How to: Initialize Business Objects with Default Property Values in Entity Framework Core

• Apr 19, 2024
• 6 minutes to read

When designing business classes, a common task is to ensure that a newly created business object is initialized with default property values. This topic explains how different types of properties can be initialized. As an example, a Contact business class will be implemented. After a Contact object is created, its properties will be initialized with default values.

Simple Property

You can support an IXafEntityObject interface in your business classes. This interface declares the IXafEntityObject.OnCreated method intended for object initialization. The OnCreated method is called only once for an object - after the object is created. Whenever you need to initialize an object, place the initialization code into the OnCreated method body. The following code snippet demonstrates how simple value properties can be initialized.

using DevExpress.ExpressApp;
using DevExpress.Persistent.BaseImpl.EF;
// ...
public class Contact : IXafEntityObject {
    //...
    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }
    public virtual TitleOfCourtesy TitleOfCourtesy { get; set; }
    public virtual IList<PhoneNumber> PhoneNumbers { get; set; } = new ObservableCollection<PhoneNumber>();
    //...
    void IXafEntityObject.OnCreated() {
        FirstName = "Sam";
        TitleOfCourtesy = TitleOfCourtesy.Mr;
    }
    void IXafEntityObject.OnLoaded() { }
    void IXafEntityObject.OnSaving() { }
}

public class PhoneNumber : BaseObject {
    public virtual string Number { get; set; }
    public virtual string PhoneType { get; set; }
    public virtual Contact Contact { get; set; }
    // ...
}

public enum TitleOfCourtesy {
    Dr,
    Miss,
    Mr,
    Mrs,
    Ms
};

// Make sure that you use options.UseChangeTrackingProxies() in your DbContext settings.

You can also inherit your class from the DevExpress.Persistent.BaseImpl.EF.BaseObject class that implements the IXafEntityObject interface:

using DevExpress.ExpressApp;
using DevExpress.ExpressApp.DC;
using DevExpress.Persistent.BaseImpl.EF;
using MainDemo.Module.BusinessObjects;
using System.Collections.ObjectModel;
public class ContactBase2 : BaseObject {
    //...
    public virtual string FirstName { get; set; }
    public virtual string LastName { get; set; }
    public virtual TitleOfCourtesy TitleOfCourtesy { get; set; }
    public virtual IList<PhoneNumber> PhoneNumbers { get; set; } = new ObservableCollection<PhoneNumber>();
    //...
    public override void OnCreated() {
        FirstName = "Sam";
        TitleOfCourtesy = TitleOfCourtesy.Mr;
    }
}

To see another example of initializing a simple property, refer to the Initialize Business Object Properties (EF Core) tutorial lesson.

Reference Property

Initialization of reference properties differs from initialization of simple properties, primarily in that you may need to obtain a reference to an existing object. For this purpose, use the IObjectSpace.FindObject method of the object’s Object Space. To access the Object Space from the business object code, you should support the IObjectSpaceLink interface.

The following code snippet demonstrates how to initialize the Address1 reference property with a new or existing object:

File: MySolution.Module\BusinessObjects\Employee.cs

using DevExpress.Data.Filtering;
using DevExpress.ExpressApp;
using DevExpress.Persistent.Base;
using DevExpress.Persistent.BaseImpl.EF;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace YourSolutionName.Module.BusinessObjects;
[DefaultClassOptions]
public class Employee : IXafEntityObject {
    [Key]
    public virtual Guid ID { get; set; }

    public virtual string Manager { get; set; }
    public void OnCreated() {
        // ...
        var address = ObjectSpace.FindObject<Address>(CriteriaOperator.FromLambda<Address>(a => a.Country == "USA"));
        if(address == null) {
            address = ObjectSpace.CreateObject<Address>();
            address.Country = "USA";
        }
        Address1 = address;
    }
    public virtual Address Address1 { get; set; }
    public void OnLoaded() { }
    public void OnSaving() { }
    public IObjectSpace ObjectSpace {
        get {
            return ((IObjectSpaceLink)this).ObjectSpace;
        }
    }
}
[DefaultClassOptions]
[DefaultProperty(nameof(Country))]
public class Address : BaseObject {
    public virtual string Country { get; set; }
    // ...
}
// Make sure that you use options.UseChangeTrackingProxies() in your DbContext settings.

