How to: Create an EntityKey
The EntityKey class represents the key of an entity object. You can create an instance of EntityKey by using the class constructors, or you can use the static CreateEntityKey method of ObjectContext to generate an EntityKey for a specific object. The entity key is used to attach an object or to return a specific object from the data source. For more information, see Working with Entity Keys.
The examples in this topic are based on the Adventure Works Sales Model. To run the code in this example, you must have already added the AdventureWorks Sales Model to your project and configured your project to use the Entity Framework. To do this, complete the procedures in How to: Manually Configure an Entity Framework Project and How to: Manually Define the Model and Mapping Files.
Example
The following example creates an instance of EntityKey using a specified key/value pair and the qualified entity set name. This key is then used to retrieve the object itself.
Using context As New AdventureWorksEntities()
Dim entity As Object = Nothing
Dim entityKeyValues As IEnumerable(Of KeyValuePair(Of String, Object)) = _
New KeyValuePair(Of String, Object)() {New KeyValuePair(Of String, Object)("SalesOrderID", 43680)}
' Create the key for a specific SalesOrderHeader object.
Dim key As New EntityKey("AdventureWorksEntities.SalesOrderHeaders", entityKeyValues)
' Get the object from the context or the persisted store by its key.
If context.TryGetObjectByKey(key, entity) Then
Console.WriteLine("The requested " & entity.GetType().FullName & " object was found")
Else
Console.WriteLine("An object with this key could not be found.")
End If
End Using
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
Object entity = null;
IEnumerable<KeyValuePair<string, object>> entityKeyValues =
new KeyValuePair<string, object>[] {
new KeyValuePair<string, object>("SalesOrderID", 43680) };
// Create the key for a specific SalesOrderHeader object.
EntityKey key = new EntityKey("AdventureWorksEntities.SalesOrderHeaders", entityKeyValues);
// Get the object from the context or the persisted store by its key.
if (context.TryGetObjectByKey(key, out entity))
{
Console.WriteLine("The requested " + entity.GetType().FullName +
" object was found");
}
else
{
Console.WriteLine("An object with this key " +
"could not be found.");
}
}
For an independent association, use the method described in the following example to define a relationship. For a foreign key association, define relationships by setting the value of the foreign key properties on the dependent object. For more information, see Defining and Managing Relationships.
The following example creates an instance of EntityKey using a specified key name, key value, and the qualified entity set name. This key is then used to attach an object and define a relationship.
Using context As New AdventureWorksEntities()
Try
' Create the key that represents the order.
Dim orderKey As New EntityKey("AdventureWorksEntities.SalesOrderHeaders", "SalesOrderID", orderId)
' Create the stand-in SalesOrderHeader object
' based on the specified SalesOrderID.
Dim order As New SalesOrderHeader()
order.EntityKey = orderKey
' Assign the ID to the SalesOrderID property to matche the key.
order.SalesOrderID = CInt(orderKey.EntityKeyValues(0).Value)
' Attach the stand-in SalesOrderHeader object.
context.SalesOrderHeaders.Attach(order)
' Create a new SalesOrderDetail object.
' You can use the static CreateObjectName method (the Entity Framework
' adds this method to the generated entity types) instead of the new operator:
' SalesOrderDetail.CreateSalesOrderDetail(1, 0, 2, 750, 1, (decimal)2171.2942, 0, 0,
' Guid.NewGuid(), DateTime.Today));
Dim detail = New SalesOrderDetail With
{
.SalesOrderID = 0,
.SalesOrderDetailID = 0,
.OrderQty = 2,
.ProductID = 750,
.SpecialOfferID = 1,
.UnitPrice = CDec(2171.2942),
.UnitPriceDiscount = 0,
.LineTotal = 0,
.rowguid = Guid.NewGuid(),
.ModifiedDate = DateTime.Now
}
order.SalesOrderDetails.Add(detail)
context.SaveChanges()
Catch generatedExceptionName As InvalidOperationException
Console.WriteLine("Ensure that the key value matches the value of the object's ID property.")
Catch generatedExceptionName As UpdateException
Console.WriteLine("An error has occured. Ensure that an object with the '{0}' key value exists.", orderId)
End Try
End Using
using (AdventureWorksEntities context =
new AdventureWorksEntities())
{
try
{
// Create the key that represents the order.
EntityKey orderKey =
new EntityKey("AdventureWorksEntities.SalesOrderHeaders",
"SalesOrderID", orderId);
// Create the stand-in SalesOrderHeader object
// based on the specified SalesOrderID.
SalesOrderHeader order = new SalesOrderHeader();
order.EntityKey = orderKey;
// Assign the ID to the SalesOrderID property to matche the key.
order.SalesOrderID = (int)orderKey.EntityKeyValues[0].Value;
// Attach the stand-in SalesOrderHeader object.
context.SalesOrderHeaders.Attach(order);
// Create a new SalesOrderDetail object.
// You can use the static CreateObjectName method (the Entity Framework
// adds this method to the generated entity types) instead of the new operator:
// SalesOrderDetail.CreateSalesOrderDetail(1, 0, 2, 750, 1, (decimal)2171.2942, 0, 0,
// Guid.NewGuid(), DateTime.Today));
SalesOrderDetail detail = new SalesOrderDetail
{
SalesOrderID = orderId,
SalesOrderDetailID = 0,
OrderQty = 2,
ProductID = 750,
SpecialOfferID = 1,
UnitPrice = (decimal)2171.2942,
UnitPriceDiscount = 0,
LineTotal = 0,
rowguid = Guid.NewGuid(),
ModifiedDate = DateTime.Now
};
order.SalesOrderDetails.Add(detail);
context.SaveChanges();
}
catch (InvalidOperationException)
{
Console.WriteLine("Ensure that the key value matches the value of the object's ID property.");
}
catch (UpdateException)
{
Console.WriteLine("An error has occured. Ensure that an object with the '{0}' key value exists.",
orderId);
}
}
The following example creates an instance of EntityKey using key values from a detached object. This key is then used to retrieve an attached instance of the object.
Private Shared Sub ApplyItemUpdates(ByVal updatedItem As SalesOrderDetail)
' Define an ObjectStateEntry and EntityKey for the current object.
Dim key As EntityKey
Dim originalItem As Object
Using context As New AdventureWorksEntities()
' Create the detached object's entity key.
key = context.CreateEntityKey("SalesOrderDetails", updatedItem)
' Get the original item based on the entity key from the context
' or from the database.
If context.TryGetObjectByKey(key, originalItem) Then
' Call the ApplyCurrentValues method to apply changes
' from the updated item to the original version.
context.ApplyCurrentValues(key.EntitySetName, updatedItem)
End If
context.SaveChanges()
End Using
End Sub
private static void ApplyItemUpdates(SalesOrderDetail updatedItem)
{
// Define an ObjectStateEntry and EntityKey for the current object.
EntityKey key = default(EntityKey);
object originalItem = null;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
// Create the detached object's entity key.
key = context.CreateEntityKey("SalesOrderDetails", updatedItem);
// Get the original item based on the entity key from the context
// or from the database.
if (context.TryGetObjectByKey(key, out originalItem))
{
// Call the ApplyCurrentValues method to apply changes
// from the updated item to the original version.
context.ApplyCurrentValues(key.EntitySetName, updatedItem);
}
context.SaveChanges();
}
}
See Also
Tasks
How to: Return a Specific Object Using its Key