I was experimenting with creating data services from IQueryables. Rather than use the canonical example of creating a set of 3 person objects on the fly and exposing them, I decided to create a service for my application log. (Not something I plan to expose to the web, just a learning tool ;-)).

I created a wrapper class for the System.Diagnostics.EventLogEntry class because I needed to have an ID field that could be read. Thanks to Jonathan Carter’s blog post, I knew that there was no property of the real class that would work, so I needed to create my own class with a valid field for a discoverable identity property.

Having done this, I tested my service which worked just fine:

Since I knew there are  a LOT of entries in my application log file (I don’t have a sysadmin to do that maintenance for me) I thought it would be smart to filter the entries by adding /LogEntries?$top=10 to the URI. I wasn’t sure how Vista would handle that and wasn’t shocked to see in the debugger that the filtering was going to be left up to the dataservice:

It’s definitely a huge advantage to be able to expose (or interact with) any IQueryable through Astoria, but don’t forget that it’s the database that has the query processor. In this case, I was returning 23,000 items to my service to be processed.

If I do the same filter to a service that exposed a database via an Entity Data Model, for example Northwind

http://localhost:55176/DataServices/NWDataService.svc/Categories?$top=10

the query is processed by the Entity Frawework and the filter is part of query sent to the database:

SELECT TOP (10)
[Extent1].[CategoryID] AS [CategoryID],
[Extent1].[CategoryName] AS [CategoryName],
[Extent1].[Description] AS [Description],
[Extent1].[Picture] AS [Picture]
FROM [dbo].[Categories] AS [Extent1]
ORDER BY [Extent1].[CategoryID] ASC

Only 10 items are returned for the service to process.

LINQ to SQL will do the same … i.e. create a filter query that gets sent to the database.

Yes exposing my entire un-maintained application event log is not a real-life scenario and in a real network, I might even use the nice filters that Vista provides for event logs.

But the point is just to pay attention to what you may be asking your service to do.

While this has been an unfolding process on Ruurd’s blog and on the CodePlex/EFContrib site, today marks an impressive day in the evolution of the PostSharp4EF project that Ruurd Boeke has been working on.

He has used the available interfaces for IPOCO in Entity Framework to create a tool for using Entity Framework in a way that is more affable to Domain Driven developers.

His solution enables client side classes that are not dependant on Entity Framework APIs and supports a fully disconnected tiered application – the thing we have all been struggling to achieve.

Ruurd also solved the XML Serialization problem along the way, though in the meantime, changes to WCF actually solve the problem across the board for all WCF XML Serialization, including Entity Framework objects. So I’m sure that was frustrating for him to have this announced shortly after he completed that arduous step, but think of how much you learned, Ruurd and how much respect you have earned as well! 🙂

Here is short description of the project. You can find much more on the PostSharp4EF project site under the CodePlex/EFContrib home as well as on Ruurd’s blog.

PostSharp4EF: Automatically implement IPoco This project uses PostSharp to post-compile your assemblies. When it encounters a simple attribute, it will implement everything needed to use it in EF: Typelevel attributes, EDMscalar attributes, changetracking and default values. This means there are no runtime performance penalties. See Introducing EF Contrib post for more detailed information about this project. The following supporting projects are included as well and will enable the use of full disconnected n-tier usage of your domain objects:

• Circular Serializer: enables the serialization of object graphs (including circular references) with knowledge of ‘original values’.
• Editable Business Objects: does changetracking and provides the serializer with the correct values

I’ve been fiddling some more with mashing up ADO.NET Data Services using popfly.

I started a few months ago then set it aside.

Today, I extended my mashup block which serves up data from Northwind using an ADO.NET Data Service, then hooked it up to a geocoder block to transform city/country to lat/long, then hooked that up to a virtual earth map.