The ”delete-orphans” option is a boolean class-level option to control the automatic deletion of certain types of unreferenced instances. If the delete-orphans extension is set to true, and the class is involved on the ‘many side’ of a relation, then it is deleted on commit if all of the reference fields used on the opposite side of the relationship(s) are null.
For example let’s take the parent/child relationship between Order and OrderDetails: the order should have a collection of order details.
| C# |
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[Telerik.OpenAccess.Persistent()]
class Order
{
private IList<OrderDetail> orderDetails = new List<OrderDetail>();
public IList<OrderDetail> OrderDetails
{
get
{
return orderDetails;
}
set
{
orderDetails = value;
}
}
}
[Telerik.OpenAccess.Persistent()]
class OrderDetail
{
public string name;
} |
| VB.NET |
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<Telerik.OpenAccess.Persistent()> _
Friend Class Order
Private orderLines_Renamed As IList(Of OrderDetail) = New List(Of OrderDetail)()
Public Property OrderLines() As IList(Of OrderDetail)
Get
Return orderLines_Renamed
End Get
Set(ByVal value As IList(Of OrderDetail))
orderLines_Renamed = value
End Set
End Property
End Class
<Telerik.OpenAccess.Persistent()> _
Friend Class OrderDetail
Public name As String
End Class |
When you remove an item from the collection of the order object (without removing it from the scope) and commit, then the order detail instance will be left without a parent (aka orphan). In this case we removed the item from the collection but it still exists in the database. If the delete orphan is active then this order detail will be removed from the database as well (else it will still reside in the database even though it is not linked to anything).
| C# |
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IObjectScope scope = ObjectScopeProvider1.GetNewObjectScope();
scope.Transaction.Begin();
Order o = scope.Extent<Order>().First();
//In case of Clear() all the data from OrderDetails table will
//be deleted from the database.
//if the delete-orphans is set to true.
o.OrderDetails.Clear();
scope.Transaction.Commit(); |
| VB.NET |
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Dim scope As IObjectScope = ObjectScopeProvider1.GetNewObjectScope()
scope.Transaction.Begin()
Dim o As Order = scope.Extent(Of Order)().First()
o.OrderDetails.Clear()
scope.Transaction.Commit() |
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The both examples will remove only instance if you use Remove method instead of Clear. |
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If you use this option you should not set the references to the persistent values in a collection as dependent; as instances used by one collection might be deleted when the other collection is deleted, which will cause an ObjectNotFoundException when the collection is retrieved. |
The XML metadata for the same is given below:
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<class name="OrderDetail">
<extension key="delete-orphans" value="true" />
</class>
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