GetQueryableEventArgs.KeyExpression Property

Gets or sets the name of the key property.

Namespace: DevExpress.Data.Linq

Assembly: DevExpress.Data.v21.1.dll

Declaration

public string KeyExpression { get; set; }

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.

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();         
    }
}
See Also