DBNull When Using LINQ To DataSet

May 20, 2010

I've got the following LINQ Statement:[code]invRecord.Pack_Num is a field of type Integer. This means that when I try to access it, if it is DBNull I get a StronglyTypedException. The above code throws this exception. If, however, I remove the "invRecord.Pack_Num = PSNum" and in its place put something like "True", the code works fine. So I guess my question is, why is that that invRecord.IsPack_NumNull() returns False when the value is in fact DBNull and what can I use as a conditional instead? I've been beating my head against the wall for a while now and I can't find a solution to this problem.

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Getting Error With DBNull When Using LINQ To DataSet

Nov 12, 2011

I've got the following LINQ Statement:

[code]...


invRecord.Pack_Num is a field of type Integer. This means that when I try to access it, if it is DBNull I get a StronglyTypedException. The above code throws this exception. If, however, I remove the "invRecord.Pack_Num = PSNum" and in its place put something like "True", the code works fine. So I guess my question is, why is that that invRecord.IsPack_NumNull() returns False when the value is in fact DBNull and what can I use as a conditional instead? I've been beating my head against the wall for a while now and I can't find a solution to this problem.

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LINQ To Dataset - How To Handle DBNull

Jan 29, 2008

This is what I'm doing to select and display 3 columns of my datatable in GridView:

Dim myCustomers = From Cust In myDataset.Customers _
Select CustomerId = Cust.CustomerId, _
CustomerName = Cust.CustomerName, _
ExpiryDate = Cust.ExpiryDate
DataGridView1.DataSource = myCustomers.ToList

The expiry date has null values in many records whose expiry date is not set.On executing the query I get runtime error:System.Data.StrongTypingException "The value for column 'ExpiryDate' in table 'Customers' is DBNull."

Obviously, my LINQ query is wrong or incomplete, but I am not able to figure the way to do it correctly.

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Set A Dataset Field To DBNULL?

Oct 12, 2011

how to set a field in a dataset table back to <DBNULL>?

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.net - Filtering DBNull With LINQ?

Mar 8, 2010

Why does the following query raise the error below for a row with a NULL value for barrel when I explicitly filter out those rows in the Where clause?

Dim query = From row As dbDataSet.conformalRow In dbDataSet.Tables("conformal") _
Where Not IsDBNull(row.Cal) AndAlso tiCal_drop.Text = row.Cal _
AndAlso Not IsDBNull(row.Tran) AndAlso tiTrans_drop.Text = row.Tran _

[code]....

Run-time exception thrown : System.Data.StrongTypingException - The value for column 'barrel' in table 'conformal' is DBNull.

How should my query / condition be rewritten to work as I intended?

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Different Ways To Test DBNull From Dataset

Oct 6, 2009

Im using VB in VS 2005.I have found several methods of testing if a value from a dataset is null. Are there differences between these two ways of doing it:

[code...]

Is one faster than the other? From some searching online, there seems to be debate about the best way to handle null values.

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VS 2008 : DBNull In A Dataset.Delete Statement?

Nov 3, 2010

I am trying to work programmatically with a dataset. The tableAdapter was created by dragging and dropping the dataset on my form, and then deleting the binding navigator and dataviewgrid. The problem I am having is when I am trying to delete a record that is DBNull. The dataset.delete( ) call creates fields for each of the fields, along with their data type (say Description as String). but I get an error whenever the field has a DBNull value.

CourseTableAdapter.Delete(DBDataSet.Course.Item(1).CourseID, DBDataSet.Course.Item(1).CourseDescription)

The error is Throw New Global.System.Data.StrongTypingException("The value for column 'Description' in table 'Course' is DBNull."I do have Option Strict On, but the problem exists even if I turn it off.

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.net - LINQ Error Type DBNull Column?

Apr 29, 2011

I am querying a datagridview and it works great unless one of the cells has nothing (dbnull). How to over come this?Exceptions: Operator '=' is not defined for type 'DBNull' and type 'DBNull'.

Dim query = From row As DataGridViewRow In DataGridView1.Rows _
Where row.Cells(SelectedColumnIndex).Value = filter _
And row.Visible = False _
Select row Distinct

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.net - LINQ Replace DBNull With Blank String?

Mar 10, 2010

In this example, an error is raised if either row.FirstName or row.LastName are NULL.

How do I rewrite the Select clause, to convert a DBNull value to a blank string ""?

Dim query = From row As myDataSet.myDataRow in myDataSet.Tables("MyData") _
Select row.FirstName, row.LastName

NOTE: Since the DataSet is strongly-typed. I can use row.isFirstNameNull(), but IIF(row.isFirstNameNull(), "", row.FirstName) will not work since all parameters are referenced.

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Use LINQ Query To Convert DBNull To String?

