LINQ Query To Combo-box
Nov 19, 2010
I am trying to use a Linq Query to pull Data from a Dataset and put it into a Combobox. I am getting a Cannot Convert Type String to Boolean Error and I don't understand Why. So Far I have my Linq query pulling Data from the Dataset but I have not been able to get it into the combobox.[code]The portion of code commented out is what I tried before but to no avail. I believe that the error that is occurring, the LINQ query is pulling all the elements not just the VehicleType. I also was wondering how to use the Distinct Keyword in LINQ, from my searches it seems that it should go after my Select Statement in a new Linq, but my SQL Side says thats wrong.
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Sep 22, 2009
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.
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Jul 14, 2011
given this function:
Public Function Search(ByVal StartIndex As Integer, _
ByVal MaxResults As Integer, _
ByVal AccountNumber As String, _
ByVal LastName As String, _
[Code]....
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
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Aug 6, 2009
if there is that much of a performance gain in running a LINQ stored procedure versus a LINQ query?
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Sep 14, 2010
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
[code]....
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Mar 31, 2011
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, _
[Code]...
with the error "Overload resolution failed because no accesible 'Select' accepts this number of arguments."
Over the "NEW" I get an error " ')'expected."
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Jan 27, 2011
We are doing a query against an in-memory collection of LINQ data objects. The wrinkle is that we are ordering by a column in a related table whose records have not necessarily been loaded yet (deferred loading:)
Dim oPkgProducts = _
From b In oBillPkg.BillProducts _
Where b.Successful.GetValueOrDefault(Common.X_INDETERMINATE) = _
[code]....
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Aug 31, 2011
How do I add ROW_NUMBER to a LINQ query or Entity? How can I convert this solution to VB.NET?
[Code]...
I'm having trouble porting that last line. I have been unable to locate a VB.NET example. I'm actually not looking for any paging functionality like the example provides, just good old-fashioned Row_Number(Order By X) row index.
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Apr 16, 2011
I was wandering is it possible to use a query within another query below is the code I am trying to use.
Public Function GetInventByComp(ByVal CompID As String) Using DC As New DataClassDataContext
'need to get company id's based off names? thats bad should be name from Id need to rethink this
Dim invent = (From C In DC.Inventors_Companies _
Where C.CompID = CompID _
Select C.InventorID).ToString
[Code]...
I was trying to us multiple values in a string like "1, 3, 5" but I can't seem to get that working either so I am trying to use just a single value now. Can anyone help me? "Yes I am new to this"
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Apr 8, 2011
I'm doing a movie database project where I want to add a first name, surname, DVD and role of that person in that movie to a query which will be displayed in the next tab.
Here's a couple of screen shots of what I'm talking about.
[URL]
Here is the code I have in the submit button as seen on the first screen shot.
Private Sub Button2_Click(ByVal sender As System.Object, ByVal e As System.EventArgs) Handles Button2.Click
BindingSource4.AddNew()
[Code].....
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May 25, 2010
I have a form that queries a database into a dataset then sets textboxes to values from the query. I have a status field I want to be able to control so I created a combo box with typed in values(Active, Inactive, Missing, Broken,Calibration). The purpose of this form is to view the current information on the item and edit if need be. I want to display the current status in the combo box. I can't get the combo box to display the value from the query. How do I do that.
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May 29, 2012
PROBLEM: I want to only show specific database records based on serveral combo-box inputs from a user. I'm looking to query an Access database from within a form I've created for viewing simple Jpegs of CAD files and pointcloud data. I've never worked with table adapters, SQL statements, or much in the way of databases before and I'm lost.
Do I add a new query and do what I want from a configuration wizard somehow? That method gave me a toolstrip button with no combo-box.Should the combo-box be bound to the table or should it stand alone?Can this be done without the use of a wizard (purely in an event) I've been told what I'm looking to do is rather simple, I'm just unable to find syntax that has worked for me.
