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Eager query?
f#

Hi all,

I am developing an ASP.NET MVC app, usig Entity Framework in which Razor isn't showing some related values of a class (it shows the displayed class ok, but doesn't seem to traverse to the data of the relationship held with another class). After some research this may be due to a laz evaluation problem. So, is there any way to make an F# query eager?

Here is the model I try to display:

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namespace MyApp.Models

open System
open System.ComponentModel.DataAnnotations
open System.Collections.Generic

type Product() = 
    [<Key>] member val Id = Guid.NewGuid() with get, set
    [<Required>] member val Name = "" with get, set
    member val Iban = "" with get, set
    //Precio -> ONLY for Item (ConcreteProduct)
    //Marca
    member val public Brand = new Brand() with get, set  
    //Edad recomendada
    //member val RecommendedAge = "" with get, set
    //Categorías
    member val public Categories = new List<ProductCategory>() with get, set

And here is the generic query, where the DbContext is passed:

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    let getAll () =
        fun s -> query { for x in s do
                         select x }

The Id, Name and Iban are displayed correctly, but not the attributes from Brand or Categories.

Thanks a lot!

.

Hi Jacobo,

It seems to me your problem has more to do with Entity Framework than F# and perhaps you'd be able to have a quicker solution through an EF forum.

Typical ORM will have lazy loading on collection properties. This is to ensure you do not pull the entire object graph from the database when you want a single entity. This is sometimes implemented by having a proxy class (automatically by the framework) that derives from your Product class and will automatically go to the database only once you access the property.

I do not know the details of Entity Framework as I am only familiar with NHibernate and LinqToSQL, but another possibility could be that your schema or wiring isn't done properly and your Categories property will therefore not load anything.

Good luck.

By on 3/28/2013 5:02 AM ()

This may not necessarily be an answer to your question, but you can always make a lazy sequence or query eager by evaluating it, e.g. either by converting the result to a non-lazy data structure like a list, or by calling the equivalent of .Count() on it.

By on 3/23/2013 1:08 PM ()

Hi Adam and thanks for helping,

Is what you say true for related entities? From my repository I receive a structure of type 'Product list'. On the code of my controller I've tried several things to force the list to what you said: converting it toSeq, toArray, creating a dummy value resulting from products.Length and then returning products (which is the value containing the collection from the repository). Nothing seems to work except explicitly doing the query in the repository with the Include methods in it to force the loading of those related entities.

Any guess what may I be doing wrong?

Thank you very much!

By on 3/24/2013 10:34 AM ()

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