LinqInstantFeedbackSource.DismissQueryable Event

Occurs when the LinqInstantFeedbackSource no longer needs the queryable source it used to retrieve objects from the data store.

Namespace: DevExpress.Data.Linq

Assembly: DevExpress.Data.v23.2.dll

NuGet Package: DevExpress.Data

Declaration

C#

public event EventHandler<GetQueryableEventArgs> DismissQueryable

VB.NET

Public Event DismissQueryable As EventHandler(Of GetQueryableEventArgs)

Event Data

The DismissQueryable event's data class is GetQueryableEventArgs. The following properties provide information specific to this event:

Property	Description
AreSourceRowsThreadSafe	Specifies whether elements retrieved by the LinqInstantFeedbackSource‘s queryable source are thread-safe.
KeyExpression	Gets or sets the name of the key property.
QueryableSource	Gets or sets the queryable data source.
Tag	Gets or sets an arbitrary object associated with a queryable source.

Remarks

You can access the object you have assigned to the GetQueryableEventArgs.Tag property in the LinqInstantFeedbackSource.GetQueryable event handler.

Example

This example demonstrates how to initialize a LinqInstantFeedbackSource, to retrieve data from a “Purchasing.PurchaseOrderHeader” data table (included in the AdventureWorks database shipped with MS SQL Server). The PurchaseOrderHeader persistent class is declared, and mapped to the “Purchasing.PurchaseOrderHeader” data table using the System.Data.Linq.Mapping.TableAttribute attribute. Then, a System.Data.Linq.Table<PurchaseOrderHeader> is passed to the LinqInstantFeedbackSource in the LinqInstantFeedbackSource.GetQueryable event handler.

C#

using System.ComponentModel;
using System.Data.Linq;
using System.Data.Linq.Mapping;
using DevExpress.Data.Linq;

// The class describing the "Purchasing.PurchaseOrderHeader" table 
// from the AdventureWorks SQL database
[Table(Name="Purchasing.PurchaseOrderHeader")]
public partial class PurchaseOrderHeader : INotifyPropertyChanging, INotifyPropertyChanged {
    //...
    [Column(Storage="_PurchaseOrderID", AutoSync=AutoSync.OnInsert, 
        DbType="Int NOT NULL IDENTITY", 
        IsPrimaryKey=true, IsDbGenerated=true)]
    // The property mapped to the primary key column
    public int PurchaseOrderID {
    //...
    }
    //...
}

// The class describing the AdventureWorks SQL database
[DatabaseAttribute(Name="AdventureWorks")]
public partial class AdvWorksDataContext : DataContext {
    //...
    public System.Data.Linq.Table<PurchaseOrderHeader> PurchaseOrderHeaders {
        get {
            return this.GetTable<PurchaseOrderHeader>();
        }
    }
    //...
}

public partial class Form1 : Form {
    //...
    private void Form1_Load(object sender, EventArgs e) {
        // Specify the key property of the PurchaseOrderHeader
        linqInstantFeedbackSource1.KeyExpression = "PurchaseOrderID";
        // Handle the GetQueryable event, to create a DataContext and assign a queryable source
        linqInstantFeedbackSource1.GetQueryable += linqInstantFeedbackSource1_GetQueryable;
        // Handle the DismissQueryable event, to dispose of the DataContext
        linqInstantFeedbackSource1.DismissQueryable += linqInstantFeedbackSource1_DismissQueryable;
        // Assign the created data source to an XtraGrid
        gridControl1.DataSource = linqInstantFeedbackSource1;
    }
    void linqInstantFeedbackSource1_GetQueryable(object sender, GetQueryableEventArgs e) {
        // Instantiate a new DataContext
        AdvWorksDataContext dataContext = new AdvWorksDataContext();
        // Assign a queryable source to the LinqInstantFeedbackSource
        e.QueryableSource = dataContext.PurchaseOrderHeaders;
        // Assign the DataContext to the Tag property, 
        // to dispose of it in the DismissQueryable event handler
        e.Tag = dataContext;            
    }
    void linqInstantFeedbackSource1_DismissQueryable(object sender, GetQueryableEventArgs e) {
        // Dispose of the DataContext
        ((AdvWorksDataContext)e.Tag).Dispose();         
    }
}

VB.NET

Imports System.ComponentModel
Imports System.Data.Linq
Imports System.Data.Linq.Mapping
Imports DevExpress.Data.Linq

' The class describing the "Purchasing.PurchaseOrderHeader" table 
' from the AdventureWorks SQL database
<Table(Name:="Purchasing.PurchaseOrderHeader")> _
Partial Public Class PurchaseOrderHeader
    Implements INotifyPropertyChanging, INotifyPropertyChanged
    '...
    ' The property mapped to the primary key column
    <Column(Storage:="_PurchaseOrderID", AutoSync:=AutoSync.OnInsert, _
    DbType:="Int NOT NULL IDENTITY", _
    IsPrimaryKey:=True, IsDbGenerated:=True)> _
    Public ReadOnly Property PurchaseOrderID() As Integer
    '...
    End Property
    '...
End Class

' The class describing the AdventureWorks SQL database
<DatabaseAttribute(Name:="AdventureWorks")> _
Partial Public Class AdvWorksDataContext
    Inherits DataContext
    '...
    Public ReadOnly Property PurchaseOrderHeaders() As Table(Of PurchaseOrderHeader)
        Get
            Return Me.GetTable(Of PurchaseOrderHeader)()
        End Get
    End Property
    '...
End Class

Partial Public Class Form1
    Inherits Form
    '...
    Private Sub Form1_Load(ByVal sender As Object, ByVal e As EventArgs)
        ' Specify the key property of the PurchaseOrderHeader
        linqInstantFeedbackSource1.KeyExpression = "PurchaseOrderID"
        ' Handle the GetQueryable event, to create a DataContext and assign a queryable source
        AddHandler linqInstantFeedbackSource1.GetQueryable, _
        AddressOf linqInstantFeedbackSource1_GetQueryable
        ' Handle the DismissQueryable event, to dispose of the DataContext
        AddHandler linqInstantFeedbackSource1.DismissQueryable, _
        AddressOf linqInstantFeedbackSource1_DismissQueryable
        ' Assign the created data source to an XtraGrid
        gridControl1.DataSource = linqInstantFeedbackSource1
    End Sub
    Private Sub linqInstantFeedbackSource1_GetQueryable(ByVal sender As Object, _
    ByVal e As GetQueryableEventArgs)
        ' Instantiate a new DataContext
        Dim dataContext As New AdvWorksDataContext()
        ' Assign a queryable source to the LinqInstantFeedbackSource
        e.QueryableSource = dataContext.PurchaseOrderHeaders
        ' Assign the DataContext to the Tag property, _
        ' to dispose of it in the DismissQueryable event handler
        e.Tag = dataContext
    End Sub
    Private Sub linqInstantFeedbackSource1_DismissQueryable(ByVal sender As Object, _
    ByVal e As GetQueryableEventArgs)
        ' Dispose of the DataContext
        CType(e.Tag, AdvWorksDataContext).Dispose()
    End Sub
End Class