PredicateBuilder Usage

Kevin Marois

I've never used PredicateBuilder before. If anyone has used it, I could use some help

List<PurchasingEntity> results = null;

IQueryable<PurchasingEntity> query = (from c in db.Companies
join p in db.Projects on c.Id equals p.CompanyId
join j in db.Jobs on p.Id equals j.ProjectId
select new PurchasingEntity
{
CompanyId = c.Id,
ProjectId = p.Id,
JobId = j.Id,
Phase = j.Phase,
Quantity = j.Quantity.HasValue ? j.Quantity.Value : 0,
StartDate = j.StartDate.HasValue ? j.StartDate : null
});

var predicate = PredicateBuilder.True<Purchasing>();

if (companyId > 0)
{
predicate = predicate.And(i => i.CompanyId == companyId);
}

if (projectId > 0)
{
predicate = predicate.And(i => i.ProjectId == projectId);
}

if (startDate != null)
{
predicate = predicate.And(i => i.StartDate >= startDate);
}

if (endDate != null)
{
predicate = predicate.And(i => i.StartDate <= endDate);
}

results = query.Where(predicate); // <===== ERROR HERE
return results.ToList();

The compilation error is

cannot convert from 'System.Linq.Expressions.Expression<System.Func<Jayhawk.DAL.DataContext.Purchasing, bool>>' to 'System.Linq.Expressions.Expression<System.Func<Jayhawk.Entities.PurchasingEntity, int, bool>>'

Not quitre sure what's wrong here? Can anyone help?

If it's not broken, fix it until it is. Everything makes sense in someone's mind. Ya can't fix stupid.

Lost User

List<PurchasingEntity> results = null;

IQueryable<PurchasingEntity> query =

var predicate = PredicateBuilder.True<Purchasing>();

results = query.Where(predicate); // <===== ERROR HERE

"(I) am amazed to see myself here rather than there ... now rather than then". ― Blaise Pascal

Mycroft Holmes

Bugger that looked really useful but it is in c#7, VS 2017. We are stuck with 2015.

Never underestimate the power of human stupidity RAH

Keviniano Gayo

It will cause an error because you are assigning IQueryable to List. You can try this:

results = query.Where(predicate).ToList(); // <===== TO LIST HERE
return results

I didn't used PredicateBuilder but i used System.Linq.Dynamic to create dynamic filtering or order by.

[Signature space for sale]

Kevin Marois

public static class PredicateBuilder
{
public static Expression<Func<T, bool>> True<T>() { return f => true; }
public static Expression<Func<T, bool>> False<T>() { return f => false; }

public static Expression<Func<T, bool>> Or<T>(this Expression<Func<T, bool>> expr1,
                                                    Expression<Func<T, bool>> expr2)
{
    var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
    return Expression.Lambda<Func<T, bool>>
            (Expression.OrElse(expr1.Body, invokedExpr), expr1.Parameters);
}

public static Expression<Func<T, bool>> And<T>(this Expression<Func<T, bool>> expr1,
                                                        Expression<Func<T, bool>> expr2)
{
    var invokedExpr = Expression.Invoke(expr2, expr1.Parameters.Cast<Expression>());
    return Expression.Lambda<Func<T, bool>>
            (Expression.AndAlso(expr1.Body, invokedExpr), expr1.Parameters);
}

}

If it's not broken, fix it until it is. Everything makes sense in someone's mind. Ya can't fix stupid.

Kevin Marois

I must have stared at that for an hour. Just didn't see it

var predicate = PredicateBuilder.True<PurchasingEntity>();
.
.
.
results = query.Where(predicate).ToList();

This works now Thanks!

If it's not broken, fix it until it is. Everything makes sense in someone's mind. Ya can't fix stupid.