Xpo on ZeroSharp

Fluent queries with DevExpress XPO - Implementation

Wed, 14 Aug 2013 11:03:00 +0100

Continuing from my last post, I’ll demonstrate how to create a fluent interface so that you can do:

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var customer = Session
 .Query()
 .InTransaction
 .Contacts
 .ByPosition("Developer")
 .ThatHave
 .NoPhoto()
 .And
 .TasksInProgress()
 .And
 .TasksWith(Priority.High) 
 .FirstOrDefault();

First, let’s look at the ‘beginning’ of the fluent interface: the Query() extension method.

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public static class QueryExtensions
{
 public static IQueries Query(this Session session)
 {
 return new Queries(session);
 }

 // If we're using XAF, do the same for ObjectSpace as well
 public static IQueries Query(this IObjectSpace objectSpace)
 {
 var xpObjectSpace = objectSpace as XPObjectSpace;
 var session = xpObjectSpace.Session;
 return new Queries(session);
 }
}

What does the Queries() class look like?

Fluent queries with DevExpress XPO - Intro

Mon, 12 Aug 2013 17:54:00 +0100

There are many ways to perform queries with XPO.

You can do this:

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 Session.FindObject<Contact>(new BinaryOperator("Name", "Elvis"));

or this

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 Session.FindObject<Contact>(CriteriaOperator.Parse("Name = 'Elvis'"));

Another way to use the simplified criteria syntax, and with the Xpo_EasyFields CodeRush plugin. Then you can do:

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Session.FindObject<Contact>(Customer.Fields.Name == "Elvis");

For each of the above, you can optionally query within the transaction by passing in the PersistentCriteriaEvaluationBehavior.InTransaction parameter.

Or we can use LINQ via XPQuery<T>.TransformExpression().

Session.FindObject<Contact>(
 XPQuery<Contact>.TransformExpression(Session, c => c.Name == "Elvis")
 );

All of these methods are powerful, but the power comes at a cost. The syntax is neither elegant nor particularly clear and as a result it is not very practical to maintain or test.

XpoBatch source code available

Wed, 25 Jul 2012 16:24:00 +0100

The source code for the fast batch operations with DevExpress XPO is now available on on GitHub.

It includes unit tests that can be run against SQL Server or in memory. It runs against DevExpress 12.1.7, but it will work against 11.2 (and possibly earlier versions) with a couple of minor modifications which are documented in the code.

References

Fast batch modifications with DevExpress XPO

Tue, 24 Jul 2012 14:02:00 +0100

Last week I wrote about fast batch deletions. In this post I’ll show how to do the same for modifications.

Let’s assume we want to replace the ‘State’ property with ‘CA’ and CostCenter with 123 for all records where the ‘City’ is ‘San Francisco’. The recommended DevExpress approach would be something like the following:

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using (UnitOfWork uow = new UnitOfWork())
{	
	var xpCollection = new XPCollection<MyObject>(uow, CriteriaOperator.Parse("City == 'San Francisco'"));
 foreach (MyObject myObject in xpCollection)
 {
 myObject.State = "CA";
 myObject.CostCenter = 123;
 }
 uow.CommitChanges();
}

The problem with the above code is that every record must be loaded and then an individual UPDATE command is generated for each modification. This is necessary for the business logic to be applied correctly (such as the code in methods such as OnSaving()). It is also necessary to handle record locking.

Fast batch deletions with DevExpress XPO

Thu, 12 Jul 2012 17:00:00 +0100

When deleting a collection of objects, DevExpress recommends using Session.Delete(ICollection objects). This has the same effect as calling the Delete() method for every object in the collection so that the business logic is applied correctly. The business logic in this context refers to code such as that in the OnDeleting(), OnDeleted() methods, but it also includes the clearing of references to the object by other objects. This approach is slow, but ensures the integrity of the data.