Can PredicateBuilder generate predicates that span multiple tables?

Question

I would like to dynamically generate predicates that span multiple tables across a Join in a Linq statement. In the following code snippet, I want to use PredicateBuilder o

Answer 1

I think your problem is with the type T of your PredicateBuilder - half of your predicate if acting on a Foo, the other half is on a Bar.

You could replace this with a simple manually constructed query:

void Test()
{
    IQueryable<Foo> fooQuery = null;    // Stubbed out
    IQueryable<Bar> barQuery = null;    // Stubbed out

    IQueryable<Foo> query =
        from foo in fooQuery
        join bar in barQuery on foo.FooId equals bar.FooId
        select new {Foo = foo, Bar = bar};

    if (searchName) 
    {
        query = query.Where(fb => fb.Foo.Name == "fooname");
    }
    if (searchDescription)
    {
        query = query.Where(fb => fb.Bar.Description == "barstring");
    }

    // use query here
}

An alternative method is to use PredicateBuilder but to make it work on the Foo,Bar couple - e.g.

class FooBar
{
   public Foo Foo {get;set;}
   public Bar Bar {get;set;}
}

void Test(bool searchName, bool searchDescription)
{
    IQueryable<Foo> fooQuery = null;    // Stubbed out
    IQueryable<Bar> barQuery = null;    // Stubbed out

    var query =
        from foo in fooQuery
        join bar in barQuery on foo.FooId equals bar.FooId
        select new FooBar
        {
           Foo = foo, 
           Bar = bar
        };

    var predicate = PredicateBuilder.False<FooBar>();
    if (searchName)
    {
        predicate = predicate.Or(foobar => foobar.Foo.Name == "fooname");
    }
    if (searchDescription)
    {
        predicate = predicate.Or(foobar => foobar.Bar.Description == "barstring");
    }
    query = query.Where(predicate);

    // use query here
}