How to: Enable Database Storage for User-Defined Criteria that Filter a List View

• Apr 19, 2024
• 5 minutes to read

This topic demonstrates how to design and save filtering criteria at runtime in an XAF application. The scenario consists of two steps:

1. Define the FilteringCriterion business class that implements filtering criteria for a List View.
2. Create a custom View Controller that contains an Action used to filter the List View.

Note

To follow the instructions in this topic, you can use the MainDemo.NET application installed with the XAF package. The default location of the application is %PUBLIC%\Documents\DevExpress Demos 23.2\Components\XAF.

Step 1 - Define the FilteringCriterion Business Class

1. Add a class to the BusinessObjects folder of the MainDemo.Module project and name it FilteringCriterion.cs. Replace auto-generated code with the following class declaration:

   C# (EF Core)

   using System.ComponentModel;
   using System.ComponentModel.DataAnnotations.Schema;
   using DevExpress.ExpressApp;
   using DevExpress.ExpressApp.DC;
   using DevExpress.ExpressApp.Editors;
   using DevExpress.Persistent.Base;
   using DevExpress.Persistent.BaseImpl.EF;
   
   namespace MainDemo.Module.BusinessObjects {
       [DefaultClassOptions, ImageName("Action_Filter")]
       public class FilteringCriterion : BaseObject {
           private Type objectType;
   
           public virtual string Description { get; set; }
   
           [Browsable(false)]
           public virtual string ObjectTypeName {
               get { return objectType == null ? string.Empty : objectType.FullName; }
               set {
                   ITypeInfo typeInfo = XafTypesInfo.Instance.FindTypeInfo(value);
                   objectType = typeInfo == null ? null : typeInfo.Type;
               }
           }
   
           [NotMapped, ImmediatePostData]
           public Type ObjectType {
               get { return objectType; }
               set {
                   if(objectType == value)
                       return;
                   objectType = value;
                   Criterion = string.Empty;
               }
           }
   
           [CriteriaOptions(nameof(ObjectType))]
           [FieldSize(FieldSizeAttribute.Unlimited)]
           [EditorAlias(EditorAliases.PopupCriteriaPropertyEditor)]
           public virtual string Criterion { get; set; }
       }
   }
   

   C# (XPO)

   using System.ComponentModel;
   using System.ComponentModel.DataAnnotations.Schema;
   using DevExpress.ExpressApp;
   using DevExpress.ExpressApp.DC;
   using DevExpress.ExpressApp.Editors;
   using DevExpress.Persistent.Base;
   using DevExpress.Persistent.BaseImpl.EF;
   
   namespace MainDemo.Module.BusinessObjects {
       [DefaultClassOptions, ImageName("Action_Filter")]
       public class FilteringCriterion : BaseObject {
           private Type objectType;
   
           public virtual string Description { get; set; }
   
           [Browsable(false)]
           public virtual string ObjectTypeName {
               get { return objectType == null ? string.Empty : objectType.FullName; }
               set {
                   ITypeInfo typeInfo = XafTypesInfo.Instance.FindTypeInfo(value);
                   objectType = typeInfo == null ? null : typeInfo.Type;
               }
           }
   
           [NotMapped, ImmediatePostData]
           public Type ObjectType {
               get { return objectType; }
               set {
                   if(objectType == value)
                       return;
                   objectType = value;
                   Criterion = string.Empty;
               }
           }
   
           [CriteriaOptions(nameof(ObjectType))]
           [FieldSize(FieldSizeAttribute.Unlimited)]
           [EditorAlias(EditorAliases.PopupCriteriaPropertyEditor)]
           public virtual string Criterion { get; set; }
       }
   }
   

   Objects of this class implement filtering criteria.

   The Description field contains the text that describes a criterion. These descriptions are used to fill a drop-down list of possible filters.