Oct 12, 2009

I've created a small WPF app in VB9 to catalog our sizable DVD collection. This exercise has been more about learn programming than the need to have a movie database app, but I digress.The SQL database I created has a field for "Genre" that does not have an entry for all the movies in our collection. As such, when I run the method that filters the movie listing by "Genre" the compiler throws the "StrongTypingException was unhandled" error stating "The value for column 'Genre' in table 'Movies' is DBNull.".

I now understand where the DBNull problem comes from and have been searching for several hours to find a VB solution that converts the DBNull fields to strings on the fly during the LINQ query. I've found many solutions people have tried but, since I'm quite new to all this, none of them have worked for me. Pasted below is the method that throws the exception.

[Code]...

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Asp.net - Using Linq On A Dataset

May 18, 2010

I have a dataset that is populated via a SQL Stored Procedure, the format of which is below: Country | Brand | Variant | 2004 | 2005 | 2006 | 2007 | 2008 The number of rows varies between 50 and several thousand. What I'm trying to do is use Linq to interrogate the dataset (there will be several Linq queries based on user options), but a simple example would be to SUM the year columns based on Brand. I have the following that I believe creates a template for me to work with: But from here on I'm absolutely stuck!

[Code]...

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.net - GroupBy In LINQ To DataSet?

Jul 14, 2011

Background: I'm importing data from a MySQL database into a SQL-Server database(for reports and later a SSAS-Cube). I want to normalize the data at the same time. I want to group repeating Ticket_IDs to one record in a table Contact with other useful informations and leave the rawdata in the sub-table ContactDetail(with foreignkey to Contact).Hence every record in Contact has a unique Ticket_ID.

I've decided to use strong typed datasets for the import. Now i'm wondering what's the best way to detect if i've already added a Ticket_ID. I could check for it in every loop(~100000 records) but i'm assuming that there is a better/faster way.

Simplified sample-data:

Ticket_ID ID fiContact
89442226 1 1
89442226 2 1[code].....

I will have a look if this is faster than the iterating approach with a HashSet to detect if the contact was already created.

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.net - How To Work With Dataset's Datarelation In Linq

Apr 4, 2009

linq querying various nested tables in a dataset? I can't find something like that on the net.

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DB/Reporting :: Add LINQ To DataSet To Current App

Jun 4, 2012

I am using VS 2008, VB.NET and Windows XP r3.I am trying to use LINQ to DataSet in my app. In my test app, I can get it to work find. My test form has an OleDbDataAdapter, an OleDbConnection and a DataSet. It also has a DataGridView bound to the one table in the DataSet, a BindingSource and a Button.[code]

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LINQ / Select Distinct From Dataset?

Aug 20, 2010

I have a single columned datatable inside a single tabled dataset.I just want to convert this dataset to distinct rows. Here is my code, it gives compile error '.' expected.

Dim query = _
From email In ds.Tables(0) _
Select email.Field<string>("Email").Distinct()

EDIT: I changed to (Of String) and it works... BUT NOW 'query' is an ienumerable collection of characters... not a datatable... so how do I convert back easily without manually doing a loop?

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LINQ Dataset LEFT JOIN?

Jun 14, 2012

i think i have not represented my question correctly here My LEFT OUTER JOIN MSDN reference is here to visualize my problem in access databaseTABLE "T1"1234567TABLE "T2"1,sunday2,monday i need output as 1,sunday2,monday34567 i need it to done through LINQso far i did is here

Dim RIGHT_table As DataTable = ds1.Tables("t1")
Dim LEFT_table As DataTable = ds2.Tables("T2")
Dim OutPut = From LEFTsource In LEFT_table.AsEnumerable(), RIGHTsource In RIGHT_table.AsEnumerable() _

[code]...

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Linq To DataSet Order By Clause

Feb 7, 2012

I have following code that creates Linq query.
I've never used Linq until today and having problem with "Order By Clause"[code..]

If I run the code, I get following error.Name 'p' is either not declared or not in the current scope. How come p!Weight in "Select Clause" works but not in "Order By Clause"?

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Use Linq As A Data Source Instead Of Dataset?

Apr 19, 2010

I have used a datarepeater with a dataset and it was simple to implement by dragging fields from the Data Sources window onto the DataRepeater control

I am trying to use Linq as a data source instead of dataset.

How do I bind data to textbox with Linq for Datarepeater?

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Using Linq For Object Dataset Processing?

May 26, 2011

I have a collection (IList(Of Sample)) of the following class:

Public Class Sample
Public sampleNum As String
Public volume As Integer[code].....

This collection is filled from a regex that gets passed over a file.What I want to do is use Linq to generate a collection of these for each unique samplenum using the following conditions.For each samplenum: Have the highest volume where the final is greater then one

If the sample has multiple records for this volume then pick the one with the the highest final

If the previous step leaves us with no records pick the record with the highest final ignoring volume

I am extremely new to Linq and just can't get my head around this. For now I have solved this using for each's and temporary lists but I am interested in how this would be handled using pure Linq.Sample Data:

samplenum | volume | initial | final
1 | 50 | 8.47 | 6.87
1 | 300 | 8.93 | 3.15[code]......

