Question

with the below, the model.Status and model.Source values may or may not be null. If null, I want the expression to pull all statuses/sources. Is this possible with lambda because the below statement is not working?

var leads = db.CallCenterLead.Include("Profile").Include("Account")
.Where(x => x.DateSent >= model.DateFrom && x.DateSent <= model.DateTo 
&& ((model.Status != null && x.Status == model.Status) || (model.Status == null)) 
&& (model.Source != null && x.Source == model.Source)).OrderByDescending(x => x.DateSent).ToList();

Answer 1

One way to do this is to use an extension method, like this:

var leads = db.CallCenterLead.Include("Profile").Include("Account")
    .Where(x => x.DateSent >= model.DateFrom && x.DateSent <= model.DateTo)
    .WhereIf(model.Status != null, x.Status == model.Status)
    .WhereIf(model.Source != null, x.Source == model.Source)
    .OrderByDescending(x => x.DateSent).ToList();

The extension method:

public static IQueryable<TSource> WhereIf<TSource>(this IQueryable<TSource> source, bool condition, Expression<Func<TSource, bool>> predicate)
{
    return condition ? source.Where(predicate) : source;
}

The method adds the predicate if the condition is true. Otherwise it just returns the source as it were.