Exception When Building LINQ Query With Multiple Levels Of Delegates Or Lambdas ("Value Cannot Be Null. Parameter Name: Instance")?
Jun 22, 2011
've got a function that takes two parameters (a delegate and an integer) and then creates a LINQ MethodCallExpression, which it uses to gets the results:
Public Delegate Function CompareTwoIntegerFunction(ByVal i1 As Integer, ByVal i2 As Integer) As Boolean
Public Function Test(ByVal pFunc As CompareTwoIntegerFunction, ByVal i1 As Integer, ByVal
I need to build a dynamic linq query with or operators. I have seen PredicateBuilder but that is in C# and my project is in VB. Basically I need to build a WHERE clause similar to this:
Where((this = 1 AND that = 2) OR (this = 1 AND that = 4) OR (this = 2 AND that = 4))
but the problem is the number will have to be determined dynamically at runtime, and added using a loop, like
for each item in myItems query = query.OR (this = item.a AND this = item.b) next
I am creating a mediaplayer / playlist creator tool that basically imports MP3 songs into playlists (grids). I'm looking to add search functionality where the user can search all open playlists (or a subset of the open playlists). A Playlist is basically a collection of AudioFiles, where an AudioFile is a class that holds the filename of the MP3 file and then exposes the tags (Title, Artist, Album, etc) in public properties.
The idea is that the user can search for a certain expression (for example "the"), and that he can then choose whether to search in the title, in the title and artist, in the title or artist, in the title, artist and/or album, etc. However, I'm having a hard time implementing this and also having it kind of dynamic.
At the moment I am simply gathering all the AudioFiles from the open playlists (or from the subset of playlists the user chooses) and then running a simple LINQ query to find those AudioFiles where the Title contains the search text. Then I display the resulting AudioFiles in a new playlist window:
[Code]....
In case the AND / OR distinguishing is too hard, I would be happy to start with just letting it default to 'OR', so that the user can check Title and Album for example. If he would then search for 'a' then all songs that contain 'a' in their title as well as all songs that contain 'a' in their album should be returned. I guess that makes it easier, but I still wouldn't know how to dynamically create the LINQ query.
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.
Edit - Resolution:Don't use null objects in the LINQ Query!
From r In ReceiptLines Where r.RECEIPT.RECEIPTDATE >= _reportStartDate And r.RECEIPT.RECEIPTDATE <= _reportEndDate
[Code].....
I am fetching all departments and their sales, average, count from the ReceiptLine, Receipt, ReceiptDiscount tables. The problem i am facing is, if i remove where discount > 0, I am getting null exception. But if I include that, then I only get sales that has discount. How would I write query that bring all sales less discount (if it has one).
Following is the code I get to achieve a list of Courses:
Dim Result As New List(Of WorkMateLib.CourseNameSpace.CoursesLib.Course) For Each cat As WorkMateLib.CourseNameSpace.CoursesLib.Category In Courses.CoursesOfferedMAIN.Values For Each c As WorkMateLib.CourseNameSpace.CoursesLib.Course In cat.Courses.Values Result.Add(c) Next Next
and it is working fine. However I am trying to attempt to do the same with linq and the code is:
Result.AddRange(From k As WorkMateLib.CourseNameSpace.CoursesLib.Category In Courses.CoursesOfferedMAIN.Values Where Not k.CategoryName = "" Select k.Courses.Values.ToList())
I am working on a project which feature many report files and when i click on them within VS 2010 to view them I am prompted the following error message "Value cannot be null. Parameter name: instance". instead of taking into the visual reprot designer. I can also provided the code for the file generating the error within the screen shot if needed.
I have a query that can be summarised in SQL as follows;
Select S.StockCode From StockToCheck As S
[Code]....
Where the S var is a list of strings. This gives the error 'S' is not declared and points to the S in the function call / join (GetPOSStock). So it does not seem possible to do this in Linq, can anyone confirm?
I'd like to take all suggestion either in C# or VB.NET.I have a DB diagram like the image below. I also include the database script here [URL]In the Students table, CountryId and RoomId column are allowed null. Because some records do not have info about room and country yet.Also, some students do not have essays.I'm doing a joint query with all tables. I want to select all students to project the result like this:Wanted query result.