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VB Dataset Linq With String Where Clause?

Mar 17, 2009

Right now our queries can be driven through the DataTable Select statement. However, utimately we want to end up with more complex queries. We think Linq is the answer, but can't find anyexamples of this.Here is the sysnopsis:I have a dataset containingdatatable(s) of informationI have a datatable containing business rules as strings like:

(ISNULL(MEMLNAME, '') = '')
(#1880/01/01# <= CONVERT(BIRTHDATE, 'System.DateTime') AND CONVERT(BIRTHDATE, 'System.DateTime') <= #2009/12/31#)

[code].....

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.net - LINQ Null Date Comparison In Dataset?

Aug 26, 2011

I have a DataSet where I need to filter the collection where one of the date columns is not null.

How do you term this in LINQ?

This is what I have so far but there is a compiler error on the w.CompletedDate field in the Where clause.

Dim completed = From ins In InspectionDataset.Inspection.AsEnumerable _
Where (Function(w) w.CompletedDate IsNot Nothing) _
Order By ins.Field(Of DateTime)("UpdatedDate")

I have also tried it the below way but the compiler will not allow the DBNull comparison.

Dim completed = From ins In Inspection.AsEnumerable _
Where ins.Field(Of DateTime)("CompletedDate") <> DBNull.Value _
Order By ins.Field(Of DateTime)("UpdatedDate")

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Join Multiple Datatables Using LINQ To Dataset?

Feb 8, 2012

I have been searching for quite a while about joining multiple datatables via LINQ to dataset (When i say multiple, i don't mean just 2!!!), and it seems there aren't lot of examples in the net. I have seen examples of joining two datatables, done that, no problem there. Now i want to join three datatables. And there's nothing i can find out there.For example i have a 3 datatables:

PERSON (columns: person_id, name, gender_code, ethnic_code)
GENDER (columns: gender_code, gender_description)
ETHNICITY (cols: ethnic_code, ethnic_description)

[code].....

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LINQ To DataSet - Convert EnumerableRowCollection Into DataTable

Mar 2, 2012

I am trying to convert my EnumerableRowCollection into a DataTable, but I can't see the CopyToDataTable method. The enm.CopyToDataTable() has the blue saw tooth line under it with error saying " 'CopyToDataTable' is not a member of 'System.Data.EnumerableRowCollection' ". I have set a Reference to System.Data, System.Data.Linq, and System.Data.DataSetExtensions. I thought the CopyToDataTable method was part of the System.Data.DataSetExtensions, right? Anyone know why I can't access this method?

[Code]...

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Performance Side Linq Or Dataset.Datatable?

Apr 30, 2009

from a performance point of view is it faster to work with linq to sql or dataset.datatable?

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Use Dynamic Fields Over All Of The Tables In A Dataset In LINQ?

Jan 13, 2011

How can I use dynamic fields in LINQ in the PART OF THE where query? I mean that I want to write where x = *dynamic fields* I want to do the select query in all of the tables that are in the dataset, not on one datatable.

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VS 2008 LINQ Dataset LEFT JOIN?

Jun 13, 2012

i am having 2 tables one table stores the WEEK-days another table stores the WEEK-days + other fields.i need the LINQ query to return all WEEK-days + other fields just like SQL LEFT JOIN query so far i did is [code]....

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VS 2008 Linq To DataSet Left Join?

Feb 10, 2011

The query works but only retrieve the joined rows, i want to retrieve all rows in the first datatable.My current query:

vb.net
Dim q = From regE In (From registoE In _dtRegistosAEnviar.AsEnumerable
Group registoE By colaborador = registoE.Field(Of String)("Colaborador") Into grupoE = Group
Select New With {

[code]....

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"Conversion From Type 'DBNull' To Type 'Boolean' Is Not Valid" After Checking That It's Not DBNull

Jan 18, 2012

In my ASP.Net Web-Application, I'm getting this error: Conversion from type 'DBNull' to type 'Boolean' is not valid.

[Code]...

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Can't Get Rid Of DBNULL

Dec 13, 2011

I am teaching myself vb.net with visual studio 2010 and i have ran into a wall. I have a datagrid on my form that shows all of my customers that are in the dataset that was created in access 07. I have a search bar and check boxes to select which column name to search in. Whenever I search it throws up a strong typing exception,

System.Data.StrongTypingException was unhandled by user code
Message=The value for column 'PickupTime' in table 'CustomerRouteTable' is DBNull.
Source=EXBSTESTDatabase

[Code]....

I think this means that there is nothing in the field, but this is a field that nothing should be in. If i comment the throw exception out it moves on to the next one that has nothing in the field. I tried just putting 0's in all of them but it still gives the same exception.

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DBNULL Error In .NET?

Nov 9, 2011

I am receiving this error on this line

ctl.Value = CType(Me.Value, DateTime)

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