CODEWITHSUNDEEP
vb.netlinq
D_Bester
D_Bester

Reputation: 5911

Dynamic Where in Linq query to get all results or limit by one

I have a linq query that gets me the data I need. Then I use For Each loop to process it. 

Dim PickCustomer as string = "Some Customer"

Dim CustQuery = From Cust In myCustTable _
Select CustomerID = Cust.CustomerID, _
    CustName = Cust.Name, _
Order By CustomerID Ascending

For Each MyCust In CustQuery


Next

How can I dynamically change the query? If PickCustomer = "" then I want all the results. But if PickCustomer has a name (any length > 0) then I want to limit my linq query to only that customer. Like Where (CustName = PickCustomer)

I've been checking out dynamic Linq queries but I can't quite make it work.

Upvotes: 0

Views: 174

Answers (3)

knifebright
knifebright

Reputation: 1

Yes, I agree that there's no need to use dynamic LINQ for this. You can also try logic even outside of the query, like this:

Dim MyCompany as string = "Consolidated Messenger"

Dim companies = 
    {"Consolidated Messenger", "Alpine Ski House", "Southridge Video", "City Power & Light", 
     "Coho Winery", "Wide World Importers", "Graphic Design Institute", "Adventure Works", 
     "Humongous Insurance", "Woodgrove Bank", "Margie's Travel", "Northwind Traders", 
     "Blue Yonder Airlines", "Trey Research", "The Phone Company", 
     "Wingtip Toys", "Lucerne Publishing", "Fourth Coffee"}

If MyCompany.length = 0 then
    For Each company As String In companies
        Console.WriteLine(company)
    Next     
Else
    Dim CompanyResult = 
        From company In companies where String.IsNullOrEmpty(company) or company.ToLower() = MyCompany.ToLower() select company
    For Each comp as String in CompanyResult
        Console.WriteLine(comp)
    Next
End If

Upvotes: 0

eol
eol

Reputation: 431

I don't think you need dynamic Linq for this. Just add a where clause that deals with both cases. Something like:

Where String.IsNullOrEmpty(PickCustomer) or (CustName = PickCustomer)

Upvotes: 1

Mark
Mark

Reputation: 8160

Since LINQ queries are lazy evaluated, you can build then up in stages, so you don't really need anything dynamic in this case, just an If.

e.g. Something like this (untested):

Dim PickCustomer As String = ""

Dim CustQuery = From Cust In myCustTable
If Not String.IsNullOrWhiteSpace(PickCustomer) Then
    CustQuery = From Cust In CustQuery
                Where Cust.Name = PickCustomer
End If
CustQuery = From Cust In CustQuery
            Select
                CustomerID = Cust.CustomerID,
                CustName = Cust.Name
            Order By CustomerID Ascending

For Each MyCust In CustQuery

Next

Upvotes: 1

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