Alternatively, you can inherit your class from the DevExpress.Persistent.BaseImpl.EF.BaseObject class as follows:

using DevExpress.Data.Filtering;
using DevExpress.ExpressApp;
using DevExpress.Persistent.Base;
using DevExpress.Persistent.BaseImpl.EF;
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.ComponentModel.DataAnnotations;
using System.Linq;
using System.Text;
using System.Threading.Tasks;
namespace YourSolutionName.Module.BusinessObjects;
[DefaultClassOptions]
public class Employee : BaseObject {
    public virtual string Manager { get; set; }
    public override void OnCreated() {
        // ...
        var address = ObjectSpace.FindObject<Address>(CriteriaOperator.FromLambda<Address>(a => a.Country == "USA"));
        if(address == null) {
            address = ObjectSpace.CreateObject<Address>();
            address.Country = "USA";
        }
        Address1 = address;
    }
    public virtual Address Address1 { get; set; }

}
[DefaultClassOptions]
[DefaultProperty(nameof(Country))]
public class Address : BaseObject {
    public virtual string Country { get; set; }
    // ...
}


// Make sure that you use options.UseChangeTrackingProxies() in your DbContext settings.

Collection Property

The following code snippet demonstrates how to populate the Phones collection with predefined phone numbers.

using DevExpress.ExpressApp;
using DevExpress.ExpressApp.DC;
using DevExpress.Persistent.BaseImpl.EF;
using MainDemo.Module.BusinessObjects;
using System.Collections.ObjectModel;
//...
public class Contact : IXafEntityObject {
    //...
    void IXafEntityObject.OnCreated() {
        // ...
        PhoneNumber phone1 = ObjectSpace.FirstOrDefault<PhoneNumber>(
            n => n.Number == "555-0101");
        PhoneNumber phone2 = ObjectSpace.FirstOrDefault<PhoneNumber>(
            n => n.Number == "555-0102");
        if(phone1 != null) { PhoneNumbers.Add(phone1); }
        if(phone2 != null) { PhoneNumbers.Add(phone2); }
    }
    [Aggregated]
    public virtual IList<PhoneNumber> PhoneNumbers { get; set; } = new ObservableCollection<PhoneNumber>();
    void IXafEntityObject.OnLoaded() { }
    void IXafEntityObject.OnSaving() { }

    IObjectSpace ObjectSpace {
        get { return ((IObjectSpaceLink)this).ObjectSpace; }
    }
}

You can also create a BaseObject descendant:

using DevExpress.ExpressApp.DC;
using DevExpress.Persistent.BaseImpl.EF;
using MainDemo.Module.BusinessObjects;
using System.Collections.ObjectModel;
//...
public class ContactBase : BaseObject {
    //...
    public override void OnCreated() {
        // ...
        PhoneNumber phone1 = ObjectSpace.FirstOrDefault<PhoneNumber>(
            n => n.Number == "555-0101");
        PhoneNumber phone2 = ObjectSpace.FirstOrDefault<PhoneNumber>(
            n => n.Number == "555-0102");
        if(phone1 != null) { PhoneNumbers.Add(phone1); }
        if(phone2 != null) { PhoneNumbers.Add(phone2); }
    }
    [Aggregated]
    public virtual IList<PhoneNumber> PhoneNumbers { get; set; } = new ObservableCollection<PhoneNumber>();
}

Calculated Property

A calculated property value is automatically updated when the associated property values are changed. To learn how to implement a regular calculated property, refer to the Create a Calculated Property tutorial lesson. To learn how to implement a calculated property based on property values of the objects contained in a child object collection.

Initialize an Object Created via the New Action

In certain scenarios, you may need to initialize only objects created specifically via the New Action. To learn how to do this, refer to the How to: Initialize an Object Created Using the New Action help topic.

Initialize a Property of a Child Object with a Value Taken from a Master Object

You can set the default value for the child object’s property within the setter of a property that refers to the master object.

public class ChildObject {
    // ...
    public virtual MasterObject MasterObject {
        get { return masterObject; }
        set {
            if (master == value) return;
            masterObject = value;
            if (value != null) {
                this.SomeProperty = value.DefaultForChildren;
            }
        }
    }
}

Since the reference property of a child object will not be initialized until committing changes, it is necessary to use a ViewController to initialize the child object depending on the master object (see How to: Initialize an Object Created Using the New Action).