Collection Properties in XPO
- 4 minutes to read
The examples below illustrate how to implement collection properties in an XPO persistent class.
Different collection properties have different Actions in a UI. You can manage the New, Delete, Link, or Unlink Action’s visibility in the Model Editor. Set the List View’s AllowNew, AllowDelete, AllowLink, or AllowUnlink property to false to hide these Actions.
Note
Refer to the FeatureCenter demo to see an example on how to implement collection properties (see %PUBLIC%\Documents\DevExpress Demos 23.2\Components\XAF\FeatureCenter.NETFramework.XPO\CS\FeatureCenter.Module\PropertyEditors\CollectionPropertiesObject.cs).
A collection of the XPCollection type
[Association("CollectionProperties-AssociatedObject")]
public XPCollection<AssociatedObject> Association {
get { return GetCollection<AssociatedObject>(nameof(Association)); }
}
Refer to the Relationships Between Persistent Objects in Code and UI article for more information on associated collections in XPO.
An aggregated collection of the XPCollection type
[Association("CollectionProperties-AggregatedObject"), Aggregated]
public XPCollection<AggregatedObject> AggregatedAssociation {
get { return GetCollection<AggregatedObject>(nameof(AggregatedAssociation)); }
}
Refer to the Relationships Between Persistent Objects in Code and UI article for more information on aggregated collections in XPO.
A non-associated collection with persistent objects
Populate this collection with objects and implement custom logic used to manage them if the collection is not a part of the association. To hide or display the New and Link or Delete and Unlink Actions in a UI, decorate the collection property with the CollectionOperationSet attribute, and specify the AllowAdd and AllowRemove parameters.
A collection of the XPCollection type
The New, Delete, Link, and Unlink Actions are available for this collection. We recommend using this collection to display objects, and not to edit them in the UI. In the code snippet below, the CollectionOperationSet‘s AllowAdd and AllowRemove parameters are set to false to deny a user to change the collection in the UI:
private XPCollection<NoAssociationObject> noAssociation;
[CollectionOperationSet(AllowAdd = false, AllowRemove = false)]
public XPCollection<NoAssociationObject> NoAssociation {
get {
if(noAssociation == null) {
noAssociation = new XPCollection<NoAssociationObject>(Session);
}
return noAssociation;
}
}
You can use the Criteria property to filter collection objects, or set the LoadingEnabled property to false and add objects to the collection. Subscribe to the collection’s CollectionChanged event to implement the required logic for New, Delete, Link, and Unlink Actions.
A collection of the BindingList type
The New, Delete, Link, and Unlink Actions are available for this collection.
private BindingList<NoAssociationObject> persistentBindingList;
public BindingList<NoAssociationObject> PersistentBindingList {
get {
if(persistentBindingList == null) {
persistentBindingList = new BindingList<NoAssociationObject>();
foreach(NoAssociationObject obj in NoAssociation) {
persistentBindingList.Add(obj);
}
}
return persistentBindingList;
}
}
Subscribe to the collection’s ListChanged event to implement the required logic for New, Delete, Link, and Unlink Actions.
The BindingList collection with non-persistent objects
The New, Delete, Link, and Unlink Actions are not available for this collection if its master object is a persistent object. If the master object is non-persistent, the New and Delete Actions are available. To activate Link and Unlink, set the LinkUnlinkController.RequirePersistentType property to false and handle the CustomCreateLinkView event.
private BindingList<SomeObject> nonPersistentObjectBindingList;
private void EnsureNonPersistentObjectBindingList() {
if(nonPersistentObjectBindingList == null) {
nonPersistentObjectBindingList = new BindingList<SomeObject>();
// ...
}
}
public BindingList<SomeObject> NonPersistentBindingList {
get {
EnsureNonPersistentObjectBindingList();
return nonPersistentObjectBindingList;
}
}