Cara: Menjalankan Kueri yang Mengembalikan Hasil StructuralType
Topik ini menunjukkan cara menjalankan perintah terhadap model konseptual dengan menggunakan objek EntityCommand, dan cara mengambil hasil StructuralType dengan menggunakan EntityDataReader. Kelas EntityType, RowType dan ComplexType berasal dari kelas StructuralType.
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 EntityType. Jika Anda meneruskan kueri berikut sebagai argumen ke fungsi ExecuteStructuralTypeQuery
, fungsi menampilkan detail tentang Products
:
SELECT VALUE Product FROM AdventureWorksEntities.Products AS Product
Jika Anda meneruskan kueri berparameter, seperti berikut ini, tambahkan objek EntityParameter ke properti Parameters pada objek EntityCommand.
SELECT VALUE product FROM AdventureWorksEntities.Products
AS product where product.ListPrice >= @price
static void ExecuteStructuralTypeQuery(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())
{
StructuralTypeVisitRecord(rdr as IExtendedDataRecord);
}
}
}
conn.Close();
}
}
static void StructuralTypeVisitRecord(IExtendedDataRecord record)
{
int fieldCount = record.DataRecordInfo.FieldMetadata.Count;
for (int fieldIndex = 0; fieldIndex < fieldCount; fieldIndex++)
{
Console.Write(record.GetName(fieldIndex) + ": ");
// 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;
// The EntityType, ComplexType and RowType are structural types
// that have members.
// Read only the PrimitiveType members of this structural type.
if (fieldTypeKind == BuiltInTypeKind.PrimitiveType)
{
// Primitive types are surfaced as plain objects.
Console.WriteLine(record.GetValue(fieldIndex).ToString());
}
}
}
}
Private Shared Sub ExecuteStructuralTypeQuery(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()
StructuralTypeVisitRecord(TryCast(rdr, IExtendedDataRecord))
End While
End Using
End Using
conn.Close()
End Using
End Sub
Private Shared Sub StructuralTypeVisitRecord(ByVal record As IExtendedDataRecord)
Dim fieldCount As Integer = record.DataRecordInfo.FieldMetadata.Count
For fieldIndex As Integer = 0 To fieldCount - 1
Console.Write(record.GetName(fieldIndex) & ": ")
' 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
' The EntityType, ComplexType and RowType are structural types
' that have members.
' Read only the PrimitiveType members of this structural type.
If fieldTypeKind = BuiltInTypeKind.PrimitiveType Then
' Primitive types are surfaced as plain objects.
Console.WriteLine(record.GetValue(fieldIndex).ToString())
End If
End If
Next
End Sub