Procedura: associare oggetti a controlli Windows Form (Entity Framework)

Object Services consente di associare controlli Windows Form, come ComboBox o DataGridView a un oggetto EntityCollection o a un risultato di ObjectQuery. È consigliabile non associare i controlli direttamente a un oggetto ObjectQuery. Associare invece i controlli al risultato del metodo Execute. Per ulteriori informazioni, vedere Associazione di oggetti ai controlli (Entity Framework).

L'esempio incluso in questo argomento è basato sul modello Sales di AdventureWorks. Per eseguire il codice incluso in questo esempio, è necessario avere già aggiunto il modello Sales di AdventureWorks al progetto e avere configurato il progetto per l'utilizzo di Entity Framework. A tale scopo, completare le procedure descritte in Procedura: configurare manualmente un progetto di Entity Framework e Procedura: definire manualmente un modello EDM (Entity Framework).

Esempio

L'esempio seguente deriva da un Windows Form. Quando il form viene caricato, viene restituita una classe ObjectResult di oggetti SalesOrderHeader chiamando il metodo Execute di ObjectQuery. Questo risultato è associato a una casella combinata. Quando viene selezionato un ordine, la classe EntityCollection correlata di oggetti SalesOrderDetail viene associata a un controllo DataGridView.

Imports System
Imports System.Collections.Generic
Imports System.Collections
Imports System.ComponentModel
Imports System.Data
Imports System.Drawing
Imports System.Linq
Imports System.Text
Imports System.Windows.Forms
Imports System.Data.Objects
Imports System.Data.Objects.DataClasses
Imports AdventureWorksModel

Public Class Main
    Public Sub New()
        ' Initializes the designer-generated controls.
        InitializeComponent()
    End Sub
    Private context As AdventureWorksEntities
    Private customerId As Integer = 277
    Private Sub Main_Load(ByVal sender As System.Object, _
                           ByVal e As System.EventArgs) _
                           Handles MyBase.Load
        ' Initialize the object context.
        context = New AdventureWorksEntities()
        Try
            ' Create a query for orders that includes line items.
            Dim orderQuery As ObjectQuery(Of SalesOrderHeader) = _
            context.SalesOrderHeader _
                    .Where("it.CustomerID = @customerId", _
                    New ObjectParameter("customerId", customerId)) _
            .Include("SalesOrderDetail")

            ' Bind the combo box to the ObjectResult of SalesOrderHeader 
            ' that is returned when the query is executed.
            Me.ordersListBox.DataSource = orderQuery.Execute(MergeOption.AppendOnly)

            ' Display the PO number in the combo box.
            Me.ordersListBox.DisplayMember = "PurchaseOrderNumber"

        Catch ex As EntitySqlException
            MessageBox.Show(ex.Message)
        End Try
    End Sub
    Private Sub ordersListBox_SelectedIndexChanged(ByVal sender As System.Object, _
                                                    ByVal e As System.EventArgs) _
                                                    Handles ordersListBox.SelectedIndexChanged
        ' Get the currently selected SalesOrderHeader object.
        Dim order As SalesOrderHeader = CType(Me.ordersListBox.SelectedItem,  _
        SalesOrderHeader)

        ' Bind the items for this order to the DataGridView.
        lineItemsDataGrid.DataSource = order.SalesOrderDetail
    End Sub

    Private Sub saveButton_Click(ByVal sender As System.Object, _
                                  ByVal e As System.EventArgs) _
                                  Handles saveButton.Click
        ' Get the current order. 
        Dim order As SalesOrderHeader = CType(ordersListBox.SelectedItem,  _
            SalesOrderHeader)

        Try
            ' Save changes in the object context.
            context.SaveChanges(True)

        Catch ex As OptimisticConcurrencyException
            ' Resolve the concurrently conflict by refreshing the 
            ' object context before saving changes. 
            context.Refresh(RefreshMode.ClientWins, order.SalesOrderDetail)

            ' Resave changes in the object context.
            context.SaveChanges(True)
        Catch ex As Exception
            MessageBox.Show(ex.InnerException.Message, "An error has occured")
        Finally
            ' Refresh the latest data from the database.
            context.Refresh(RefreshMode.StoreWins, order)
            Me.Refresh()
        End Try
    End Sub
End Class

using System;
using System.Collections.Generic;
using System.Collections;
using System.ComponentModel;
using System.Data;
using System.Drawing;
using System.Linq;
using System.Text;
using System.Windows.Forms;
using System.Data.Objects;
using System.Data.Objects.DataClasses;
using AdventureWorksModel;

namespace Microsoft.Samples.Edm
{
    public partial class Main : Form
    {
        private AdventureWorksEntities context;
        private int customerId = 277;

        public Main()
        {
            // Initializes the designer-generated controls.
            InitializeComponent();
        }
        
        private void Main_Load(object sender, EventArgs e)
        {
            // Initialize the object context.
            context = new AdventureWorksEntities();
            try
            {
                // Create a query for orders that includes line items.
                ObjectQuery<SalesOrderHeader> orderQuery = context.SalesOrderHeader
                    .Where("it.CustomerID = @customerId", 
                    new ObjectParameter("customerId", customerId))
                    .Include("SalesOrderDetail");

                // Bind the combo box to the ObjectResult of SalesOrderHeader 
                // that is returned when the query is executed.
                this.ordersListBox.DataSource = orderQuery.Execute(MergeOption.AppendOnly);

                // Display the PO number in the combo box.
                this.ordersListBox.DisplayMember = "PurchaseOrderNumber";
            }
            catch (EntitySqlException ex)
            {
                MessageBox.Show(ex.Message);
            }
        }

        private void ordersListBox_SelectedIndexChanged(object sender, EventArgs e)
        {
            // Get the currently selected SalesOrderHeader object.
            SalesOrderHeader order = (SalesOrderHeader)this.ordersListBox.SelectedItem;

            // Bind the items for this order to the DataGridView.
            lineItemsDataGrid.DataSource = order.SalesOrderDetail;
        }

        private void saveButton_Click(object sender, EventArgs e)
        {
            // Get the current order.    
            SalesOrderHeader order = (SalesOrderHeader)ordersListBox.SelectedItem;

            try
            {
                // Save changes in the object context.
                context.SaveChanges(true);
            }
            catch (OptimisticConcurrencyException)
            {
                // Resolve the concurrently conflict by refreshing the 
                // object context before saving changes. 
                context.Refresh(RefreshMode.ClientWins, order.SalesOrderDetail);

                // Resave changes in the object context.
                context.SaveChanges(true);
            }
            catch (Exception ex)
            {
                MessageBox.Show(ex.InnerException.Message, "An error has occured");
            }
            finally
            {
                //  Refresh the latest data from the database.
                context.Refresh(RefreshMode.StoreWins, order);
                this.Refresh();
            }
        }
    }
}

Vedere anche

Attività

Procedura: associare oggetti a controlli Windows Presentation Foundation (Entity Framework)
Procedura: aggiungere un oggetto come origine dati progetto (Entity Framework)

Concetti

Associazione di oggetti ai controlli (Entity Framework)
Associare dati di entità a controlli (Scenari dell'applicazione)