VB.net LINQ filter on multiple columns - sql

Question

Hi please can you advise me on the best way to achieve filtering on multiple columns in LINQ
Table:
CREATE TABLE [dbo].[user] (
[id] [int] IDENTITY(1,1) NOT NULL,
[firstName] [nvarchar](50) NULL,
[surname] [nvarchar](50) NULL,
[fullAddress] [nvarchar](1050) NULL
I would normally use SQL for this
Dim firstname as string = 'bob'
Dim surname as String = 'holdness'
Dim address as String = 'blockbuster street'
Dim Stmquery as string = 'Select * from users '
if not String.isnullorEmpty(firstname) or not String.isnullorEmpty(surname) or not String.isnullorEmpty(address) then
Stmquery = Stmquery & "where"
end if
if not String.isnullorEmpty(firstname) then
Stmquery = Stmquery & " firstname = " & firstname
end if
if not String.isnullorEmpty(surname) then
Stmquery = Stmquery & " surname = " & surname
end if
if not String.isnullorEmpty(address) then
Stmquery = Stmquery & " address = " & address
end if
So basically if the string is empty it will show all records for that column
Can someone show me how to do this in LINQ
Thanks Paul

Answer 1

I assume you already have LINQ to SQL DBContext prepared, with Users table mapped.
You can easily extend your query, because it's not going to be executed against database until you call ToList(), ToArray(), First(), Last(), etc.
Dim query = dbContext.Users;
If Not String.IsNullOrEmpty(firstname) Then
query = query.Where(Function(u) u.FirstName = firstname)
End If
If Not String.IsNullOrEmpty(surname) Then
query = query.Where(Function(u) u.Surname = surname)
End If
If Not String.IsNullOrEmpty(address) Then
query = query.Where(Function(u) u.Address = address)
End If
' query execution is here, after next line '
Dim results = query.ToList()