Load Objects
- 6 minutes to read
In your business logic you may need to fetch another object or a collection of objects to calculated values based on that object properties. You can implement the logic to obtain an existing object in a Controller or in a business class.
Load Objects in a Controller
Object Space exposes the following methods to find an existing object.
- IObjectSpace.FirstOrDefault<ObjectType>
- Searches for the first object that matches the specified lambda expression. The generic parameter determines the object’s type.
- IObjectSpace.FindObject
- Searches for the first object that matches the specified criteria and is of the specified type.
- IObjectSpace.FindObject<ObjectType>
- Searches for the first object that matches the specified criteria. The object’s type is designated by the specified generic type parameter.
- IObjectSpace.GetObject
- Retrieves an object that corresponds to an IObjectRecord wrapper or object from another Object Space.
- IObjectSpace.GetObjectByKey
- Returns the persistent object that has the specified value for its key property.
- IObjectSpace.GetObjectByKey<ObjectType>
- Returns a persistent object of the type designated by the specified generic type parameter, with the specified value for its key property.
- IObjectSpace.GetObjectByHandle
- Returns the object with the specified handle.
- IObjectSpace.IsObjectFitForCriteria
- Specifies whether the specified object satisfies the specified criteria.
The following Object Space methods return a collection of objects.
- IObjectSpace.GetObjects
- Retrieves objects of the specified type from the current Object Space. Returns an IList collection.
- IObjectSpace.GetObjects<T>
- Retrieves objects of the specified type from the current Object Space. Returns an IList collection.
- IObjectSpace.CreateCollection
- Creates and initializes a collection of objects of the specified type, filtered according to the specified criteria and sorted according to the given sorting list.
- IObjectSpace.GetObjectsQuery<T>
- Gets a queryable data structure that provides functionality to evaluate queries against a specific business object type.
The following example uses a Parametrized Action to search for a Person by LastName, and then assigns all deferred tasks to that person.
using System.Collections;
using DevExpress.Data.Filtering;
using DevExpress.ExpressApp;
using DevExpress.ExpressApp.Actions;
using DevExpress.Persistent.Base;
using DevExpress.Persistent.Base.General;
using DevExpress.Persistent.BaseImpl;
// ...
public class AssignTasksController : ObjectViewController<ListView, MainDemo.Module.BusinessObjects.DemoTask> {
public AssignTasksController() {
ParametrizedAction assignTasksAction = new ParametrizedAction(
this, "AssignTasks", PredefinedCategory.Edit, typeof(string));
assignTasksAction.Execute += AssignTasksAction_Execute;
}
private void AssignTasksAction_Execute(object sender, ParametrizedActionExecuteEventArgs e) {
IObjectSpace objectSpace = View.ObjectSpace;
string personParamValue = e.ParameterCurrentValue as string;
CriteriaOperator personCriteria = CriteriaOperator.Parse("Contains([LastName], ?)", personParamValue);
Person person = (Person)objectSpace.FindObject(typeof(Person), personCriteria);
if(person != null) {
CriteriaOperator taskCriteria = CriteriaOperator.Parse("[Status] = ?", TaskStatus.Deferred);
IList tasks = objectSpace.GetObjects(
typeof(MainDemo.Module.BusinessObjects.DemoTask), taskCriteria);
foreach(MainDemo.Module.BusinessObjects.DemoTask task in tasks) {
task.AssignedTo = person;
}
}
}
}
You can use the IObjectSpace.GetObjectsQuery<T> method to load objects. It allows you to use LINQ expressions to specify the required request.
Business logic can depend on a number of records in a database. In this scenario, use the IObjectSpace.GetObjectsCount method to get a number of records without fetching records.
In a Data Model (in an XPO Business Class)
An XPO Session available via the Session property in a business class implements methods to find and read an object from a database.
The following code snippet demonstrates how to initialize Employee‘s Address1 and Manager reference properties with new and existing objects:
File: MySolution.Module\BusinessObjects\Contact.cs(.vb).
using DevExpress.Data.Filtering;
using DevExpress.Persistent.BaseImpl;
using DevExpress.Xpo;
// ...
public class Employee : Person {
//...
public override void AfterConstruction() {
base.AfterConstruction();
Address1 = new Address(Session);
Address1.Country = Session.FindObject<Country>(CriteriaOperator.Parse("Name = 'USA'"));
if(Address1.Country == null) {
Address1.Country = new Country(Session);
Address1.Country.Name = "USA";
}
Manager = Session.FindObject<Employee>(CriteriaOperator.Parse(
"FirstName = 'John' && LastName = 'Doe'"));
}
}
To get a collection of objects in an XPO business class, instantiate a new XPCollection.
using DevExpress.Persistent.BaseImpl;
using DevExpress.Xpo;
// ...
public class Order : BaseObject {
private XPCollection<Accessory> fAvailableAccessories;
public XPCollection<Accessory> AvailableAccessories {
get {
if (fAvailableAccessories == null) {
fAvailableAccessories = new XPCollection<Accessory>(Session);
}
return fAvailableAccessories;
}
}
}
public class Accessory : BaseObject { }
It’s possible to use the Session methods like GetObjects to fetch a collection of objects.
In an EF Core Business Class
Inside an EF Core business class, implement the IObjectSpaceLink interface in the class. XAF will automatically assign an Object Space instance to the IObjectSpaceLink.ObjectSpace property. Use the assigned Object Space APIs listed above to get an existing object.
The following code snippet demonstrates how to initialize Employee‘s Address1 and Manager reference properties with new and existing objects:
File: MySolution.Module\BusinessObjects\Employee.cs.
using DevExpress.ExpressApp;
using DevExpress.Persistent.BaseImpl;
// ...
public class Employee : Person, IXafEntityObject, IObjectSpaceLink {
//...
void IXafEntityObject.OnCreated() {
// ...
Address1 = objectSpace.CreateObject<Address>();
Address1.Country = objectSpace.FirstOrDefault<Country>(c => c.Name == "USA");
if (Address1.Country == null) {
Address1.Country = objectSpace.CreateObject<Country>();
Address1.Country.Name = "USA";
}
Manager = objectSpace.FirstOrDefault<Employee>(e => e.FirstName == "John" && e.LastName == "Doe");
}
void IXafEntityObject.OnLoaded() { }
void IXafEntityObject.OnSaving() { }
private IObjectSpace objectSpace;
IObjectSpace IObjectSpaceLink.ObjectSpace {
get { return objectSpace; }
set { objectSpace = value; }
}
}