GetQueryableEventArgs.KeyExpression Property

Gets or sets the name of the key property.

Namespace: DevExpress.Data.Linq

Assembly: DevExpress.Data.v18.2.dll

Declaration

C#

public string KeyExpression { get; set; }

VB.NET

Public Property KeyExpression As String

Property Value

Type	Description
String	A String value indicating the key property name.

Remarks

Use this property in a LinqInstantFeedbackSource.GetQueryable event handler to specify the name of the key property contained in a queryable source that is provided via the GetQueryableEventArgs.QueryableSource property. Usually, the KeyExpression property specifies the name of the property mapped to the primary key column in the database.

By default, the KeyExpression property is initialized by the LinqInstantFeedbackSource.KeyExpression property value.

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