Stumped on Entity Framework & Lambda Expressions

Question

I know currently the compiler is not liking this statement. Getting Error

Cannot convert lambda expression to delegate type 'System.Func<MyData.Models.SomeModels,bool>' because some of the return types in the block are not implicitly convertible to the delegate return type

My Statement I'm passing to my Repository Class

var qry = repositoryClass.Find(c => c.Categories.Where(d => d.CategoryParentID == typeID));

Repository Class Find Method

        public IEnumerable<SomeModels> Find(Func<SomeModels, bool> exp)
    {
        return (from col in _db.SomeModels where exp select col);
    }

I'm not sure if this is an acceptable way of doing this so please share any better practices. I'm not the greatest at Lambda yet. — OneSmartGuy
– OneSmartGuy, Commented Jun 24, 2009 at 14:09
Re the comment - I'm not 100% sure what the model looks like, so hard to follow... but it sounds like you might want c=>c.Categories.Any(d=>...) — Marc Gravell
– Marc Gravell, Commented Jun 24, 2009 at 17:37

Marc Gravell · Accepted Answer · 2009-06-24 14:12:03Z

4

To work with EF you need an Expression<...>, applied (as a predicate) with Where:

public IEnumerable<SomeModels> Find(Expression<Func<SomeModels, bool>> exp)
{
    return _db.SomeModels.Where(exp);
}

You'd then call that as:

var qry = repositoryClass.Find(c => c.CategoryParentID == typeID);

The lambda is then translated into an Expression<...>.

If your setup is more complex, please clarify.

answered Jun 24, 2009 at 14:12

Marc Gravell

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2 Comments

OneSmartGuy Over a year ago

I am still having issues with the repositoryClass.Find(c => c.Categories.Where(d => d.CategoryParentID == typeID)); Not sure if you notice by i'm trying to get models by category. I have categoryid but trying to see if Models.Categories contains it. This is way I was trying to do a where on the category property

OneSmartGuy Over a year ago

BTW the Categories Property is a List<Categories> due to a model being listed in multiple categories.

OneSmartGuy · Accepted Answer · 2009-06-24 14:50:09Z

0

I just added a method in my Repository Class

    public IEnumerable<Models> GetByCategory(int categoryID)
    {
        var qry = _db.ModelCategories.Where(p => p.CategoryID == categoryID).First();
        qry.Models.Load();

        return qry.Models;
    }

I'm guessing because it needs to be loaded this is the best way to go.

answered Jun 24, 2009 at 14:50

OneSmartGuy

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