Here's my current query that gives the result like the image below:
Dim db As New DBDataContext Dim query = From st In db.Students _ Join c In db.Countries On c.Id Equals st.Id _ Join r In db.Rooms On r.Id Equals st.RoomId _
[code].....
current query result I got only one result back because I have (2) William NoMan record in every table. But I don't get anything about others, like (3) Sync Master who has everything but RoomId.What do I need to modify the query above so it will give me all students like in the wanted query image above?
I have a VB .Net linq query that I want to return values from two tables. I currently have this: Dim query = (From c In db.Client _ Join u In db.Users _ On u.UserID Equals c.UserID _ Where (c.ClientID = 1) Select c, u).ToList query (System.Collections.Generic.List(Of )) returns several rows as expected each item containing a c and a u. How do I iterate through the queries collection?
My LINQ query contains the following Group By statement:
Group p By Key = New With { _ .Latitude = p.Address.GeoLocations.FirstOrDefault(Function(g) New String() {"ADDRESS", "POINT"}.Contains(g.Granularity)).Latitude, _ .Longitude = p.Address.GeoLocations.FirstOrDefault(Function(g) New String() {"ADDRESS", "POINT"}.Contains(g.Granularity)).Longitude}
The query works, but here is the SQL that the clause above produces
SELECT [t6].[Latitude] FROM ( SELECT TOP (1) [t5].[Latitude]
[Code]....
but this produced an error: "A group by expression can only contain non-constant scalars that are comparable by the server."
I have a method in a webservice that has parameter with which users can decide how they want to order their results. This is a List(Of String) with the names of the fields in the order they want to sort them. I know I can normally order on multiple columns by doing the following
Dim test = Bars.OrderBy(Function(x) x.Foo) _ .ThenBy(Function(x) x.Bar) _ .ThenBy(Function(x) x.Test)
However in this case this won't work since I can't chain the ThenBy function because I'm adding the sorting orders in a loop. To use ThenBy I need an IOrderedQueryable collection. This is how I would want it to work
Dim sortColumns = {"Foo", "Bar", "Test"} Dim query = From b in Bars For each column in sortColumns Select Case column Case "Foo" query = query.Orderby(Function(x) x.Foo) [Code] .....
I have a requirement to create a multi level treeview in ASP.Net (with VB) but I am completely stuck on how to start this. Currently my treeview is a fixed 2 level approach but now I need to rewrite this to be more dynamic and support extra levels being added into our database tables.So this treeview needs to support as many levels as needed without having to rewrite any code each time we want to add new level, Ideally we will just insert the data at the database level.I think I have the database part designed correctly, I created 2 tables Menu and MenuItemsMenu has 2 columns ItemID and ChildIDMenuItems has 2 columns ItemID and Description Doing this query:
I am working on a multiple choice quiz, admin screen, student login screen where they choose their level of difficulty. I have been able to start the quiz, have the questions and answers filled, user answers question, check if correct or not, if correct then the score is incremented.I am able to set up a variable for 'level' and want to write some code so that whatever is selected then that table / questions will be selected and displayed to the user.
The way I'm thinking at the moment seems very long winded. I think I'll have to write an IF ELSE statement/case statement for each of the 'navigaterecords' and the sql statment for beginners, intermediate and advanced.Assume there is a variable 'LEVEL' - have not actually done this yet. Where the code refers to 'advanced' is where I have been trying it out to select questions from the advanced table.
Private _PurchaseDelivery as PurchaseDelivery Protected Overrides Sub InsertItem(ByVal index As Integer, ByVal item As PurchaseDeliveryItem)
[Code]....
Which is inside a class which overrides a custom list base. The code is occassionaly throwing an unhandled exception, System.NullReferenceException, on this line when used in production:
If _PurchaseDelivery IsNot Nothing AndAlso _PurchaseDelivery.DefaultSKUBinID.HasValue Then
DeafultSKUBinID is declared as an Integer? (Nullable Int) in the PurchaseDelivery class. I cannot see what might be causing this error, why would this be returning an error?
When I put a break point to the last if clause in the sub ("If (backOrder < 0) Then", see below) it runs until the break point, if I put the break point further below, I get the following error:
Cannot insert the value NULL into column 'OrderID', table 'WHM.dbo.OrderDetails'; column does not allow nulls. INSERT fails. The statement has been terminated.
I've discovered first hand that it only happens when prodqty is bigger then qtyOnStock, thus executing the if clause.
