I'm developing in MVC2 using VB.NET and MySQL and ran into a problem trying to convert a simple SQL query to LINQ. SQL Query:
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Looking at that query its easy to spot whats causing the error. Simply, the most inner query only returns 2 columns, while the query right above it is trying to SELECT 3, thus the Unknown Column Error. So why is this happening? What is wrong with my LINQ query?
I have an array of unknown (to the current method) class objects. I do know that each class has a property called "Number". I am trying to write a LINQ query where I am looking for the object with the next Number in sequence. AKA, I'm at Number 8, use a LINQ query to find the object where Number=9.
View 5 RepliesI want to create a new object of a class which is not predetermined before run-time. Something along the lines of:
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I am using MySQL ODBC 3.51 Driver to connect odbc to MySQl.But it shows the following error.
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Dim MyQuery = From c In xdoc.Descendants() _
Where c.Attribute(OriginY) IsNot Nothing _
Order By Val(c.Attribute(OriginY).Value), Val(c.Attribute(OriginX).Value) _
Select c.Attribute(UniStr)
Right above you can see my First! linq attempt! And here comes my first question.
How can i select more than one column in a linq query in vb.net?
For example... Select c.Attribute(UniStr) AND c.Attribute(OriginY)
I am using a modal form with a datagridview in order to populate textboxes on a parent form. The datagridview is bound to an anonymous type resulting from a linq query, which varies depending on the textbox control whose keypress event is called. I always want to display a key value in column 0 of the datagridview (along with a variable number of additional columns), and then use that key value once the user selects a row.
However, when setting an anonymous type from a linq query as the datasource for a datagridview control, the columns are indexed alphabetically rather than in the sequence selected in the query. This requires setting the displayindex as a workaround, and then keeping track of which column contains my key value. I read elsewhere that this was something fixed in VS2008 SP1, but I still encounter the behavior.
I have this code:
[Code]...
I am getting a syntax error for the code below.I am trying to create a user in the mysql database and add their information to a datagrid control all in one button click using two statements; one to create the actual user, and one to add the user and their additional information to a table on the database and then refresh the datasource which will display the new user's information in the datagrid control.
If anyone knows where i went wrong please feel free to critique my code and let me know; or simply offer more efficient alternatives to what im hoping to achieve.
For those of you that must know, i am running the latest version of MySql server, MySql Workbench, and Visual Basic 2010 Express on a windows 7 based laptop. I'm writing this program in VB.net.
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I have a List of Price Objects (Price contains Date, High, Low) and am trying to extract monthly averages via LINQ. I have this working in C# but we have a few legacy applications that need it in VB.Net and I can't quite seem to figure out the conversion. I've even tried breaking it into two queries to no avail.
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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())
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I have a set of LINQ queries filtering original datatable (loaded from Excel file) based on user selections in Comboboxes. Then the result is joined with Arraylist to further filter the set. Arraylist is a simple list of strings.
Query:
If (Samples.Item(0) Is Nothing) = False And Samples.Item(0) <> "All samples" Then
queryResults = From records In queryResults Join samp In Samples _
On records("SAMPNUM") Equals samp _
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I am getting this error in MySQL on search for keywords. The error: Can't find FULLTEXT index matching the column list. My Database Table is a MyISAM and my dataTypes I am searching are Text. Any Ideas why I would get the above error?
View 6 RepliesI 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
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.
I have a DataGridView that is bound to a list of objects called "BaseChange". The BaseChange objects are made up of 4 properties...
ChangeType
ChangeStatus
ChangeDescription
LastChangeDate
The datagridview has columns for all 4 values as well as a 5th (a checkbox column called "colIsSelected"). There is no problem binding the list to the grid and displaying the items. The problem is that the query that gets the selected items in the grid is giving me an implicit cast error when option strict is enabled.
This is the query...
Dim _changes As List(Of BaseChange)
_changes = (From _row As DataGridViewRow In dgvChanges.Rows() _
Where Convert.ToBoolean(_row.Cells(NAME_COLUMN_IS_SELECTED).Value) = True _
Select DirectCast(_row.DataBoundItem, BaseChange)).ToList()
...and it produces the correct results with option strict off. The implicit cast squiggle is on the "row As DataGridViewRow" code, and the full message is "Implicit conversion from 'Object' to 'System.Windows.Forms.DataGridViewRow'*".
If I exclude the "As DataGridViewRow" from the query, I get a late binding error on the _row.Cells and _row.DataBoundItem and this also fails option strict.I need this to work with Option Strict enabled, and in VB.
I have a dynamic query which returns a DataTable. This DataTable will contain a varying number of columns depending on the selection used in the query. I want an efficient way of filtering the records in the DataTable.
For Example The DataTable contains columns : A, B, C and D
I need to query this data at serveral points in my program. At some point I may need records where A=10 and C>40. At another point I may need records where A<10 and D=90 etc.etc. The selects are dymanmic, I do not now what Columns or values are needed until the code is executing.
I could simply use a DataTable Filter and build the selection string dynamically. I have no problem with this. However I was wondering if using LINQ would be more applicable. I am completely new to LINQ and would like to use it but don't know its capabilities.
(At present I am using a DataTable but in future this may change to a collection of Objects)
I'm connecting to my mysql server using ODBC in vb.net, the database is shared throughout the company because it is used in an accounting program (simply accounting), each user has their own account user/pass to login to the database. I have developped a program that uses the accounting database and combines it with other information, my problem is that at least once a day I get this error when I run my program: "(10061) ERROR [HY000] [MySQL][ODBC 3.51 Driver]Can't connect to MySQL server on"and the error persists for at least 4 hours, for some reason it starts to work again later on in the day.