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Jun 22, 2012
I have a combo with 6 text NA,PO,FA,GO,VG,EX and I want to do a Linq query upon the selected value in this combo used as field in the where clause. for example:
'if "NA" is selected :
Dim query = from t in db.table where t.NA > 0 Select t
'If "PO" is selected :
Dim query = from t in db.table where t.PO > 0 select t
How to do this in elegant way without writing 6 if statement or using "Select case"
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Aug 2, 2010
I'm fairly new to visual basic and have a problem that is probably quite easy to solve yet I have been unable to do it so far and am about at wits end.I have an access database with a table that contains a list of cities and states. what i would like to do is to populate a combo box on a vb form with a list of the states in the states column. the query that i have is as follows:
SELECT DISTINCT State from Cities I have previewed the data in the dataset designer and it works, i just can't figure out how to make it fill the combo box. i initially created a table with just all of the states and then used a binding source and table adapter to bind it to the combo box, but if I'm able to figure this out this would help with my application going forward
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Feb 24, 2009
I'm trying to make a database program in VB 2008 and have come across a problem with a query that I'm not sure how to solve. I have a combo box which contains names of teams that are held within the database, when a team name is selected I have 4 queries that will separate players (in that team) by their position, using this information I will then be able to display information about the players in a collection objects so that it can be edited and what not.
My problem is that I need to be able to refer to the records in the query so that I can assign a players details to objects on the form, I've used a piece of code to do so that I used previously to select individual records from a table, however when I click on a team in the combo box it throws up the error: "Could not format node 'ClientQuery' for execution as SQL.". Not being a particularly experienced VB programmer this error doesn't exactly mean too much to me, although I am not exactly sure of another way to tackle the problem.
The code for this query is:
Dim GK(3, 2) As String
Dim c As Integer = 0
For Each Record In GoalkeeperQuery
[CODE]...
All the fields in the query are strings. If this is not enough information I can post the query I used to select the records in the query used above or anything else that's related.
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May 1, 2012
[Code]...
how can get the name of the table that = to the name of the combobox1 when i select it.
[Code]...
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Jun 2, 2009
I have the following query that executes when my form loads. It's the rowsource for my combo box. The query is fine and populates the combo perfect, however, when i click into the combo box I cannot click out of it or even close the form. I have tried taking out the line of code that fills the form via table adapter on load and it works fine (opening the form unbound by the main table). Has anyone run into this before? I have another combo box on the form setup the exact same way and this is not happening. I've experimented with different datatypes etc....
code to populate combo box:
Public Shared Function LoadCallSource() As String
Dim sConnectionString As String = "Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:Documents and Settingsdiw07My DocumentsDaily Backupsphone memo backend.mdb"
[code]....
If I take out the line
Me.MemoTableAdapter.Fill(Me.Table_Memo.Tables("Memo"), intMemoID)
The Combo boxes do not act up or "Lock"
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Sep 4, 2009
I've been reading a fair bit about the performance of using LINQ rather than using a for each loop and from what I understand using a LINQ query would be a little bit slower but generally worth it for convenience and expressiveness. However I am a bit confused about how much slower it is if you were to use the results of the query in a for loop.
Let's say that I have a set called 'Locations' and a set of objects called 'Items'. Each 'item' can only belong to one 'location'. I want to link items that are under the same location to each other. If I were to do this using a normal 'For Each' loop it would be something like this:
For Each it as Item in Items
If it.Location.equals(Me.Location)
Me.LinkedItems.Add(it)
End If
Next
However if i was to use LINQ it would instead be this:
For Each it as Item in Items.Where(Function(i) i.Location.equals(Me.Location))
Me.LinkedItems.Add(it)
Next
is the second (LINQ) option going to loop once through the entire 'Items' set to complete the query, then loop through the results to add them to the list, resulting in essentially two loops, or will it do the one loop like the first (For Each) option?
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Mar 24, 2012
Is it possible to do the following? [code] Basically I have one Load_Gridview function that is called on all postbacks, and rather than creating a bunch of different cases.I want the filters to stack.My actual code has more filters set up (4 or 5 of the).It all compiles ok but when I run and try to execute with active checked, or a department selected I get the following error. [code]
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May 5, 2009
I have below XML file
<?
xml version="1.0" encoding="utf-8" ?><
PageFlow>
<
attributegroup name="Search"><
attributes>
[Code]...
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Apr 18, 2012
I am looking to sum the "Status" field.
