How to: Execute a Query that Returns StructuralType Results
This topic shows how to execute a command against a conceptual model by using an EntityCommand object, and how to retrieve the StructuralType results by using an EntityDataReader. The EntityType, RowType and ComplexType classes derive from the StructuralType class.
To run the code in this example
Add the AdventureWorks Sales Model to your project and configure your project to use the Entity Framework. For more information, see How to: Use the Entity Data Model Wizard.
In the code page for your application, add the following
using
directives (Imports
in Visual Basic):using System; using System.Collections.Generic; using System.Data; using System.Data.Common; 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
Example
This example executes a query that returns EntityType results. If you pass the following query as an argument to the ExecuteStructuralTypeQuery
function, the function displays details about the Products
:
SELECT VALUE Product FROM AdventureWorksEntities.Products AS Product
If you pass a parameterized query, like the following, add the EntityParameter objects to the Parameters property on the EntityCommand object.
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