   The Criterion property contains a criterion. To use the built-in XAF Criteria Property Editors, the property that contains a criterion must have a CriteriaOptionsAttribute. The attribute’s parameter is the name of an additional Type property that specifies the target object type. In this sample, it is the ObjectType property. Additionally, an EditorAliasAttribute with the PopupCriteriaPropertyEditor alias is applied to the Criterion property. This attribute changes the default Property Editor for the property:

   • PopupFilterPropertyEditor for ASP.NET Core Blazor applications
   • PopupCriteriaPropertyEditor for Windows Forms applications
   • ASPxPopupCriteriaPropertyEditor for ASP.NET Web Forms applications

2. Optional. If you use Entity Framework Core, register the FilteringCriterion type in DbContext:

   using DevExpress.ExpressApp.Design;
   using DevExpress.ExpressApp.EFCore.DesignTime;
   using DevExpress.Persistent.Base;
   using Microsoft.EntityFrameworkCore;
   using Microsoft.EntityFrameworkCore.Design;
   
   namespace MainDemo.Module.BusinessObjects;
   
   //..
   
   [TypesInfoInitializer(typeof(MainDemoDbContextContextInitializer))]
   public class MainDemoDbContext : DbContext {
       public MainDemoDbContext(DbContextOptions<MainDemoDbContext> options) : base(options) {
       }
       public DbSet<FilteringCriterion> FilteringCriteria { get; set; }
   
       // ...
   }
   

   Add a migration and update the database. See the following section for details: Use a DBMS: Setup Migrations.

Step 2 - Create a Custom List View Controller

1. Add the following CriteriaController class to the Controllers folder of the MainDemo.Module project:

   using DevExpress.ExpressApp;
   using DevExpress.ExpressApp.Actions;
   using DevExpress.Persistent.Base;
   using MainDemo.Module.BusinessObjects;
   
   namespace MainDemo.Module.Controllers {
       public class CriteriaController : ViewController<ListView> {
           private SingleChoiceAction filteringCriterionAction;
           public CriteriaController() {
               filteringCriterionAction = new SingleChoiceAction(
                   this, "FilteringCriterion", PredefinedCategory.Filters);
               filteringCriterionAction.Execute += FilteringCriterionAction_Execute;
           }
           protected override void OnActivated() {
               filteringCriterionAction.Items.Clear();
               foreach(FilteringCriterion criterion in ObjectSpace.GetObjects<FilteringCriterion>()) {
                   if(criterion.ObjectType.IsAssignableFrom(View.ObjectTypeInfo.Type)) {
                       filteringCriterionAction.Items.Add(new ChoiceActionItem(criterion.Description, criterion.Criterion));
                   }
               }
               if(filteringCriterionAction.Items.Count > 0) {
                   filteringCriterionAction.Items.Add(new ChoiceActionItem("All", null));
               }
           }
           private void FilteringCriterionAction_Execute(object sender, SingleChoiceActionExecuteEventArgs e) {
               var collectionSource = View.CollectionSource;
               collectionSource.BeginUpdateCriteria();
               collectionSource.Criteria.Clear();
               collectionSource.Criteria[e.SelectedChoiceActionItem.Caption] = ObjectSpace.ParseCriteria(e.SelectedChoiceActionItem.Data as string);
               collectionSource.EndUpdateCriteria();
           }
       }
   }
   

   This Controller adds the FilteringCriterion SingleChoiceAction and populates the Action’s dropdown list with all existing FilterCriterion objects whose ObjectType matches the type of objects displayed in the current List View.

   The FilteringCriterion Action applies the criterion selected in the dropdown list to the List View. To convert the Criterion property’s value of a FilterCriterion object to the DevExpress.Data.Filtering.CriteriaOperator object, you need to call the static CriteriaEditorHelper.GetCriteriaOperator method. This method takes three parameters. The string parameter is the criterion to be converted. The Type parameter specifies the object type for which the criterion is constructed. The ObjectSpace parameter specifies any IObjectSpace that contains objects of the specified type.

   Note

   You should not use the CriteriaOperator.Parse method in this scenario. Criteria Property Editors can generate Criteria Strings containing Object Parameters, which are specific to XAF and cannot be parsed by CriteriaOperator.Parse.

2. Run the application, create several business objects, and then try the FilteringCriterion action.

   ASP.NET Core Blazor

   

   Windows Forms

   

You can also review Criteria Property Editors in the Property Editors | Criteria Properties section in the Feature Center demo installed with XAF. The default location of the application is %PUBLIC%\Documents\DevExpress Demos 23.2\Components\XAF\FeatureCenter.NETFramework.XPO.