The code:
Private Sub NCOSubmit_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles NCOSubmit.Click Dim sqlText As String = ""
is there a way to create an interface of delegates? Sub dostuff(byval arg1 as dele1)works, problem is that i have 8 delegates, so i will have to give it 8 signatures. that isn't so bad, but the problem is that when there are various combinations of signatures it gets real real bad.
Sub dostuff(byval arg1 as [Delegate])works, but it allows me to accept delegates beyond the 8 that i wanted (it's like declarign arguments with base Object)could i be able to do this:
I know that LINQ queries are deferred and only executed when the query is enumerated, but I'm having trouble figuring out exactly when that happens.Certainly in a For Each loop, the query would be enumerated.What's the rule of thumb to follow? I don't want to accidentally enumerate over my query twice if it's a huge result.
For example, does System.Linq.Enumerable.First enumerate over the whole query? I ask for performance reasons. I want to pass a LINQ result set to an ASP.NET MVC view, and I also want to pass the First element separately. Enumerating over the results twice would be painful.It would be great to turn on some kind of flag that alerts me each time a LINQ query is enumerated. That way I could catch scenarios when I accidentally enumerate twice.
There's a table Category with a pk idCategory and a self-referencing foreign-key fiCategory.That means categories are "main-categories" when fiCategory is null. If fiCategory links to another category, it is a sub-category of it. But it's also valid that this sub-category also has 1-n sub-categories(with fiCategory linking to it's idCategory).Q: How can i get a list of main-categories,sub-categories,"sub-sub-categories", ...etc. with LINQ?I'm using typed DataSets to compare data from Server1/MySQL with data from Server2/MS SQL-Server.After normalizing and cleaning(there are several inconsistencies) i want to import the new data into SQL-Server. First of all i have to import the main-categories, then the sub-categories and so on. Otherwise SQL-Server would throw a constraint exception when i would try to insert a row with a foreign-key to a category that is yet not inserted.
I am building a module using linq to SQL and I am running into some problems. I have been following Michal Washington's tutorial on [URL]. The problem is that VB does not recognize my Complaint Class when I try to create new Complaint object. why I am unable to Dim a Complaint object? Here is my code:
I am connecting to an Access database and using a parameter query with the LIKE operator to return all rows that match query. The string to search for is taken from a Textbox
sql =
"Select * FROM Allview WHERE Info Like" & "*" & CStr(TextBox1.Text) & "*" The query does not return any data in vb, but when run from access with same string, there is data returned.The connection to the database is done correctly, as I am able to return data with various other queries.
Partial code : Dim con As New OleDb.OleDbConnection[code]....
I am trying to run a query an Access db from VB. The general query which I want to run is
SELECT * FROM Patient WHERE Patient.PatientID = ? or SELECT * FROM Patient WHERE Patient.PatientLname = ?
I tried using an input box which captured the user input and pass that variable to the query, but that failed. Then I read about writing a function and using that, however, I keep getting an error which says Function not defined, but when stepping through the code, it seems to work. Here is my function: [Code]
I am working on a program. I created a database and used it to create a dataGridView in my program. I clicked the table adapter for the program and tried to create a new query. When I did this, I got the following error messages...Error message-the new command text returns data with schema different from schema of the main query check your query's command text if this is not desired Schema returned by the new query differs from the base query I cannot create a query for the database. What is a base query and what can I do to fix this?
I'm using the code below to search in XML files depending on the values entered in the text boxes, problem is I don't know how to combine the search statement with an "AND" when the users enter data in both textboxes. Can you please help me solve this problem? I am using VB.NET (VS 2008). Error "column can't be found is on line "Dim DV As New DataView(dt, "Receiver like " & "'" & C1TrueDBGrid1Donor.Columns(1).Value & "'" & "", Nothing, DataViewRowState.CurrentRows)"
I am trying to create a treeview in VB.net, the data has to be loaded from MSAccess 2010 database. When I try to run this program I get error : Argument Null Exception was unhandled, 'column' argument cannot be null and the program crashes. I have pasted the code as under:
Imports System.Data.OleDb Public Class frmRating Private Sub frmRating_Load(ByVal sender As Object, ByVal e As System.EventArgs) Handles
I am getting an error when I write a value to the database. it tells me "Key cannot be null. Parameter name: key". However the key is an auto-increment value and i'm not even writing to that field. I have verified that there is a value being sent to the SQL. I also created a seperate program that writes the same SQL statement to the db and it writes just fine. I also have other places within the same program that write to the database without any problems.[code]
