Gewusst wie: Seitenweise durch Abfrageresultate navigieren (Entity Framework)
In diesem Thema wird gezeigt, wie Sie seitenweise durch die Resultate einer Abfrage navigieren können. Im Beispiel werden fünf Product-Objekte abgerufen, nachdem die ersten drei Objekte im Abfrageresultat übersprungen wurden, wobei das Abfrageresultat nach Product.ListPrice geordnet ist. Dasselbe Beispiel wird nach Verwendung der folgenden Entity Framework-Abfragetechnologien gezeigt:
LINQ-to-Entities
Entity SQL mit ObjectQuery<T>
Abfrage-Generator-Methoden von ObjectQuery<T>
Das Beispiel in diesem Thema beruht auf dem Adventure Works Sales-Modell. Zum Ausführen des Codes in diesem Thema muss dem Projekt bereits das Adventure Works Sales-Modell hinzugefügt und das Projekt zur Verwendung von Entity Framework konfiguriert worden sein. Weitere Informationen finden Sie unter Gewusst wie: Verwenden des Assistenten für Entity Data Model (Entity Framework) bzw. Gewusst wie: Manuelles Konfigurieren eines Entity Framework-Projekts und Gewusst wie: Manuelles Definieren eines Entity Data Model (Entity Framework).
Beispiel
Dies ist das LINQ to Entities -Beispiel.
Using context As New AdventureWorksEntities
'LINQ to Entities only supports Skip on ordered collections.
Dim products As IOrderedQueryable(Of Product) = _
context.Products.OrderBy(Function(p) p.ListPrice)
Dim allButFirst3Products As IQueryable(Of Product) = products.Skip(3)
Console.WriteLine("All but first 3 products:")
For Each product As Product In allButFirst3Products
Console.WriteLine("Name: {0} \t ID: {1}", _
product.Name, _
product.ProductID)
Next
End Using
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
// LINQ to Entities only supports Skip on ordered collections.
IOrderedQueryable<Product> products = context.Products
.OrderBy(p => p.ListPrice);
IQueryable<Product> allButFirst3Products = products.Skip(3);
Console.WriteLine("All but first 3 products:");
foreach (Product product in allButFirst3Products)
{
Console.WriteLine("Name: {0} \t ID: {1}",
product.Name,
product.ProductID);
}
}
Dies ist das Entity SQL -Beispiel.
Using context As New AdventureWorksEntities()
' Create a query that takes two parameters.
Dim queryString As String = "SELECT VALUE product FROM AdventureWorksEntities.Products AS product " & _
" order by product.ListPrice SKIP @skip LIMIT @limit"
Dim productQuery As New ObjectQuery(Of Product)(queryString, context)
' Add parameters to the collection.
productQuery.Parameters.Add(New ObjectParameter("skip", 3))
productQuery.Parameters.Add(New ObjectParameter("limit", 5))
' Iterate through the collection of Contact items.
For Each result As Product In productQuery
Console.WriteLine("ID: {0}; Name: {1}", result.ProductID, result.Name)
Next
End Using
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
// Create a query that takes two parameters.
string queryString =
@"SELECT VALUE product FROM
AdventureWorksEntities.Products AS product
order by product.ListPrice SKIP @skip LIMIT @limit";
ObjectQuery<Product> productQuery =
new ObjectQuery<Product>(queryString, context);
// Add parameters to the collection.
productQuery.Parameters.Add(new ObjectParameter("skip", 3));
productQuery.Parameters.Add(new ObjectParameter("limit", 5));
// Iterate through the collection of Contact items.
foreach (Product result in productQuery)
Console.WriteLine("ID: {0}; Name: {1}",
result.ProductID, result.Name);
}
Dies ist das Beispiel für die Abfrage-Generator-Methode.
Using context As New AdventureWorksEntities()
' Define the parameters used to define the "page" of returned data.
Dim skipValue As Integer = 3
Dim limitValue As Integer = 5
' Define a query that returns a "page" or the full
' Product data using the Skip and Top methods.
' When Top() follows Skip(), it acts like the LIMIT statement.
Dim query As ObjectQuery(Of Product) = _
context.Products.Skip("it.ListPrice", "@skip", _
New ObjectParameter("skip", skipValue)).Top("@limit", New ObjectParameter("limit", limitValue))
' Iterate through the page of Product items.
For Each result As Product In query
Console.WriteLine("ID: {0}; Name: {1}", result.ProductID, result.Name)
Next
End Using
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
// Define the parameters used to define the "page" of returned data.
int skipValue = 3;
int limitValue = 5;
// Define a query that returns a "page" or the full
// Product data using the Skip and Top methods.
// When Top() follows Skip(), it acts like the LIMIT statement.
ObjectQuery<Product> query = context.Products
.Skip("it.ListPrice", "@skip",
new ObjectParameter("skip", skipValue))
.Top("@limit", new ObjectParameter("limit", limitValue));
// Iterate through the page of Product items.
foreach (Product result in query)
Console.WriteLine("ID: {0}; Name: {1}",
result.ProductID, result.Name);
}
Siehe auch
Verweis
SKIP (Entity SQL)
LIMIT (Entity SQL)
Skip
Top