Session.FindObjectAsync<ClassType>(CriteriaOperator, CancellationToken) Method

Asynchronously searches for the first object that matches the specified criteria. This object’s type is designated by the specified generic parameter.

Namespace: DevExpress.Xpo

Assembly: DevExpress.Xpo.v19.2.dll

Declaration

C#

public Task<ClassType> FindObjectAsync<ClassType>(
    CriteriaOperator criteria,
    CancellationToken cancellationToken = default(CancellationToken)
)

VB.NET

Public Function FindObjectAsync(Of ClassType)(
    criteria As CriteriaOperator,
    cancellationToken As CancellationToken = Nothing
) As Task(Of ClassType)

Parameters

Name	Type	Description
criteria	CriteriaOperator	A CriteriaOperator descendant which represents the criteria the persistent object must match.

Optional Parameters

Name	Type	Default	Description
cancellationToken	CancellationToken	*null*	A CancellationToken object that delivers a cancellation notice to the running operation.

Type Parameters

Name
ClassType

Returns

Type	Description
Task<ClassType>	A Task that returns an object. This object represents the first persistent object that matches the specified criteria. null (Nothing in Visual Basic) if no persistent object is found that matches the criteria.

Remarks

Below is an example of using the FindObjectAsync<ClassType> method. Here, session is the Session instance.

C#

using System.Threading;
using DevExpress.Data.Filtering;
using DevExpress.Xpo;
// ...
CancellationTokenSource source = new CancellationTokenSource();
CancellationToken cancellationToken = source.Token;
Person personToUpdate = 
    await session.FindObjectAsync<Person>(CriteriaOperator.Parse("Name='Michael Suyama'"), cancellationToken);
if(personToUpdate != null) {
    personToUpdate.Birthday = new DateTime(1986, 10, 31);
    session.Save(personToUpdate);
}

VB.NET

Imports System.Threading
Imports DevExpress.Data.Filtering
Imports DevExpress.Xpo
' ...
Private source As New CancellationTokenSource()
Private cancellationToken As CancellationToken = source.Token
Dim personToUpdate As Person = _
    Await session.FindObjectAsync(Of Person)(CriteriaOperator.Parse("Name='Michael Suyama'"), cancellationToken)
If personToUpdate IsNot Nothing Then
    personToUpdate.Birthday = New Date(1986, 10, 31)
    session.Save(personToUpdate)
End If

Criteria are evaluated on the data store side. Objects created within a transaction (Cache) are not processed by the criteria. Objects modified within a transaction are not processed. Instead, their images, stored in the data store, are processed by the criteria.

To specify how filter criteria are evaluated within a transaction, use the overloaded FindObjectAsync method that takes the PersistentCriteriaEvaluationBehavior value as a parameter.

Persistent objects that are marked as deleted in the database (see Deferred and Immediate Object Deletion) are not included in the search.