Date fiIter Issues in LINQ - linq

Question

I have an ASPX page that collects 5 optional search criteria from a user and returns the result in a grid. Once the criteria are collected and the view button clicked, the code behind generates the filter like we have below
// aSearchCriteria is a class that holds the criteria
...
string filter = string.Empty;
if (!string.IsNullOrEmpty(aSearchCriteria.RegistrationNumber)) filter =
"f.BusinessRegistrationNumber = '" +
aSearchCriteria.BusinessRegistrationNumber + "'";
if (aSearchCriteria.ChangedStartDate != null && aSearchCriteria.ChangedEndDate != null)
{
if (!string.IsNullOrEmpty(filter))
{
filter += " && f.ChangedDate >= '" +
aSearchCriteria.ChangedStartDate.ToShortDateString() +
"' && f.ChangedDate <= '" +
aSearchCriteria.ChangedEndDate.ToShortDateString() + "'";
}
else
{
...
}
}
...
Using (CustomerEntities db = new CustomerEntities())
{
if (!string.IsNullOrEmpty(filter))
{
filter = "f => " + filter;
**return db.Customers.Where(filter).ToList();**
}
else
...
}
...
Sample:
"filter" value: f => f.ChangedDate > '01/01/2012' && f.ChangedDate < '14/01/2012'
Anytime I execute this I get this error message:
The query syntax is not valid. Near term '>', line 6, column 5.

Answer 1

you don't want to make the filter a string. What you should do instead is apply the filtering to the IQueryable you get. Something like:
var customers = db.Customers.AsQueryable();
if (aSearchCriteria.ChangedStartDate != null && aSearchCriteria.ChangedEndDate != null)
{
customers = customers
.Where(c => c.ChangedDate >= aSearchCriteria.ChangedStartDate &&
c.ChangedDate >= aSearchCriteria.ChangedEndDate);
}
// ... apply other filters as necessary
return customers.ToList();

Answer 2

Assuming you are using ObjectQuery.Where(string)
the string predicate should look like
"it.ChangedDate > '01/01/2012' && it.ChangedDate < '14/01/2012'"
(no f=> and the alias of the table is it)
Please confirm it helped :)