Adapter 100 times table fill speed 1000 rows: {0} milliseconds", AdapterFillMediumTableTime);
            writer.WriteLine("Sql Data Reader 100 times table load speed 1000 rows: {0} milliseconds", readerLoadMediumTableTime);
            writer.WriteLine("100 rows");
            writer.WriteLine("Sql Data Adapter 100 times table fill speed 100 rows: {0} milliseconds", AdapterFillSmallTableTime);
            writer.WriteLine("Sql Data Reader 100 times table load speed 100 rows: {0} milliseconds", readerLoadSmallTableTime);
            writer.WriteLine("10 rows");
            writer.WriteLine("Sql Data Adapter 100 times table fill speed 10 rows: {0} milliseconds", AdapterFillTinyTableTime);
            writer.WriteLine("Sql Data Reader 100 times table load speed 10 rows: {0} milliseconds", readerLoadTinyTableTime);

        }
        Process.Start("result_sql_compare.txt");
    }

    private long MeasureExecutionTimeMethod(SqlConnection conn, string query, Action<SqlConnection, string> Method)
    {
        long time; // know C#
        // execute single read step outside measurement time, to warm up cache or whatever
        Method(conn, query);
        // start timing
        time = Environment.TickCount;
        for (int i = 0; i < 100; i++)
        {
            Method(conn, query);
        }
        // return time in milliseconds
        return Environment.TickCount - time;
    }

    private void ExecuteDataAdapterFillStep(SqlConnection conn, string query)
    {
        DataTable tab = new DataTable();
        conn.Open();
        using (SqlDataAdapter comm = new SqlDataAdapter(query, conn))
        {
            // Adapter fill table function
            comm.Fill(tab);
        }
        conn.Close();
    }

    private void ExecuteSqlReaderLoadStep(SqlConnection conn, string query)
    {
        DataTable tab = new DataTable();
        conn.Open();
        using (SqlCommand comm = new SqlCommand(query, conn))
        {
            using (SqlDataReader reader = comm.ExecuteReader())
            {
                // IDataReader Load function
                tab.Load(reader);
            }
        }
        conn.Close();
    }

结果:

10000 rows:
Sql Data Adapter 100 times table fill speed 10000 rows: 11782 milliseconds
Sql Data Reader  100 times table load speed 10000 rows: 26047 milliseconds
1000 rows:
Sql Data Adapter 100 times table fill speed 1000 rows: 984  milliseconds
Sql Data Reader  100 times table load speed 1000 rows: 2031 milliseconds
100 rows:
Sql Data Adapter 100 times table fill speed 100 rows: 125 milliseconds
Sql Data Reader  100 times table load speed 100 rows: 235 milliseconds
10 rows:
Sql Data Adapter 100 times table fill speed 10 rows: 32 milliseconds
Sql Data Reader  100 times table load speed 10 rows: 93 milliseconds

对于性能问题,使用SqlDataAdapter.Fill方法效率更高。因此,除非您想用脚射击自己,否则请使用它。它适用于小型和大型数据集。

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