How to: Execute a Query that Returns RefType Results (EntityClient)

This topic provides an example of how to execute a command against an Entity Data Model by using EntityCommand, and how to retrieve the RefType results by using EntityDataReader.

To run the code in this example

1. Add the AdventureWorks Sales Model to your project and configure your project to use the Entity Framework. To do this, do one of the following:

   • If you have the Entity Dada Model tools installed, complete the procedure in How to: Use the Entity Data Model Wizard (Entity Framework).

   • Otherwise, complete the procedures in How to: Manually Configure an Entity Framework Project and How to: Manually Define an Entity Data Model (Entity Framework).

2. In the code page for your application, add the following using statements (Imports in Visual Basic):.

   Imports System
   Imports System.Collections.Generic
   Imports System.Collections
   Imports System.Data.Common
   Imports System.Data
   Imports System.Data.SqlClient
   Imports System.Data.EntityClient
   Imports System.Data.Metadata.Edm
   Imports System.IO
   ' Add AdventureWorksModel prepended with the root namespace for the project.
   'Imports ProjectName.AdventureWorksModel
   

   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 AdventureWorksModel;
   using System.Data.Metadata.Edm;
   

Example

To test the code, pass the following query as an argument to the ExectueRefTypeQuery function:

"SELECT REF(p) FROM AdventureWorksEntities.Product as p"

The query above returns the RefType results.

Sub ExectueRefTypeQuery(ByVal esqlQuery As String)
    If (esqlQuery.Length = 0) Then
        Console.WriteLine("The query string is empty.")
        Return
    End If

    Using conn As EntityConnection = New EntityConnection("name=AdventureWorksEntities")
        conn.Open()

        Try
            ' Create an EntityCommand.
            Using cmd As EntityCommand = conn.CreateCommand()
                cmd.CommandText = esqlQuery
                ' Execute the command.
                Using reader As EntityDataReader = cmd.ExecuteReader(CommandBehavior.SequentialAccess)
                    Do While (reader.Read())
                        RefTypeVisitRecord(CType(reader, IExtendedDataRecord))
                    Loop
                End Using
            End Using
        Catch ex As Exception
            Console.WriteLine(ex.ToString())
        End Try
        conn.Close()
    End Using
End Sub

Sub RefTypeVisitRecord(ByVal record As IExtendedDataRecord)
    ' For RefType the record contains exactly one field.
    Dim fieldIndex As Integer
    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) 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 = CType(record.GetValue(fieldIndex), EntityKey)
            ' Get the EntitySet name.
            Console.WriteLine("EntitySetName " + key.EntitySetName)
            ' Get the Name and the Value information of the EntityKey.
            Dim keyMember As EntityKeyMember
            For Each keyMember In key.EntityKeyValues
                Console.WriteLine("   Key Name: " + keyMember.Key)
                Console.WriteLine("   Key Value: " + keyMember.Value)
            Next
        End If
    End If
End Sub

static void ExectueRefTypeQuery(string esqlQuery)
{
    if (esqlQuery.Length == 0)
    {
        Console.WriteLine("The query string is empty.");
        return;
    }

    using (EntityConnection conn =
        new EntityConnection("name=AdventureWorksEntities"))
    {
        conn.Open();

        try
        {
            // 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);
                    }
                }
            }
        }
        catch (EntityException ex)
        {
            Console.WriteLine(ex.ToString());
        }
        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);
            }
        }
    }
}

See Also

Concepts

Entity SQL Reference

Other Resources

Working with EntityClient (Entity Framework Tasks)