.net - Linq - Unexpected Uniqueness Constraint-type Behavior Occurring?
Mar 27, 2012
I have a database with a simple flyweight table referenced by another table. Let's call them, respectively, Category and Product.The Product table has several columns, one of which is a foreign key column (complete with constraint) to the CategoryID to a row of the Category table. It's simple, and I have many of them in this particular database.
I am using Linq in Visual Studio 2008 to represent this data in my application. Both tables appear as normal, and neither have anything special in their properties that would indicate the behaviour I'll describe.In the database itself, there are several Product rows which have CategoryID=1. There are two or three that have CategoryID=2. However, when the data is loaded into my application through Linq, iterating through context.Products shows that the first three have CategoryID=1, CategoryID=2 and CategoryID=3, and all the rest of the rows have CategoryID=NULL. This is not how it appears in the database. There are no other anomalies in this database.
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Feb 27, 2012
I'm having problems with the following Linq query (demandNb is a filter option, as a string):
[Code]...
My goal is to get all demands for the database if the filter fields is empty. If there is a filter, the function should return all demands that match the filter. Currently, when I try to convert the IQueryable collection to a list using .ToList(), the following error is thrown: Conversion from string "" to type 'Double' is not valid.
[Code]...
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Mar 1, 2012
I've spent quite a bit of time reading up on generics, covariance, etc., and I am failing to understand why I get the aforementioned compiler error in this type of codeLet's say I have a base "Bill" class made up of a collection of Lines..
Public Class Bill(Of L As Line)
Private _lines As List(Of L)
Public Property Lines() As List(Of L)
[code].....
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Apr 8, 2010
I have the below lines of code :I am getting the error as mentioned in the Title above.This error has come after converting a C# Code to VB.NET Code which is mentioned below:
C#:
public override IChannelListener<TChannel> BuildChannelListener<TChannel>(BindingContext context)
{
if (context == null)
[code]....
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Feb 28, 2011
I have the following two tables defined...
CREATE TABLE [LogLevel] (
[Id] int primary key
,[Name] nvarchar(50) not null
[code]....
After creating a fresh endity model, I add the two tables above. When I try to build I get the following errors...
Type argument 'Inxsol.CommandPlan.Data.Model.Log.LogLevel' does not satisfy the 'Class' constraint for type parameter 'TEntity'.
Value of type 'System.Data.Objects.DataClasses.EntityReference(Of Inxsol.CommandPlan.Data.Model.LogLevel)' cannot be converted to 'System.Data.Objects.DataClasses.EntityReference(Of Inxsol.CommandPlan.Data.Model.Log.LogLevel)'.
[code]....
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Mar 10, 2011
Just when I was thinking that I had Linq To Xml sussed I'm faced with yet another error! I think if I was to understand the linq search process in general better I might have more success, so any good links regarding that are also welcome. To my problem however; using the code below:
[Code]...
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Jul 22, 2011
I've got this Function:
Public Class QueryStringUtil
Public Shared Function GetQueryStringValue(Of T As Structure)(ByVal queryStringVariable As String) As T
Dim queryStringObject As Nullable(Of T) = Nothing
If queryStringVariable <> Nothing Then
If HttpContext.Current.Request.QueryString(queryStringVariable) IsNot Nothing Then
queryStringObject = CTypeDynamic(Of T)(queryStringVariable)
End If
End If
Return queryStringObject
End Function
End Class
When I try to call it like this:
Dim intTest As Integer = QueryStringUtil.GetQueryStringValue(Of Integer)("stuff")
Dim stringTest As String = QueryStringUtil.GetQueryStringValue(Of String)("stuff")
Dim datetimeTest As DateTime = QueryStringUtil.GetQueryStringValue(Of DateTime)("stuff")
stringTest gives me the error:
'String' does not satisfy the 'Structure' constraint for type parameter 'T'.
I want our other developers to not worry about having to convert a class to a structure or some stuff like that when they call this function. I just want them to be able to put a standard type in the (Of T) and have it work. I don't mind writing in extra calculations to achieve that. The other problem is I also need the function to be able to return an actual null value, so I kind of need the queryStringObject as Nullable(Of T). Which means I have to have T as Structure otherwise it tells me that won't work. So looks like if I change what T is I need to run some calculation to delcare the var as nullable or not.
I tried overloading this method so that one returns T and one returns Nullable(Of T) like so:
Public Shared Function GetQueryStringValue(Of T As Class)(ByVal queryStringVariable As String) As T
Public Shared Function GetQueryStringValue(Of T As Structure)(ByVal queryStringVariable As String) As Nullable(Of T)
And naturally it's telling me it can't do that since they just differ by return types. Is there anyway to overload this? I really don't want to have two functions.
