Linq And Generics. Using GetValue Inside A Query?
Dec 28, 2010
I'm triying to make a function that add a 'where' clause to a query based in a property and a value. This is a very simplefied version of my function.
Private Function simplified(ByVal query As IQueryable(Of T), ByVal PValue As Long, ByVal p As PropertyInfo) As ObjectQuery(Of T)
query = query.Where(Function(c) DirectCast(p.GetValue(c, Nothing), Long) = PValue)
Dim t = query.ToList 'this line is only for testing, and here is the error raise[code].....
The error message is: LINQ to Entities does not recognize the method 'System.Object CompareObjectEqual(System.Object, System.Object, Boolean)' method, and this method cannot be translated into a store expression.Looks like a can't use GetValue inside a linq query.
Private Function simplified2(ByVal query As IQueryable(Of T))
query = From q In query
Where q.GetType.GetProperty("Id").GetValue(q, Nothing).Equals(1)[code]....
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Jul 28, 2009
I am trying to write a generic function that generates an Xelement based on a list of objects, and a property of the object[code]....
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Apr 20, 2011
I have a listbox on my xaml form that I bound to a List(Of MyType) property. I populated this list like so:
Dim fields As List(Of CheckableFields) = New List(Of CheckableFields)
Using context As ITIPEntities = New ITIPEntities()
Try[code]....
Now I'm at the point where the user selects the fields they want included in a report and I need to iterate over the required fields. This is my linq query:
For Each checkedField In _requiredFields
If checkedField.IsChecked Then
If checkedField.FieldData IsNot Nothing AndAlso checkedField.FieldData.Trim IsNot String.Empty Then[code].....
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Feb 6, 2012
I have got the list of Class Name as Follows: Type[] typelist = typeof(Sample.Students).Assembly.GetTypes();
Now i have complete list of all classes available in Sample NameSpace:
Now i want to get data through class I am using Devexpress Persistance class so basically i have to create XPQuert Object as follows: XPQuery<Employee> EmployeeQuery = new XPQuery<Employees>(XPODefault.Session);
But in my case Employee class will be listed in typelist variable..How can i create the object of XPQuery.. is it possible something like this: XPQuery<typeof(typelist[0].Name)> EMployeeQuery = new XPQuery<typeof(typelist.Name)> (XPODefault.Session);
I meant i want to create object dynamically.
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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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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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Jun 30, 2009
I'm basically brand new to LINQ. I've seen some examples that allow me to strong type objects using LINQ but I don't really understand them because they're in C#, which I guess lets you do different things with LINQ(I think?). [Code] I just want to get a list of all the products from the XML doc and put them into a Generics list.
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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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May 12, 2012
I'm trying to learn the query structure. I have the following XML:
<?xml version="1.0" encoding="utf-8"?>
<list>
<item>
<due>07 May 2012</due>
[code]....
And I'm trying to delete <item> elements with a query:
Dim DeleteItems = From e In Root.Elements("list") Where e.Element("name").Value = Text
However it isn't working. I think it's trying to select tags called <item> in the file's root, however it needs to be selecting <item> tags in the <list> element - which I don't know how to do.
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Apr 1, 2012
I have been for over one week now looking for an answer here.I am an Access Programmer for over more than 10 years now... But as limitation start to appear I move to VB.Net but now I'm encountering some troubles changing my codes from Access to VB.Net. One of them is trying to use one query inside another as I was able to do it in access just using the name of the query. Here is a bit different. I'm using the query builder so I save that query for later use. My query is:
[Code]...
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Feb 25, 2011
I am having trouble using FOR loop with array in query.What I am trying to do is for all the data pulled out of database I convert it to an array list and then string (this works fine). After that I am trying to make a FOR loop query for each of the data pulled out and this is where i am having trouble.
[Code]...
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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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Sep 4, 2009
I am using vb.net language I have a dropdownlist, which is filled by below pattern
"Smith,James" so first one is surname and second after "," is firstname
I have two textboxes for surname and firstname. Now I want to fill the textbox when dropdownlist is changed.I mean when user changes the dropdownlist the selected text in dropdown will be filled in related textboxes.so my result will be like this
surname.text = "Smith"
firstname.text = "James"
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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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