Cara: Menjalankan Kueri yang Mengembalikan Hasil RefType
Topik ini menunjukkan cara menjalankan perintah terhadap model konseptual dengan menggunakan objek EntityCommand, dan cara mengambil hasil RefType dengan menggunakan EntityDataReader.
Untuk menjalankan kode dalam contoh ini
Tambahkan AdventureWorks Sales Model ke proyek Anda dan konfigurasikan proyek Anda untuk menggunakan Entity Framework. Untuk informasi selengkapnya, lihat Cara: Menggunakan Wizard Model Data Entitas.
Di halaman kode untuk aplikasi Anda, tambahkan pernyataan
using
berikut (Imports
dalam Visual Basic):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;
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
Contoh
Contoh ini menjalankan kueri yang mengembalikan hasil RefType. Jika Anda meneruskan kueri berikut sebagai argumen ke fungsi ExecuteRefTypeQuery
, fungsi mengembalikan referensi ke entitas:
SELECT REF(p) FROM AdventureWorksEntities.Products as p
Jika Anda meneruskan kueri berparameter, seperti berikut ini, tambahkan objek EntityParameter ke properti Parameters pada objek EntityCommand.
SELECT REF(p) FROM AdventureWorksEntities.Products as p WHERE p.ProductID == @productID
static public void ExecuteRefTypeQuery(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())
{
RefTypeVisitRecord(rdr as IExtendedDataRecord);
}
}
}
conn.Close();
}
}
static void RefTypeVisitRecord(IExtendedDataRecord record)
{
// For RefType the record contains exactly one field.
int fieldIndex = 0;
// If the field is flagged as DbNull, the shape of the value is undetermined.
// An attempt to get such a value may trigger an exception.
if (record.IsDBNull(fieldIndex) == false)
{
BuiltInTypeKind fieldTypeKind = record.DataRecordInfo.FieldMetadata[fieldIndex].
FieldType.TypeUsage.EdmType.BuiltInTypeKind;
//read only fields that contain PrimitiveType
if (fieldTypeKind == BuiltInTypeKind.RefType)
{
// Ref types are surfaced as EntityKey instances.
// The containing record sees them as atomic.
EntityKey key = record.GetValue(fieldIndex) as EntityKey;
// Get the EntitySet name.
Console.WriteLine("EntitySetName " + key.EntitySetName);
// Get the Name and the Value information of the EntityKey.
foreach (EntityKeyMember keyMember in key.EntityKeyValues)
{
Console.WriteLine(" Key Name: " + keyMember.Key);
Console.WriteLine(" Key Value: " + keyMember.Value);
}
}
}
}
Private Shared Sub ExecuteRefTypeQuery(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()
RefTypeVisitRecord(TryCast(rdr, IExtendedDataRecord))
End While
End Using
End Using
conn.Close()
End Using
End Sub
Private Shared Sub RefTypeVisitRecord(ByVal record As IExtendedDataRecord)
' For RefType the record contains exactly one field.
Dim fieldIndex As Integer = 0
' If the field is flagged as DbNull, the shape of the value is undetermined.
' An attempt to get such a value may trigger an exception.
If record.IsDBNull(fieldIndex) = False Then
Dim fieldTypeKind As BuiltInTypeKind = record.DataRecordInfo.FieldMetadata(fieldIndex).FieldType.TypeUsage.EdmType.BuiltInTypeKind
'read only fields that contain PrimitiveType
If fieldTypeKind = BuiltInTypeKind.RefType Then
' Ref types are surfaced as EntityKey instances.
' The containing record sees them as atomic.
Dim key As EntityKey = TryCast(record.GetValue(fieldIndex), EntityKey)
' Get the EntitySet name.
Console.WriteLine("EntitySetName " & key.EntitySetName)
' Get the Name and the Value information of the EntityKey.
For Each keyMember As EntityKeyMember In key.EntityKeyValues
Console.WriteLine(" Key Name: " & keyMember.Key)
Console.WriteLine(" Key Value: " & keyMember.Value)
Next
End If
End If
End Sub