Procédure : exécuter une requête qui retourne une collection de types primitifs (Entity Framework)
Cette rubrique fournit des exemples d'exécution de requêtes qui retournent une collection de types primitifs. Pour retourner un seul objet, utilisez l'une des méthodes suivantes sur votre requête : First, FirstOrDefault, Single, SingleOrDefault.
Le même exemple est repris en utilisant chacune des technologies de requête Entity Framework suivantes :
LINQ to Entities
Entity SQL avec ObjectQuery<T>
Méthodes du Générateur de requêtes d'ObjectQuery<T>
L'exemple de cette rubrique est basé sur le modèle de vente Adventure Works Sales Model. Pour exécuter le code de cette rubrique, vous devez déjà avoir ajouté le modèle de vente AdventureWorks à votre projet et configuré ce dernier pour qu'il utilise Entity Framework. Pour plus d'informations, consultez Procédure : utiliser l'Assistant EDM (Entity Framework) ou Procédure : configurer manuellement un projet Entity Framework et Procédure : définir manuellement un modèle EDM (Entity Data Model) (Entity Framework).
Exemple
L'exemple ci-dessous utilise LINQ to Entities .
Dim contactId As Integer = 377
Using context As New AdventureWorksEntities()
' Select a value.
Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders
Dim orderQuery As IQueryable(Of Int32) = From order In orders _
Where order.Contact.ContactID = contactId _
Select order.PurchaseOrderNumber.Length
' Iterate through the collection of values.
For Each result As Int32 In orderQuery
Console.WriteLine("{0}", result)
Next
' Use a nullable DateTime value because ShipDate can be null.
Dim shipDateQuery As IQueryable(Of System.Nullable(Of DateTime)) = From order In orders _
Where order.Contact.ContactID = contactId _
Select order.ShipDate
' Iterate through the collection of values.
For Each shipDate As System.Nullable(Of DateTime) In shipDateQuery
Dim shipDateMessage As String = "date not set"
If shipDate IsNot Nothing Then
shipDateMessage = shipDate.ToString()
End If
Console.WriteLine("Ship Date: {0}.", shipDateMessage)
Next
End Using
int contactId = 377;
using (AdventureWorksEntities context
= new AdventureWorksEntities())
{
// Select a value.
ObjectSet<SalesOrderHeader> orders
= context.SalesOrderHeaders;
IQueryable<Int32> orderQuery =
from order in orders
where order.Contact.ContactID == contactId
select order.PurchaseOrderNumber.Length;
// Iterate through the collection of values.
foreach (Int32 result in orderQuery)
{
Console.WriteLine("{0}", result);
}
// Use a nullable DateTime value because ShipDate can be null.
IQueryable<DateTime?> shipDateQuery =
from order in orders
where order.Contact.ContactID == contactId
select order.ShipDate;
// Iterate through the collection of values.
foreach (DateTime? shipDate in shipDateQuery)
{
string shipDateMessage = "date not set";
if (shipDate != null)
{
shipDateMessage = shipDate.ToString();
}
Console.WriteLine("Ship Date: {0}.", shipDateMessage);
}
}
L'exemple ci-dessous utilise Entity SQL .
Dim contactId As Integer = 377
Using context As New AdventureWorksEntities()
Dim orderQueryString As String = "SELECT VALUE Length(order.PurchaseOrderNumber) FROM " & _
" AdventureWorksEntities.SalesOrderHeaders AS order WHERE order.CustomerID = @contactId"
Dim shipDateQueryString As String = "SELECT VALUE order.ShipDate" & _
" FROM AdventureWorksEntities.SalesOrderHeaders AS order WHERE order.CustomerID = @contactId"
' Use the SelectValue method to select a value.
Dim orderQuery As New ObjectQuery(Of Int32)(orderQueryString, context, MergeOption.NoTracking)
orderQuery.Parameters.Add(New ObjectParameter("contactId", contactId))
' Iterate through the collection of values.
For Each result As Int32 In orderQuery
Console.WriteLine("{0}", result)
Next
' Use a nullable DateTime value because ShipDate can be null.
Dim shipDateQuery As New ObjectQuery(Of Nullable(Of DateTime))(shipDateQueryString, context, MergeOption.NoTracking)
shipDateQuery.Parameters.Add(New ObjectParameter("contactId", contactId))
' Iterate through the collection of values.