Dim _detailRecords As New DataTable
_detailRecords.Columns.Add("y")
_detailRecords.Columns.Add("z")
[Code]....
I'm also wanting to keep this as an IEnumerable of DataRow because I will be creating a datatable from it with
Dim yyyyy As DataTable = query8.CopyToDataTable
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Aug 13, 2010
I am Fairly new to Linq and I am trying to write a simple query to return the error messages within my xml file.
<?xml version="1.0" encoding="utf-8"?>
<Error xmlns="urn:xxxxx">
The following errors were detected:
[code].....
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Aug 26, 2009
if I run this under c#
from p in Addresses where p.Address2 == null select p.AddressID
it generate this query
SELECT [t0].[AddressID]
FROM [dbo].[Address] AS [t0]
WHERE [t0].[Address2] IS NULL
if I run this under vb.net
from p in Addresses where p.Address2 = nothing select p.AddressID
it generate this query
SELECT [t0].[AddressID]
FROM [dbo].[Address] AS [t0]
WHERE [t0].[Address2] = ''
p.Address2 is a varchar field that accept null value
why vb.net is "wrong" ?
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Dec 1, 2009
I'm converting the Linq query below from C# to VB.Net. Can you spot my error? The query joins 3 XML datasets. C# - This one works great.
List<Course> courses =
(from course in CourseXML.Descendants(ns + "row")
join coursecategory in CourseCategoryXML.Descendants("Table") on (string)course.Attribute("code") equals (string)coursecategory.Element("DATA")
[code]....
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Mar 14, 2011
I have been trying the following but it returns unexpected results:
Dim xd As XDocument = _
<?xml version="1.0" encoding="utf-8"?>
<root>
[code].....
The above result returns both 'element' nodes however it should only return the first where element/subelement@id=1/subsubelement@id=3 However if results.Ancestors. is used it returns the correct 'subelement' and if that line is not included it returns a single 'subsubelement' whih is also correct I don't understand why when mvoing to the 'element' it returns both (I realise both have a subelement with id=1 but I thought each further query would filter out the presvious results)?
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Feb 22, 2012
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.
[Code]...
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Jun 24, 2011
Ok im trying to do a if statement in Linq and was wondering if it was possible to do something like:
Dim loadFriends = From p In db.UserRelationships Where p.aspnet_User.UserName = User.Identity.Name _
Or p.aspnet_User1.UserName = User.Identity.Name And p.Type = 1 _
Select New With {if p.aspnet_user1.user = "a certan username" then .username = _
p.aspnet_user.username else .username = p.aspnet_user1.Username}
[Code]...
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Sep 2, 2011
Dim query = From o In myContainer.MyObjects Select o.MyStringProperty Distinct
Dim myProperties As List(Of String) = query.ToList????? 'no way!!!'
"query" type is IEnumerable(Of String)
I tried to use the query directly as a DataSource of a (infragistic) combobox, but it throws me NullReferenceException, so I decided to convert it to a listof strings, to be a more "classical" datasource.
Dim values As List(Of String) = query.AsQueryable().ToList()
does not work either: Value of type 'System.Collections.Generic.List(Of System.Linq.IQueryable(Of String))' cannot be converted to 'System.Collections.Generic.List(Of String)'.
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Sep 20, 2011
user.fld_usr_name is a string with the value random name user is an object that is given as a parameter
ByVal user As GUser
this is the linq query that doesn't work
Dim result = (From usr In users Where usr.Name.Contains(user.fld_usr_name) Select usr).ToList()
this is the one that works
Dim result = (From usr In users Where usr.Name.Contains("random name") Select usr).ToList()
this is the error
Object reference not set to an instance of an object.
I am using this in Linq to Active Directory library which probably means it's linq to entities I've tried everything?
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Sep 27, 2011
In this query against a datatable i'm trying to do some conditional filtering.The check against Timeband(index N) should only be done when the Index exists. (the base code only had three item fields, i've converted them to a simple list)
Dim res As DataTable =
(
From dr As DataRow In dtTimedRow.AsEnumerable()
Select dr
[code]....
The above code triggers an Exception if the count = 1. It executes the code next to imeBands.Count > 1 which it should not. What would be the correct solution for this code.In the mean time i've added a simple filter function.
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