View 1 RepliesI have a table adaptor that pulls from the sql database, when I edit the table adaptor query it makes this specific table adaptor not a part of the dataset. I have added a column to my database which will contain an integer, when I try to add this column to the query this error occurs, i am using the configure area of the table adaptor.
Error 'AuditProductsTableAdapter' is not a member of 'MemKingClient.MemKingDataSetTableAdapters.TableAdapterManager'.
I'm trying to check if a LINQ Entity exists in its table, but at design time I dont know what type that entity is. So I figure I'll just get the table, and try the Contains method on it. But I cant get the table in such a way that I can query it at design time.I've tried the GetTable method on the datacontext, but I dont know how to cast it to the appropriate type when using GetTable(Of). GetTable(Type) works, I just use Entity.GetType(), but then I don't know how to query the ITable thats returned.To try and cast the ITable to something useable, I created an interface(IWhatever) that could implement properties that are native to all of my entities I would encounter. [code]
View 2 RepliesI have a query from within my vb.net code which searchs for a record by date. The date being entered via the code is in format dd/mm/yyyy, i need to search in the database using yyyy/mm/dd? Ideally i thought there may just be a function within MySQL which will convert this. If not in vb.net to convert the string 01/01/2011 to 2011/01/01?
View 1 Replieson first form one textbox and one button present and in second form crystal report viewer is present in first form textbox i write query and when i click on button i want report in second for with data returned by query
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given this function:
Public Function Search(ByVal StartIndex As Integer, _
ByVal MaxResults As Integer, _
ByVal AccountNumber As String, _
ByVal LastName As String, _
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instead of what I expected:
Select count(*) from remitline where lastname = "smith"
What am I doing wrong building up the where clause? I'm using Castle ActiveRecord 2.1
if there is that much of a performance gain in running a LINQ stored procedure versus a LINQ query?
View 1 RepliesThe following code populates a second dropdown when the first dropdown changes (i.e. cascading dropdowns). However, the Ajax call isn't firing, and I can't figure out why. I'm not getting any syntax or runtime errors. When in debug mode, the GetPlans action is never being called. The inner alert is never called, but the outer one is. To make matters worse, this same setup is working elsewhere in my app! Here's all the pertinent pieces (let me know if I've left out some important details):
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I have to join two main tables, and I need to filter the results by elements in an ASP.NET web form. These filters are created on the fly so I have to use a lot of where extensions to filter the query. I want to execute the query with as optimized SQL as possible.
I am first doing a simple join between TW_Sites and TW_Investigators. Then there are two sub-tables that are involved. TW_InvestigatorToArea and TW_InvestigatorToDisease. While most of the where clauses are working fine, I have found a performance issue that won't be an issue right now, but will be an issue as the table gets bigger.
The arrays DiseaseCategories and DiseaseAreas would be the results of a CheckBoxList result.
Protected Sub LoadResults()
'Get Dictionary of Filters
Dim FilterDictionary As OrderedDictionary = Session.Item("InvestigatorFilterDictionary")
' Initialize LinqToSql
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Using Access 2003 and VB code, I have created a form with a number of labels. The labels will display an employee's names. I have named the labels name1, name2, name3...etc. Using an ADO data set and DCount I have determined the number of names in an Access table (the number of names can vary). What I want to do is for each record in succession to pick the first name and surname from the data set , combine them into a full name (this part has been successful), and then set the full name into the label caption in succession. Example: full name 1 into name1, full name 2 into name2, full name 3 into name3... until all names appear as labels on the form.
I created a counter to and a variable to increment the label number but when I address the caption property of the variable containing the new label (e.g. name1, name2..etc.) it throws an errer at runtime. Here is the code:
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Forgive my ignorance on this.I have this LINQ Query:Dim ngBikersDataContext As New CarBikeWalkDataContext
bikersList = (From c In ngBikersDataContext.Reg_Bikers _
Order By c.L_Name _
Select New Bikers() With { _
.BikerID = c.BikerID, _
.F_Name = c.F_Name, _
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with the error "Overload resolution failed because no accesible 'Select' accepts this number of arguments."
Over the "NEW" I get an error " ')'expected."
I have the code below giving me grief because it gives unknown error (0x80005000) when trying to add a user to a second group[code]...
View 5 RepliesI have a program which use an API. One of the functions of this API has threading.Once I start this function. It will continue reading data and once the data is found, it will pass me the data to a function let's say functionnd I call a delegate functionB from this functionA.And at some point this functionB throw me an error of "Collection was modified; enumeration operation might not execute.".Does anyone know what this mean?I google it and found that this error was caused by "For Each or For" loop.But in my program I don't have any for loop.
VB.Net
Public Sub ReadTag(ByVal sender As Object, ByVal e As TagReadDataEventArgs)
Try
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Dim rp As New ReportDocument
Dim myData As New MyDataSet
Dim dt As New MyDataSet.UserDataTable[code]....
When setting the datasource It comes up with an error:Unknown Database Connector Error.....Error in File C:DOCUME~1A_RAHN~1LOCALS~1Temp1Report {832105B2-2E31-4018-9761-77581CC86142}.rpt:Unknown Database Connector Error
I created that report by Crystal Reports 2008 Stand-alone IDE rather than generating it in VS2010 IDE and it is binded to that dataset dutring the crystal report wizard.
