.NET Framework 4.5.2+
.NET Framework 4.5.2+
.NET Standard 2.0+

XPCollection.Add(Object) Method

Adds the specified persistent object to the XPCollection.

Namespace: DevExpress.Xpo

Assembly: DevExpress.Xpo.v21.1.dll


public int Add(
    object newObject


Name Type Description
newObject Object

The persistent object to add to the collection.


Type Description

The zero-based index position at which the new element is inserted.


A persistent object is an object that implements the IXPSimpleObject interface or has the PersistentAttribute attribute.

You cannot add an object whose type is not the same or not inherited from the type specified by the XPCollection.ObjectClassInfo property. Also you cannot add the same object more than once. Doing so does not lead to an exception, however the object will not be added to the collection.

While the XPCollection is loading, it contains objects that match specific criteria. When you add an object, the collection does not check whether it matches the criteria or not.


The following example demonstrates how to implement a one-to-many relationship between persistent objects, so that child objects are considered a part of their owner (when an owner is deleted, its aggregated objects will be automatically deleted; similarly, when an object is saved its aggregated objects will also be saved).

A one-to-many relationship is set up using the AssociationAttribute attribute. The AggregatedAttribute attribute is used to implement aggregation.

In this example, a Person object can have multiple addresses that are stored in the Person.Addresses collection. Each address in this collection is represented by an Address persistent class. The Person.Addresses property is marked with the AssociationAttribute and AggregatedAttribute attributes.

If you run the code below as is, the console output will be:

7654 Amsterdam Ave, New York, NY 555 Harbor Way, Santa Barbara, CA

If you remove the Aggregated attribute, the output will change to:

7654 Amsterdam Ave, New York, NY 7654 Amsterdam Ave, New York, NY

using System;
using System.Collections.Generic;
using System.Linq;
using DevExpress.Xpo;

namespace ConsoleApplication1 {
    public class Person : XPObject {
        public string Name {
            get { return fName; }
            set { SetPropertyValue(nameof(Name), ref fName, value); }
        string fName;

        [Association("PersonAddresses"), Aggregated]
        public XPCollection<Address> Addresses {
            get { return GetCollection<Address>(nameof(Addresses)); }

    public class Address : XPObject {
        public Person Owner {
            get { return fOwner; }
            set { SetPropertyValue(nameof(Owner), ref fOwner, value); }
        Person fOwner;

        public string AddressInfo {
            get { return fAddressInfo; }
            set { SetPropertyValue(nameof(AddressInfo), ref fAddressInfo, value); }
        string fAddressInfo;


    class Program {
        static void Main(string[] args) {
            // Create a new instance of the Person class
            Person person = new Person() { Name = "Andrew Smith" };
            // Add an address for the person.
            Address address = new Address() { AddressInfo = "7654 Amsterdam Ave, New York, NY" };

            // Save the created Person object. The contents of the Addresses collection will be saved as well.
            // Reload the object to verify if changes were saved.

            address.AddressInfo = "555 Harbor Way, Santa Barbara, CA";
            // Reload the object to verify if changes were saved.

See Also