GetQueryableEventArgs.Tag Property

Gets or sets an arbitrary object associated with a queryable source.

Namespace: DevExpress.Data.Linq

Assembly: DevExpress.Data.v21.1.dll

Declaration

public object Tag { get; set; }

Property Value

Type Description
Object

An object associated with a queryable source.

Remarks

Use this property in a LinqInstantFeedbackSource.GetQueryable event handler to pass an arbitrary object, along with a queryable source supplied via the GetQueryableEventArgs.QueryableSource property. The object will also be passed to a LinqInstantFeedbackSource.DismissQueryable event handler, so that you can dispose of it when the queryable source is no longer required for the LinqInstantFeedbackSource. For instance, you can assign the Tag property a DataContext, instantiated within a LinqInstantFeedbackSource.GetQueryable event handler, and then dispose of the DataContext within a LinqInstantFeedbackSource.DismissQueryable event handler, as shown below.

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