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Mar 14, 2012
I've a simple class like this:
Public Class CalculationParameter{
public Long TariffId{get;set;}
}
In a workflow activity, I've an Assign like this:
(From tariffDetail In db.Context.TariffDetails
Where tariffDetial.TariffId = calculationParameter.TariffId).FirstOrDefault()
Dto is passed to Activity as an Input Argument.It raise following error and I'm wondering how to assign Id.LINQ to Entities does not recognize the method 'Int64
GetValue[Int64](System.Activities.LocationReference)' method, and this method cannot be translated into a store expression.
How can I assign the calculationParameter.TariffId to tariffDetial.TariffId?!
UPDATE:Screen shot attached shows that how I'm trying to assign calculationParameter.TariffId to tariffDetail.TariffId (car.Id = Dto.Id) and the query result should assign to CurrentTrafficDetail object.
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Mar 26, 2011
With a listbox visible, I have clicked on the windows form hoping to use the listbox.lostfocus event to let me hide the listbox - but the event does not occur. I suppose I can use the form.click event to hide the listbox, but how would I get the form to accept focus?
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Nov 15, 2011
I am getting a really bizarre error and it makes no sense at all.Basically I have a user entity which has a Password property. This property is of Type Binary, the server data type being Binary(512).I am reading this value in and converting it to a byte array. However whenever I run my code I am getting a completely unrelated error of Unable to cast object of type 'System.Guid' to type 'System.String'.This strikes me as very odd since I am not using a property or variable of type string or GUID anywhere in this procedure where it falls over.
The code is below:
Public Shared Function ValidateUser(ByVal username As String, ByVal password As String) As UserValidationMessage
Using db As New EntityMapDataContext
Dim u = From user In db.Users
Where user.Username = username
[code]....
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Mar 9, 2009
I am targetting framework 3.5 using a OneClick Deployment, code and packaging done in Visual Studio 2008 Standard Edition.I have code which works in my debug environment, and when installed on the development machine. It also works on one other machine. However, three other machines are throwing exceptions.The situation throwing the exception is that I have a serial port I am accessing, which is open, and which has been successfully opened. I then try to close the port using the following
[Code]...
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Oct 7, 2011
I have two radio button on my asp.net page, with AutoPostBack = True When I click on either of those, they each set a flag SaveData=False However, when I click on them, the page_load event occurs first, so the page_load event saves the data, then the radiobutton_OnCheckedChanged event is triggered. How can I trigger the OnCheckedChanged before the page_load event?
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Dec 1, 2010
I just got Windows 7, so I re-installed VB 2008 Express and have been met with some weird issues. One of which is when my program is running it used to break on a line where an error was occurring and tell what it was and let me fix it and continue. So I can see the error in the Immediate window but why is it not breaking on the line? It just continues loading the program. Is there a setting I'm missing?
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Mar 1, 2010
I have a list(of object) lets say ob1,ob2,ob3 that are classes I want to write a linq-querry that exstract from this list only one particolur object that is different time to time how can I write the linq querry?
dim List as new list(of Object)
list.add(ob1)
list.add(ob2)
list.add(ob3)
dim Result=(from P as ob3.gettype in list select p).tolist
but it does not work?
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Nov 12, 2009
Why did the anonymous type property "Points" still have the value "0"? [code]
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Oct 22, 2009
I'm out of my depth populating a windows form from an XML linq query (see code further down in post). The listbox is populated as intended, when a value is selected (row) I would like to populate the remaining form controls. The linq query I believe has created a new datatype "Anonymous Types". The query is only local to the load form subroutine but I'm not sure how to make it global.
When I define the query simply as an object the code in the selectedValueChanged event can't execute due to late databinding. how I can initially load the listbox from linq xml query and then populate the other controls when the value changes? Am I right in thinking even though the listbox is multi-columns (property) you can ONLY ever reference a row and NOT a column? I'm new to LINQ and Anonymous Types and the more I read the more confused I seem to get. On a less important note the order by is not functioning as intended (no errors) but data is always retrieved in xml file order and not by the node <text>. Also looked at using <text>.first to order the results without success.
[Code]...
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Feb 1, 2010
[code].....
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Jun 4, 2009
If you have custom type, and you wish to assign a List(of T) to that custom type[code]...
