比较表达式<Func<T, bool> &gt; 在查询中布尔值

Question

How would you compare Expression<Func<T, bool>> to bool in an Entity Framework query?

Here is an example of what I am trying to do:

Expression<Func<Errand, bool>> isClosed = (x)
    => x.ClosedDate.HasValue;

bool input = false;

var model = db.Errands
    .Where(isClosed == input) // comparing to just boolean is not valid
    .ToList();

How could you achieve this?

Answer 1

One option is to create the expression dynamically with a method:

public Expression<Func<Errand, bool>> IsClosed(bool closed)
{
    return x => x.ClosedDate.HasValue == closed;
}

And use it like this:

bool input = false;

var model = db.Errands
    .Where(IsClosed(input))
    .ToList();