Visual Studio VB - Query from datatable instead of database - sql

Question

I'm a veteran Excel VBA coder who has been thrown into the deep end on this form <> Access database project. I'm working on one part of the form where users (employees) will select the site location (84 total, but not all will show based on what team they're on) and then select the department within that site. There are 2,189 total departments, so the department list should only show those for that site.
The database that we query from and update to is on a VERY slow server, so I want to pull a whole lookup table at the beginning (restricted down to those that team works on) into a datatable, then populate the first combo box with unique sites within that datatable, then populate the second combo box with all of the departments at that site.
The datatable is more or less just | ID | Site | Department |. I can fill that datatable just fine and leave it sitting in cache. And I could loop through the datatable to populate the combo boxes, but that's slower than it can be.
So is there a way to perhaps query from that datatable to either directly populate the combo boxes, or to fill a secondary datatable then to the combo boxes? For the first box, it's finding UNIQUE sites that is the challenge. Then for the second, it's departments where the site equals the one selected in the first box.
Thanks!

Answer 1

You can use Linq to Sql as mentioned by "Andrew Morton", i have made an exemple for you :
Dim da As SqlDataAdapter = New SqlDataAdapter("select * from YourDatatable, con)
Dim dt As New Data.DataTable()
da.Fill(dt)
'You can change here your condition as you need
Dim query = (From d1In dt.AsEnumerable() _
Where d1.Field(Of Integer)("ID") = 1 And d1.Field(Of Integer)
Select d1!ID, order!Site , d1!Department ,
If query.Count > 0 Then
comboBox1 .Items .Add (query(0).Site) 'Fill your Combobox1
end if
Dim query2 = (From d2 In dt.AsEnumerable() _
Where d2.Field(Of Integer)("ID") = 2 And d2.Field(Of Integer)
Select d2!ID, order!Site , d2!Department ,
If query2.Count > 0 Then
comboBox2 .Items .Add (query2(0).Department ) 'Fill your Combobox2
end if