Entity Framework 4 selective lazy loading properties

Question

Is it possible to load an entity excluding some properties? One of this entity's properties is expensive to select. I would like to lazy load this property. Is that possible?

Answer 1

I believe the default behaviour in EF is to not load relations by default. If you do load the relations then you can set

context.ContextOptions.LazyLoadingEnabled = true;

http://msdn.microsoft.com/en-us/library/bb896249.aspx

Answer 2

stimms is correct, but be careful while using lazy loading. You may have performance issues and not realize the property is getting loaded at a specific location in your code. This is because it loads the data when you use the property

I prefer to use explicit loading. This way you know when they get loaded and where. Here's a link that gives an example for the LoadProperty http://sankarsan.wordpress.com/2010/05/09/ado-net-entity-framework-data-loading-part-2/

You can also you Eager Loading by using the Include method. Example here:http://wildermuth.com/2008/12/28/Caution_when_Eager_Loading_in_the_Entity_Framework

Answer 3

With a scalar property, the only way to selectively not load a certain property is to project in ESQL or L2E:

var q = from p in Context.People
        select new
        {
            Id = p.Id,
            Name = p.Name // note no Biography
        };

+1 to Dan; doing this lazily is worse than loading it up-front. If you want to control loading, be explicit.

Answer 4

Now that you have read everyone's reply, i will give u the correct answer. EF does not support lazy loading of properties. However it does support a much powerful concept then this. Its called table splitting where you can map a table to two entities. say a product table in the the database can be mapped to product entity and ProductDetail entity. You can then move the expensive fields to the ProductDetail entity and then create a 1..1 association between prodcut and productdetail entity. You can then lazy load the productdetail association only when you need it. In my performance chapter of my book, i have a recipe called. 13-9. Moving an Expensive Property to Another Entity

Hope that helps!