For Each shipDate As Nullable(Of DateTime) In shipDateQuery
Dim shipDateMessage As String = "date not set"
If shipDate IsNot Nothing Then
shipDateMessage = shipDate.ToString()
End If
Console.WriteLine("Ship Date: {0}.", shipDateMessage)
Next
End Using
int contactId = 377;
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
string orderQueryString = @"SELECT VALUE Length(order.PurchaseOrderNumber)
FROM AdventureWorksEntities.SalesOrderHeaders AS order
WHERE order.CustomerID = @contactId";
string shipDateQueryString = @"SELECT VALUE order.ShipDate
FROM AdventureWorksEntities.SalesOrderHeaders AS order
WHERE order.CustomerID = @contactId";
// Use the SelectValue method to select a value.
ObjectQuery<Int32> orderQuery =
new ObjectQuery<Int32>(orderQueryString,
context, MergeOption.NoTracking);
orderQuery.Parameters.Add(
new ObjectParameter("contactId", contactId));
// Iterate through the collection of values.
foreach (Int32 result in orderQuery)
{
Console.WriteLine("{0}", result);
}
// Use a nullable DateTime value because ShipDate can be null.
ObjectQuery<Nullable<DateTime>> shipDateQuery =
new ObjectQuery<Nullable<DateTime>>(shipDateQueryString,
context, MergeOption.NoTracking);
shipDateQuery.Parameters.Add(
new ObjectParameter("contactId", contactId));
// Iterate through the collection of values.
foreach (Nullable<DateTime> shipDate in shipDateQuery)
{
string shipDateMessage = "date not set";
if (shipDate != null)
{
shipDateMessage = shipDate.ToString();
}
Console.WriteLine("Ship Date: {0}.", shipDateMessage);
}
}
L'exemple ci-dessous utilise la méthode du Générateur de requêtes.
Dim contactId As Integer = 377
Using context As New AdventureWorksEntities()
' Use the SelectValue method to select a value.
Dim orderQuery As ObjectQuery(Of Int32) = context.SalesOrderHeaders.Where("it.CustomerID = @contactId", _
New ObjectParameter("contactId", contactId)).SelectValue(Of Int32)("Length(it.PurchaseOrderNumber)")
' Iterate through the collection of values.
For Each result As Int32 In orderQuery
Console.WriteLine("{0}", result)
Next
' Use a nullable DateTime value because ShipDate can be null.
Dim shipDateQuery As ObjectQuery(Of Nullable(Of DateTime)) = _
context.SalesOrderHeaders.Where("it.CustomerID = @contactId", _
New ObjectParameter("contactId", contactId)).SelectValue(Of Nullable(Of DateTime))("it.ShipDate")
' Iterate through the collection of values.
For Each shipDate As Nullable(Of DateTime) In shipDateQuery
Dim shipDateMessage As String = "date not set"
If shipDate IsNot Nothing Then
shipDateMessage = shipDate.ToString()
End If
Console.WriteLine("Ship Date: {0}.", shipDateMessage)
Next
End Using
int contactId = 377;
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
// Use the SelectValue method to select a value.
ObjectQuery<Int32> orderQuery =
context.SalesOrderHeaders
.Where("it.CustomerID = @contactId",
new ObjectParameter("contactId", contactId))
.SelectValue<Int32>("Length(it.PurchaseOrderNumber)");
// Iterate through the collection of values.
foreach (Int32 result in orderQuery)
{
Console.WriteLine("{0}", result);
}
// Use a nullable DateTime value because ShipDate can be null.
ObjectQuery<Nullable<DateTime>> shipDateQuery =
context.SalesOrderHeaders
.Where("it.CustomerID = @contactId",
new ObjectParameter("contactId", contactId))
.SelectValue<Nullable<DateTime>>("it.ShipDate");
// Iterate through the collection of values.
foreach (Nullable<DateTime> shipDate in shipDateQuery)
{
string shipDateMessage = "date not set";
if (shipDate != null)
{
shipDateMessage = shipDate.ToString();
}
Console.WriteLine("Ship Date: {0}.", shipDateMessage);
}
}
Voir aussi
Tâches
Procédure : exécuter une requête qui retourne des objets de type d'entité (Entity Framework)
Procédure : exécuter une requête qui retourne une collection de types anonymes (Entity Framework)
Procédure : exécuter une requête paramétrable (Entity Framework)