QueryDescriptor Class

Visual Basic (Declaration)
Public Class QueryDescriptor

Visual Basic (Usage)	Copy Code
Dim instance As QueryDescriptor

C#
public class QueryDescriptor

Delphi
public class QueryDescriptor

JScript
public class QueryDescriptor

Managed Extensions for C++
public __gc class QueryDescriptor

C++/CLI
public ref class QueryDescriptor

The following example shows how to instantiate a QueryDescriptor programmatically and demonstrate the use of FilterDescriptor, SortDescriptor and PageDescriptor in the QueryDescriptor object.

CS	Copy Code
QueryDescriptor queryDescriptor = new QueryDescriptor(); // filtering // get records that have // (UnitPrice >= 0 AND UnitPrice < 50) OR (UnitPrice == 0) CompositeFilterDescriptorCollection groupFilter1 = new CompositeFilterDescriptorCollection(); groupFilter1.LogicalOperator = FilterCompositionLogicalOperator.And; groupFilter1.Add( new FilterDescriptor() { PropertyName = "UnitPrice", Operator = FilterOperator.IsGreaterThanOrEqualTo, Value = 0 } ); groupFilter1.Add( new FilterDescriptor() { PropertyName = "UnitPrice", Operator = FilterOperator.IsLessThan, Value = 50 } ); CompositeFilterDescriptorCollection groupFilter2 = new CompositeFilterDescriptorCollection(); groupFilter2.LogicalOperator = FilterCompositionLogicalOperator.And; groupFilter2.Add( new FilterDescriptor() { PropertyName = "UnitsInStock", Operator = FilterOperator.IsEqualTo, Value = 0 } ); queryDescriptor.FilterDescriptors.LogicalOperator = FilterCompositionLogicalOperator.Or; queryDescriptor.FilterDescriptors.Add(groupFilter1); queryDescriptor.FilterDescriptors.Add(groupFilter2); // paging // get the record 6 - 10 queryDescriptor.PageDescriptor.PageSize = 5; queryDescriptor.PageDescriptor.PageIndex = 1; // sorting // sort by category ascending then by product id descending queryDescriptor.SortDescriptors.Add( new SortDescriptor() { PropertyName = "CategoryID", Direction = System.ComponentModel.ListSortDirection.Ascending } ); queryDescriptor.SortDescriptors.Add( new SortDescriptor() { PropertyName = "ProductID", Direction = System.ComponentModel.ListSortDirection.Descending } );

CS

Copy Code

QueryDescriptor queryDescriptor = new QueryDescriptor();

// filtering
// get records that have
// (UnitPrice >= 0 AND UnitPrice < 50) OR (UnitPrice == 0)
CompositeFilterDescriptorCollection groupFilter1 = new CompositeFilterDescriptorCollection();

groupFilter1.LogicalOperator = FilterCompositionLogicalOperator.And;
groupFilter1.Add(
    new FilterDescriptor()
    {
        PropertyName = "UnitPrice",
        Operator = FilterOperator.IsGreaterThanOrEqualTo, Value = 0
    }
);
groupFilter1.Add(
    new FilterDescriptor()
    {
        PropertyName = "UnitPrice",
        Operator = FilterOperator.IsLessThan, Value = 50
    }
);

CompositeFilterDescriptorCollection groupFilter2 = new CompositeFilterDescriptorCollection();

groupFilter2.LogicalOperator = FilterCompositionLogicalOperator.And;
groupFilter2.Add(
    new FilterDescriptor()
    {
        PropertyName = "UnitsInStock",
        Operator = FilterOperator.IsEqualTo, Value = 0
    }
);

queryDescriptor.FilterDescriptors.LogicalOperator = FilterCompositionLogicalOperator.Or;

queryDescriptor.FilterDescriptors.Add(groupFilter1);
queryDescriptor.FilterDescriptors.Add(groupFilter2);

// paging
// get the record 6 - 10
queryDescriptor.PageDescriptor.PageSize = 5;
queryDescriptor.PageDescriptor.PageIndex = 1;

// sorting
// sort by category ascending then by product id descending
queryDescriptor.SortDescriptors.Add(
    new SortDescriptor()
    {
        PropertyName = "CategoryID",
        Direction = System.ComponentModel.ListSortDirection.Ascending
    }
);
queryDescriptor.SortDescriptors.Add(
    new SortDescriptor()
    {
        PropertyName = "ProductID",
        Direction = System.ComponentModel.ListSortDirection.Descending
    }
);

QueryDescriptor is an intermediary object that contains the query information which you can use to process the query to a service for data retrieval. The query information is stored in three different properties as shown in the following figure.

As you can see in the above figure, there are three properties which contain specific query information.

The FilterDescriptors contains a collection of FilterDescriptor that hold filtering information.
The SortDescriptors contains a collection of SortDescriptor that hold sorting information.
The PageDescriptor contains information about data paging.

QueryDescriptor provides a QueryChanged event that will be raised when any of the descriptor properties change. The QueryChanged event serves as a centralized pipeline where you want to handle all the query changes due to the actions in data controls.

CS	Copy Code
public QueryDescriptor QueryDescriptor { get { return this._queryDescriptor; } set { if (this._queryDescriptor != value) { if (this._queryDescriptor != null) this._queryDescriptor.QueryChanged -= new System.EventHandler(OnQueryChanged); this._queryDescriptor = value; this._queryDescriptor.QueryChanged += new System.EventHandler(OnQueryChanged); this.OnPropertyChanged("QueryDescriptor"); } } } private void OnQueryChanged(object sender, System.EventArgs e) { // do data operation }

CS

Copy Code

        public QueryDescriptor QueryDescriptor
        {
            get
            {
                return this._queryDescriptor;
            }
            set
            {
                if (this._queryDescriptor != value)
                {
                    if (this._queryDescriptor != null)
                        this._queryDescriptor.QueryChanged -= new System.EventHandler(OnQueryChanged);

                    this._queryDescriptor = value;
                    this._queryDescriptor.QueryChanged += new System.EventHandler(OnQueryChanged);

                    this.OnPropertyChanged("QueryDescriptor");
                }
            }
        }

        private void OnQueryChanged(object sender, System.EventArgs e)
        {
            // do data operation
        }

The QueryDescriptor concept is specifically designed for MVVM pattern implementation which allows you to bind the QueryDescriptor to your ViewModel. You can listen to its QueryChanged event and handle the data operation based on the information stored in the QueryDescriptor.

System.Object
Intersoft.Client.Data.ComponentModel.QueryDescriptor

Target Platforms: Windows 98, Windows NT 4.0, Windows Millennium Edition, Windows 2000, Windows XP Home Edition, Windows XP Professional, Windows Server 2003 family, Windows Vista, Windows Server 2008 family

Reference

QueryDescriptor Members
Intersoft.Client.Data.ComponentModel Namespace

Object Model

Syntax

Example

Remarks

Inheritance Hierarchy

Requirements

See Also

Reference