如何:执行返回 PrimitiveType 结果的查询 (EntityClient)
本主题演示如何使用 EntityCommand 针对概念模型执行命令,以及如何使用 EntityDataReader 检索 PrimitiveType 结果。
运行本示例中的代码
将 AdventureWorks 销售模型添加到您的项目并将项目配置为使用实体框架 。 有关更多信息,请参见如何:使用实体数据模型向导(实体框架)。
在应用程序的代码页中,添加以下 using 语句(在 Visual Basic 中为 Imports):
Imports System Imports System.Collections.Generic Imports System.Collections Imports System.Data.Common Imports System.Data Imports System.IO Imports System.Data.SqlClient Imports System.Data.EntityClient Imports System.Data.Metadata.Edm
using System; using System.Collections.Generic; using System.Collections; using System.Data.Common; using System.Data; using System.IO; using System.Data.SqlClient; using System.Data.EntityClient; using System.Data.Metadata.Edm;
示例
本示例执行返回 PrimitiveType 结果的查询。 如果将以下查询作为参数传递给 ExecutePrimitiveTypeQuery
函数,则该函数将显示所有 Products 的平均定价:
SELECT VALUE AVG(p.ListPrice) FROM AdventureWorksEntities.Products as p
如果传递参数化查询(如下面的查询),请将 EntityParameter 对象添加到 EntityCommand 对象的 Parameters 属性。
CASE WHEN AVG({@score1,@score2,@score3}) < @total THEN TRUE ELSE FALSE END
Private Shared Sub ExecutePrimitiveTypeQuery(ByVal esqlQuery As String)
If esqlQuery.Length = 0 Then
Console.WriteLine("The query string is empty.")
Exit Sub
End If
Using conn As New EntityConnection("name=AdventureWorksEntities")
conn.Open()
' Create an EntityCommand.
Using cmd As EntityCommand = conn.CreateCommand()
cmd.CommandText = esqlQuery
' Execute the command.
Using rdr As EntityDataReader = cmd.ExecuteReader(CommandBehavior.SequentialAccess)
' Start reading results.
While rdr.Read()
Dim record As IExtendedDataRecord = TryCast(rdr, IExtendedDataRecord)
' For PrimitiveType
' the record contains exactly one field.
Dim fieldIndex As Integer = 0
Console.WriteLine("Value: " & record.GetValue(fieldIndex))
End While
End Using
End Using
conn.Close()
End Using
End Sub
static void ExecutePrimitiveTypeQuery(string esqlQuery)
{
if (esqlQuery.Length == 0)
{
Console.WriteLine("The query string is empty.");
return;
}
using (EntityConnection conn =
new EntityConnection("name=AdventureWorksEntities"))
{
conn.Open();
// Create an EntityCommand.
using (EntityCommand cmd = conn.CreateCommand())
{
cmd.CommandText = esqlQuery;
// Execute the command.
using (EntityDataReader rdr =
cmd.ExecuteReader(CommandBehavior.SequentialAccess))
{
// Start reading results.
while (rdr.Read())
{
IExtendedDataRecord record = rdr as IExtendedDataRecord;
// For PrimitiveType
// the record contains exactly one field.
int fieldIndex = 0;
Console.WriteLine("Value: " + record.GetValue(fieldIndex));
}
}
}
conn.Close();
}
}