How can I reuse expressions within LINQ statements?

Question

I like to reuse expressions for DRY reasons, but how do I reuse the expressions within a LINQ statement?

e.g.

I have

public static class MyExpressions {     public static Expression<Func<Product,bool>> IsAGoodProduct() {         return (p) => p.Quality>3;     } } 

And would like to use that in LINQ statements, so

  var goodProds = from p in dataContext.Products                   where ????? // how do I use IsAGoodProduct here?                   select p; 

Sure, I could use the IQueryableExtension.Where function, but that would make joins and other functions alot uglier for more complex queries.

Is this possible or is it a limitation of LINQ?

Answer 1

If you move from the LINQ syntactic sugar it is possible:

var goodProds = dataContext.Products.Where(MyExpressions.IsAGoodProduct()); 

Without it, it isn't possible.

There's nothing to stop you mixing the two styles to build a single query though.

Example:

  var goodProds = from p in dataContext.Products                                        .Where(MyExpressions.IsAGoodProduct())                   group p by p.Category into g                    select new {Category = g.Key, ProductCount = g.Group.Count()};