LinqInstantFeedbackSource.GetQueryable Event
Occurs when the LinqInstantFeedbackSource needs a queryable source, to retrieve objects from the data store.
Namespace: DevExpress.Data.Linq
Assembly: DevExpress.Data.v18.2.dll
Declaration
Event Data
The GetQueryable 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
Handle this event, to supply a queryable source connected to the required data store to the LinqInstantFeedbackSource. The GetQueryableEventArgs class exposes the GetQueryableEventArgs.Tag property, which you can use to specify an arbitrary object. This object will be passed along with the GetQueryableEventArgs.QueryableSource property to the LinqInstantFeedbackSource.DismissQueryable 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.
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();
}
}
Related GitHub Examples
The following code snippet (auto-collected from DevExpress Examples) contains a reference to the GetQueryable event.
Note
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