I have a simple query as below:
Dim sizings = From a In db.Sizings
Where a.Customer.ID = customer.ID
Select a
If sizings.Any Then
.....
The sizings.Any line is throwing a null reference exception. I thought I was meant to use .Any to determine if there were any rows returned?
isnothing(sizings) returns false.
Any ideas?
Edit - Resolution:
Don't use null objects in the LINQ Query!
Try checking that Customer isn't null before comparing its ID.
Dim sizings = From a In db.Sizings
Where a.Customer IsNot Nothing And a.Customer.ID = customer.ID
Select a
If sizings.Any() Then
'
End If
What about using sizings.Count() > 0
Related
I have a list of objects, with a property customerId which is a nullable System.Guid property.
I also have a list of id's of type System.Guid, I also added a Guid.Empty value to this list.
I try to do a join on both, but the objects with empty guids aren't returned.
Dim dos = (From d In documents Join c In allowedCustomers On c Equals If(d.CustomerGuid = Nothing, System.Guid.Empty, d.CustomerGuid) Select d).Skip(10 * (pageNr - 1)).Take(10).ToList
What is wrong? Is there another way to do this in a better way?
You are using d.CustomerGuid = Nothing but you have to use d.CustomerGuid Is Nothing.
Try this approach which uses the VB.NET's null-coalescing operator.
Dim query = From doc In documents
Join custID In allowedCustomers
On If(doc.CustomerGuid, Guid.Empty) Equals custID
Skip 10 * (pageNr - 1)
Take 10
Select doc
Dim docList = query.ToList()
Note that you can increase readability with multiple lines, also, VB.NET's query syntax is powerful than C#, so you can use Skip and Take in the query.
See the select below.
dim query = from a in MyContext.MyTables
Where Not a.ID = 1
Select a
I want to check if a value of a field is null. I am doing the following:
if query.count > o then
if a(0)("field") is nothing then
messagebox.show("INVALID VALUE FOR RETURNING")
end if
end if
It is generation an exepction that I can't compare the value a(0)("field").
How should I do it?
Thanks.
I am having an issue getting the results I am looking for. What I need to do is essentially:
Select count(invoicenbr) from invoicelist where invoicenbr = 'invoice'
but when I try it in linq I am not getting the correct results.
When I try to execute the linq query below, it gives me the count for the entire list, and not for the where invoicenbr = 'invoice'...
Here is my linq query that is returning the count for the entire invoiceList:
Dim test = (From invoices In invoicelist _
Where e.Row.Cells("invoicenbr").Value = invoice).count()
You have a naming issue in your code, i assume that it's responsible for your problem.
The variable in your query is invoices but later you use invoice to compare it with the cell value, so you have a different variable in scope with name invoice.
This should work:
Dim invoicenbr As String = e.Row.Cells("invoicenbr").Value
Dim duplicates = From invoice In invoicelist
Where invoice = invoicenbr
Dim duplicateCount As Int32 = duplicates.Count()
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!
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)
(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)
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
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!
How would I get something like this to work so that I can dynamically alter the where-clause in this linq to sql query?
Dim AccountID = 1234
Dim AccountList
Select Case Types
Case 1
AccountList = (from a in dc.Accounts where a.ID = AccountID)
Case 2
AccountList = (from a in dc.Accounts where a.ID = AccountID And a.ParentID = AccountID)
Case Else
AccountList = (from a in dc.Accounts)
End Select
Return From p in dc.Products where AccountList.Contains(p.Order.Transaction.AccountID)
With the above code I get this error:
Late binding operations cannot be converted to an expression tree
It sounds like you've either not got Option Strict on. Put it on, and specify the type of AccountList as IQueryable(Of Account). Then you won't be using late binding, and all should be well.