DbDataReader、NextResult() 和填充多个表

Posted 2023-03-12

【中文标题】DbDataReader、NextResult() 和填充多个表

【英文标题】：DbDataReader, NextResult() and filling more than one table

【发布时间】：2012-07-06 22:46:35

【问题描述】：

这个问题是我previous 的一个问题的延续。在不涉及太多细节的情况下，我将使用 2 个相关的一对多表填充数据集。 所以，我现在的问题是 - 为什么这段代码运行良好

public DataAgencyR_DataSet SelectOne(int id)

    DataAgencyR_DataSet result = new DataAgencyR_DataSet();
    using (DbCommand command = Connection.CreateCommand())
    
        try
                       
            command.CommandText = SqlStrings.SelectDataAgencyR_SelectOne();

            var param = ParametersBuilder.CreateByKey(command, "ID_DeclAgenc", id, "ID_DeclAgenc");
            command.Parameters.Add(param);
            Connection.Open();
            using (DbDataReader reader = command.ExecuteReader())
            
                while (reader.Read())
                
                    System.Diagnostics.Trace.WriteLine(String.Format("0-1", reader[0], reader[1]));
                
                System.Diagnostics.Trace.WriteLine("-------------");
                reader.NextResult();
                while (reader.Read())
                
                    System.Diagnostics.Trace.WriteLine(String.Format("0-1", reader[0], reader[1]));
                
            

        
        catch (DbException e)
        
            Logger.Error(e.Message, e);
            throw new DataAccessException("Error occurs while SelectOne method porcessed", e);
        
        finally
        
            if (Connection.State != ConnectionState.Closed)                     Connection.Close();
        
    
    return result;


public static string SelectDataAgencyR_SelectOne()

    return "SELECT a.* FROM t0_DataAgency_R a WHERE a.SetToPartners = 1 AND a.ID_DeclAgenc = @ID_DeclAgenc;" +
                   "SELECT c.* FROM t01_ChoiceParam_R c JOIN t0_DataAgency_R a on a.ID_DeclAgenc = c.ID_DeclAgenc WHERE SetToPartners = 1 AND a.ID_DeclAgenc = @ID_DeclAgenc";

这不是

public DataAgencyR_DataSet SelectOne(int id)

    DataAgencyR_DataSet result = new DataAgencyR_DataSet();

    using (DbCommand command = Connection.CreateCommand())
    
        try
                       
            command.CommandText = SqlStrings.SelectDataAgencyR_SelectOne();             
            var param = ParametersBuilder.CreateByKey(command, "ID_DeclAgenc", id, "ID_DeclAgenc");
            command.Parameters.Add(param);
            Connection.Open();
            using (DbDataReader reader = command.ExecuteReader())
            
                result.t0_DataAgency_R.Load(reader);
                reader.NextResult();
                result.t01_ChoiceParam_R.Load(reader);
            
        
        catch (DbException e)
        
            Logger.Error(e.Message, e);
            throw new DataAccessException("Error occurs while SelectOne method porcessed", e);
        
        finally
        
            if (Connection.State != ConnectionState.Closed) Connection.Close();
        
    
    return result;



public static string SelectDataAgencyR_SelectOne()

    return "SELECT a.* FROM t0_DataAgency_R a WHERE a.SetToPartners = 1 AND a.ID_DeclAgenc = @ID_DeclAgenc;" +
                   "SELECT c.* FROM t01_ChoiceParam_R c JOIN t0_DataAgency_R a on a.ID_DeclAgenc = c.ID_DeclAgenc WHERE SetToPartners = 1 AND a.ID_DeclAgenc = @ID_DeclAgenc";

在第二个示例之后，我只填写了 result.t0_DataAgency_R 表 - 但没有填写 result.t01_ChoiceParam_R。为什么会这样？

提前致谢

【参考方案1】：

DataTable.Load 自动将阅读器推进到下一个结果。因此，您应该删除对NextResult 的显式调用。

意思：

using (DbDataReader reader = command.ExecuteReader())

    result.t0_DataAgency_R.Load(reader);
    result.t01_ChoiceParam_R.Load(reader);

【讨论】：

如果结果集数量不定怎么办？如何检查何时停止检查下一个结果？

【参考方案2】：

添加数据集...我们曾经使用 SqlDataAdapter 并返回一个数据集，但没有利用任何离线功能等，因此 SqlDataReader 更适合。这是填充数据集的代码。发现这总体上快了大约 10%。

                Dim s As DataSet = New DataSet()

                Using reader As SqlDataReader = command.ExecuteReader()
                    Dim tables As New List(Of DataTable)
                    Do
                        Dim table As New DataTable()
                        table.Load(reader)
                        tables.Add(table)
                        s.Tables.Add(table)
                    Loop While Not reader.IsClosed

                    s.Load(reader, LoadOption.OverwriteChanges, tables.ToArray())
                End Using