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Aug 28, 2009
Dim mYVariable = From C In dtXMLConverter Select C I am using the above mentioned syntax for getting the rows in the variable named "mYVariable" after issuing the from clause when I am moving my mouse cursor on the variable name, it is showing "Dim mYVariable As Object" instead of showing DataRow or something like that. I can't understand how to solve this problem.
where dtXMLConverter = DataTable
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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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Jun 21, 2011
I'm returning a list of database records;
Dim rsPublicChilds As System.Data.Linq.ISingleResult(Of spGetPublicObjectsResult) = Nothing
rsPublicChilds = dc.spGetPublicObject(slintLoginID, lintLanguageID, lintObjectID, lintObjectTypeID, lstrSEOURL, lstrValid)
I get an enumerable list of rsPublicChildObjects that I then convert to an array;
Dim larr_PublicChild As IEnumerable(Of spGetPublicObjectsResult) = rsPublicChilds.toArray()
That then gives me easy access to an array of the objects, so I can then do;
larr_publicchild(0).colMyValue
etc.etc
I'd like to get the minimum value of colMyValue (or any other property of the object that's been created for me) but I can't quite see how to get there.
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Feb 25, 2010
I'm trying to write a linq to object query in vb.net, here is the c# version of what I'm trying to achieve (I'm running this in linqpad):
void Main()
{
var items = GetArray(
[code].....
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Jan 5, 2012
I am using linq to fill a gridview with the information from an xml from code behind. I would like to order my Grid according to one of my elements in the xml ("value element").
gvResourceEditor.DataSource = (From resElem In resourceElements.Elements("data") _
Select New With { _
.Key = resElem.Attribute("name").Value, _
.Value = HttpUtility.HtmlEncode(resElem.Element("value").Value), _
.Comment = If(resElem.Element("comment") IsNot Nothing, HttpUtility.HtmlEncode(resElem.Element("comment").Value), String.Empty) _
}).OrderBy(?????)
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Oct 15, 2010
I have a method, that returns a group of accounts
Public Shared Function GetAllNotesByUser(ByVal UserID As Guid) As Account (??)
Using db As New MyEntity
Dim query= (From A In db.Account _
[Code].....
I would then like to pass this to another function to calculate the totals for all the accounts in the collection. Is it best practice to return an Ienumerable, a generic list, I'm just not sure what works best with LINQ and the entity framework.
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Jul 9, 2009
I'm a Linq noobie, maybe someone can point me in the right direction. What's wrong here? These anonymous types seem to have the same signatures.
[Code]...
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Sep 23, 2009
An old Yet Another Language Geek blog post explaining monads describes adding a SelectMany extension method to C# in order to extend the linq syntax to new types.I've tried it in C# and it works. I did a straight conversion to VB.net and it doesn't work. Does anyone know if VB.net supports this feature or how to use it?
Here is the C# code which works:
class Identity<T> {
public readonly T Value;
public Identity(T value) { this.Value = value; }
}
[code]....
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Mar 6, 2011
I am trying to write a LINQ equivalent of
SELECT C1, C2, C3
FROM T1
WHERE T1.C4='xyz' AND
EXISTS (SELECT 1 FROM T2
WHERE T1.C17 = T2.C24)
ORDER BY C3
I'm using EF CTP 5, so I have a DBContext variable named dbc, which includes DBSet objects T1s and T2s, based on POCOs T1 and T2.
In LINQ I write
DIM IND = From i In dbc.T1s
Where i.C4 = "xyz"
And (From t In dbc.T2s Where i.C17 = t.C24).Any
Select i.C1, i.C2, i.C3
Order By C3
Running the query I get the error message "Unable to create a constant value of type 'T2'. Only primitive types ('such as Int32, String, and Guid') are supported in this context." When I omit the inner expression (third line in the LINQ code), the query runs fine. I tried switching the orders of the inner comparison, to be t.C24 = i.C17, with no effect.
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Jul 3, 2010
I am using VB .Net for this, so I don't have access to var or this would be a simple matter.Right now my query is as follows
[code]...
So I used this query in LinqPad to help me determine what the object would look like. I got back a IOrderQueryable(Of RSError) which then contained a IGrouping(Of String, RSError) for each grouped collection of objects returned by the query.However I ended up with the current object type of errors as IOrderedQueryable(Of IGrouping(Of String, RSError)) because of the cast error I am getting in VS.
[code]...
I'm not sure how to get rid of the VB$AnonymousType_1 Part of the returned object.Am I even on the right track here or am I missing something completely?
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Nov 8, 2010
OK I have a base query that is returning a list (ObjectQuery, actually but I don't think it matters) I have about 5 subtypes based on the main type and I need to filter them. Everything works fine until I want the results to be of the main type (not a subclass) Basically I have a query that includes everything, then I filter out the types that are not checked in a checkedbox list. (asp.net) Lets say I have an Entity named Task, and SubTask1 and SubTask2 that inherit from Task
[Code]...
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Oct 5, 2010
I have a collection as follows
Private _bankRates As Dictionary(Of RateSourceBank.Key, RateSourceBank)
Where RateSourceBank.Key is simply
Public Class Key
Public RateType As String
Public EffectiveDate As DateTime
[Code].....
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