Initieringsuttryck
Ett initieringsuttryck initierar ett nytt objekt. De flesta initieringsuttryck stöds, inklusive de flesta nya initieringsuttrycken C# 3.0 och Visual Basic 9.0. Följande typer kan initieras och returneras av en LINQ till entitetsfråga:
En samling med noll eller fler typinskrivna entitetsobjekt eller en projektion av komplexa typer som definieras i den konceptuella modellen.
CLR-typer som stöds av Entity Framework.
Infogade samlingar.
Anonyma typer.
Initiering av anonym typ visas i följande exempel i frågeuttryckssyntax:
Decimal totalDue = 200;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
var salesInfo =
from s in context.SalesOrderHeaders
where s.TotalDue >= totalDue
select new { s.SalesOrderNumber, s.TotalDue };
Console.WriteLine("Sales order numbers:");
foreach (var sale in salesInfo)
{
Console.WriteLine("Order number: " + sale.SalesOrderNumber);
Console.WriteLine("Total due: " + sale.TotalDue);
Console.WriteLine("");
}
}
Dim totalDue = 200
Using context As New AdventureWorksEntities()
Dim salesInfo = _
From s In context.SalesOrderHeaders _
Where s.TotalDue >= totalDue _
Select New With {s.SalesOrderNumber, s.TotalDue}
Console.WriteLine("Sales order numbers:")
For Each sale In salesInfo
Console.WriteLine("Order number: " & sale.SalesOrderNumber)
Console.WriteLine("Total due: " & sale.TotalDue)
Console.WriteLine("")
Next
End Using
Följande exempel i metodbaserad frågesyntax visar initiering av anonym typ:
Decimal totalDue = 200;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
var salesInfo =
context.SalesOrderHeaders
.Where(s => s.TotalDue >= totalDue)
.Select(s => new { s.SalesOrderNumber, s.TotalDue });
Console.WriteLine("Sales order numbers:");
foreach (var sale in salesInfo)
{
Console.WriteLine("Order number: " + sale.SalesOrderNumber);
Console.WriteLine("Total due: " + sale.TotalDue);
Console.WriteLine("");
}
}
Dim totalDue = 200
Using context As New AdventureWorksEntities()
Dim salesInfo = _
context.SalesOrderHeaders _
.Where(Function(s) s.TotalDue >= totalDue) _
.Select(Function(s) New With {s.SalesOrderNumber, s.TotalDue})
Console.WriteLine("Sales order numbers:")
For Each sale In salesInfo
Console.WriteLine("Order number: " & sale.SalesOrderNumber)
Console.WriteLine("Total due: " & sale.TotalDue)
Console.WriteLine("")
Next
End Using
Användardefinierad klassinitiering stöds också. Initieringsmönstret C# 3.0 och Visual Basic 9.0 stöds och förutsätter att egenskaps getter och setter är symmetriska. Följande exempel i frågeuttryckssyntaxen visar en anpassad klass som initieras i frågan:
class MyOrder { public string SalesOrderNumber; public DateTime? ShipDate; }
Class MyOrder
Public SalesOrderNumber As String
Public ShipDate As DateTime?
End Class
Decimal totalDue = 200;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
IQueryable<MyOrder> salesInfo =
from s in context.SalesOrderHeaders
where s.TotalDue >= totalDue
select new MyOrder
{
SalesOrderNumber = s.SalesOrderNumber,
ShipDate = s.ShipDate
};
Console.WriteLine("Sales order info:");
foreach (MyOrder order in salesInfo)
{
Console.WriteLine("Order number: " + order.SalesOrderNumber);
Console.WriteLine("Ship date: " + order.ShipDate);
Console.WriteLine("");
}
}
Dim totalDue = 200
Using context As New AdventureWorksEntities()
Dim salesInfo = _
From s In context.SalesOrderHeaders _
Where s.TotalDue >= totalDue _
Select New MyOrder With _
{ _
.SalesOrderNumber = s.SalesOrderNumber, _
.ShipDate = s.ShipDate _
}
Console.WriteLine("Sales order info:")
For Each order As MyOrder In salesInfo
Console.WriteLine("Order number: " & order.SalesOrderNumber)
Console.WriteLine("Ship date: " & order.ShipDate)
Console.WriteLine("")
Next
End Using
I följande exempel i metodbaserad frågesyntax visas en anpassad klass som initieras i frågan:
Decimal totalDue = 200;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
IQueryable<MyOrder> salesInfo =
context.SalesOrderHeaders
.Where(s => s.TotalDue >= totalDue)
.Select(s => new MyOrder
{
SalesOrderNumber = s.SalesOrderNumber,
ShipDate = s.ShipDate
});
Console.WriteLine("Sales order info:");
foreach (MyOrder order in salesInfo)
{
Console.WriteLine("Order number: " + order.SalesOrderNumber);
Console.WriteLine("Ship date: " + order.ShipDate);
Console.WriteLine("");
}
}
Dim totalDue = 200
Using context As New AdventureWorksEntities()
Dim salesInfo As IQueryable(Of MyOrder) = _
context.SalesOrderHeaders _
.Where(Function(s) s.TotalDue >= totalDue) _
.Select(Function(s) New MyOrder With _
{ _
.SalesOrderNumber = s.SalesOrderNumber, _
.ShipDate = s.ShipDate _
})
Console.WriteLine("Sales order info:")
For Each order As MyOrder In salesInfo
Console.WriteLine("Order number: " & order.SalesOrderNumber)
Console.WriteLine("Ship date: " & order.ShipDate)
Console.WriteLine("")
Next
End Using