Question

please take a look at the following snippet:

public IEnumerable<T> Query(Expression<Func<T, bool>> filter)
{
    return filter != null ? this.ObjectSet.Where(filter) : null;
}

As for example:

public IQueryable<Department> Query(Expression<Func<Department, bool>> filter)
{
    return _context.Departments.Where(filter);
}

(original source: http://blogs.microsoft.co.il/blogs/gilf/archive/2010/06/21/revisiting-the-repository-and-unit-of-work-patterns-with-entity-framework.aspx)

Can anyone provide some concrete examples of how to go about actually calling the second method with an actual query?

Thanks!

Answer 1

To say get all departments with Sales over $100

var deparments = deparmentsRepository.Query(d => d.TotalSales > 100.0m);

Func and Expression> can both be declared the same way using lambda syntax.

In fact there’s an example in the article (in the last code snippet) you linked to already for this.

foreach(var department in uow.Departments.Query(d => d.Budget > 150000)) { ... }

Given that Query returns IQueryable there’s no reason you can’t build into more complex queries.

var deparments = deparmentsRepository.Query(d => d.TotalSales > 100.0m)
    .Select(d => new { ... });

Assuming Manager and Department have a foreign key you don’t need that join.

var deparments = deparmentsRepository.Query(d => d.Manager.Name.StartsWith("A"));