How to create a collection of Expression>?

Question

I have a repository with the following method:

IEnumerable<T> FindAll<TRelated>(Specification<T> specification,
                                 Expression<Func<T, TRelated>> fetchExpression);

I need to pass in more than one expression. I was thinking about changing the signature to:

IEnumerable<T> FindAll<TRelated>(Specification<T> specification, 
                                 IEnumerable<Expression<Func<T, TRelated>>> fetchExpression);

Is this possible?
How do I create an array, say, of expressions to pass into this method?

Currently I'm calling the method from my service layer like this:

var products = productRepository.FindAll(specification,p => p.Variants);

But I'd like to pass p => p.Variants and p => p.Reviews for example. And then in the repository I'd like to iterate through the expression and add them to a query.

For a bit of background on why I am doing this see Ben Foster's blog post on Eager loading with NHibernate.

I didn't know [Ben Foster](http://www.imdb.com/name/nm0004936/) was a programmer! — Shibumi, Jun 30 '11 at 20:42

score 5 · Accepted Answer · edited Mar 11 '13 at 16:52

5

You could use params to do it:

IEnumerable<T> FindAll(Specification<T> specification,
        params Expression<Func<T, object>>[] fetchExpressions)
{
    var query = GetQuery(specification);
    foreach(var fetchExpression in fetchExpressions)
    {
        query.Fetch(fetchExpression);
    }
    return query.ToList();
}

You can call this like so:

var products = productRepository.FindAll(specification,
        p => p.Variants, p => p.Reviews );

edited Mar 11 '13 at 16:52

Richard Garside

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answered Jun 30 '11 at 13:47

Chris Kooken

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1

The `params` way is great, but how do you execute the expressions when they are an `IEnumerable`? Joining the `Query()` with the fetchExpressions? – Mikael Östberg Jun 30 '11 at 13:56
1

Fixed it to use object instead of TRelated. – Richard Garside Mar 11 '13 at 16:53

score 0 · Answer 2 · answered Jun 30 '11 at 13:47

You can change your call to this:

var products = productRepository.FindAll(specification,
                                         new [] { p => p.Variants, 
                                                  p => p.Reviews });

But this will only work if the T is the same in both!

How to create a collection of Expression>?

2 Answers2