LINQ to Entities .contains is ignoring results with NULL - vb.net

Question

I am new to the Entity Framework, and am struggling with what I hope is a basic problem. My code is here:
Dim accounts As List(Of STUDENT) =
(From a In SA.STUDENTs
Where (a.MATRIC_NO.Contains(matric) And a.FIRST_NAME.Contains(firstName) And a.MIDDLE_NAMES.Contains(middleName) And a.SURNAME.Contains(lastName) And a.PREFERRED_NAME.Contains(preferredName))
Select a).ToList
The query runs fine, until one of the search fields is NULL in the database. If, for instance, a matric number is entered in the seach interface but middle name is left blank, the query will not return any records if middle name is NULL in the database. If middle name is a blank space in the database then it will return the record.
Can anyone offer any pointers?
Many thanks!

Answer 1

You can add an extra check in your query. For example:
public function filterList(IEnumerable list, string name)
{
var filtered_list = list.Where(x=> x.Name.Contains(name) || string.IsNullorWhitespace(name)).ToList();
return filtered_list;
}
So you can see, if the name variable is empty, all elements will return true, so all elements will be return (no real filter applied).
So basically, you can change all filters from
something.Contains(anotherthing)
to
something.Contains(anotherthing) || string.IsnullOrWhitespace(anotherthing)

Answer 2

(From a In SA.STUDENTs
Where isnull(a.MATRIC_NO.Contains(matric) And a.FIRST_NAME.Contains(firstName) And a.MIDDLE_NAMES.Contains(middleName) And a.SURNAME.Contains(lastName) And a.PREFERRED_NAME.Contains(preferredName))
Select a).ToList
Like this `:select * from tbl where statusid = isnull(#statusid,statusid)

Answer 3

try like this ..
Dim get_rmf_2 = From rmf In t_rmf _
Where Not IsDBNull(rmf!NIVP) AndAlso rmf!NIVP = nivp_rap
this is in VB I think this is works fine

Answer 4

I managed to solve this using a different approach. If there was no value entered for a particular field, leave it out the query. I accomplished this using predicates, as below:
'create the base query
Dim accounts =
(From a In SA.STUDENTs
Select a)
'create predicates for each condition required in the query
If matric <> "" Then
accounts = accounts.Where(Function(m) m.MATRIC_NO.Contains(matric))
End If
If firstName <> "" Then
accounts = accounts.Where(Function(f) f.FIRST_NAME.Contains(firstName))
End If
If middleName <> "" Then
accounts = accounts.Where(Function(mn) mn.MIDDLE_NAMES.Contains(middleName))
End If
If lastName <> "" Then
accounts = accounts.Where(Function(l) l.SURNAME.Contains(lastName))
End If
If preferredName <> "" Then
accounts = accounts.Where(Function(p) p.PREFERRED_NAME.Contains(preferredName))
End If
'execute the query
Dim accountlist = accounts.ToList
'return the results
Return accountlist
If anyone can see anything wrong with this, or any gotchas that I'm unaware of, please let me know! I'm very new to LINQ to Entities, and LINQ in general!