LINQ Expression Starting With From And Aggregate
May 4, 2012
[code]The LINQ query going into "result" is incomplete because I'm stumped at what is happening there. I expect FirstOrDefault to refer to refer to a single Child object at that point in the expression, but it refers to a collection of child objects. Why? What is the best way to get a list of parents that have no associated child or have a child fitting a particular condition? (My actual code will have one child max, so this sample code is not representative.)I just don't understand what the collection of FirstOrDefault could be referring to. It should really be just 1 value or nothing at all times.
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May 9, 2010
1.print the cars which are fast moving cars.
i have written this code but it shows message Cannot have aggregate function in expression[code]...
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Nov 1, 2011
I want to get the average of this query.
From d In (From c In location.Descendants("temperature")
Where c.Attribute("type").Value = "hourly" Select c).Descendants("value")
Take 3
Select d
I can see the aggregate keyword in the autocomplete dropdown, but how to apply it.
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Apr 6, 2011
I've seen the operator Max used two different ways. The following two queries produce the same results. The MSIL code is slightly different. What is the benefit of using the Aggregate operator? Logically, is there a difference?
[Code]...
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Jul 1, 2009
I am working on an application in Visual Basic Express using an Access 2000 database.I am trying to get athe following SQL query to work but get an error in Access.
The query is:
SELECT [ID], [Title], [Author], [Series], [YearPublished], [ISBN], [CoverPrice], [Style], [Condition], [Signed], [Comments], Count([Title]) AS CountOfBooks, Sum([CoverPrice]) AS TotalCoverPrice
FROM tblBooks
WHERE ID=[@ID];
The error is:"You have tried to execute a query that does not include the spec ified expression 'ID' as a part of the aggragate function."
The query works fine without the 'Count' and 'CoverPrice' count and sum to the query.
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May 24, 2010
I'm having trouble getting my head around converting a traditional SQL aggregate query into a LINQ one. The basic data dump works like so:
Dim result =
(From i As Models.InvoiceDetail In Data.InvoiceDetails.GetAll
Join ih As Models.InvoiceHeader In Data.InvoiceHeaders.GetAll On i.InvoiceHeaderID Equals ih.ID
[CODE].....................
What I need to really be getting out is ih.Period (a value from 1 to 12) and a corresponding aggregate value for i.ExtendedValue. When I try to Group ih I get errors about i being out of scope/context.
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Aug 6, 2010
Given a table like
ID | Name | City
1 | X | Y
2 | Z | Y
[code].....
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Aug 3, 2011
also i have a table called Orders with several columns, they contain information about the order and store the ID of the Customer they belong to.Question is: how can i query that table with (preferably) linq (the datacontext is from LinqToSql) to return the following dataI want to search for any entry with the matching CustomerID which took place, group them by Year, Sum the Totals respectively and add them to the listview?I now i could use lamda expressions and aggregate, its just not clear how (option infer on,db is a datacontext object,CustomerID is an int32 variable):
Dim Orders = (From order In db.Orders Where order.CustomerID = CustomerID).GroupBy(Function(p) p.Date.Year).GetEnumerator
I reckon i'd have to create an anonymous type like the following:
[code].....
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Feb 21, 2011
I want to Sum of the calculated column Red which is calculated in the Function IsRed() that return an integer.When I run the query I get the following error: Method 'Int32 IsRed(Int32)' has no supported translation to SQL.How should I rewrite this to get it to work.
[Code]...
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Nov 17, 2009
convert this C# code to VB, tried couple of converters and they dont work properly.
[Code]...
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Mar 30, 2010
[QueryInterceptor("Somethings")]
public Expression<Func<Something, bool>> OnSomethings()
{
// Code here
}
I had a view guesses, looked on msdn, but there are no examples matching the way that that is used.
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Nov 18, 2010
I'm having a little trouble converting some LINQ to VB.[code]Online code translators are not helping, and my unfamiliarly with VB LINQ is not very good.
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Aug 6, 2011
THE CODE IS :
var query1 = ((from c in dt.AsEnumerable()
orderby c.Field<int>("1") descending
select c));
var query2 = (from c in query1.Take(10)
select c);
[Code]...
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Jun 9, 2010
I have the same problem as stated in this question, but the accepted solution there was a "works on my machine" answer.
[Code]...
And I receive the error: BC30201: Expression expected.
Does anyone have a more detailed idea of what could cause this?
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Dec 15, 2011
How to Join the objects in a LINQ select in this sample (C# variants accepted as well):
Class Room
Public Area As Integer
End Class
Class RoomPair
[code]....
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Mar 10, 2009
I have the following C# LINQ query expression:
[code]...
how to convert this to VB.NET?
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Oct 28, 2011
1) I am begginner to dynamic Linq and having serious trouble creating expression tree after WHERE
say.: items.Category_ID=4
I tried to construct it like: Dim products = From items In mydatacontent.Products
Dim AA As ParameterExpression = Expression.Parameter(GetType(String), "items")
Dim left1 As Expression = Expression.Property(AA, GetType(String).GetProperty("Category_ID")) here is the error Dim right1 As Expression = Expression.Constant("4") Dim BB As Expression = Expression.Equal(left1, right1)
[Code]...
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Jan 25, 2012
What I have right now is this:
Dim users = From users In tempTable _
Distinct Select users.Item("s_userid")
Dim usersCount As Integer = users.Count
But I pretty sure I shouldn't have to do that. I should be able to get the count in/from that first linq query.
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May 21, 2010
I need to test a logical expression held in a string to see if it evaluate to TRUE or FALSE.(the strig is built dynamically)For example the resulting string may contain "'dog'<'cat' OR (1>4 AND 4<6)". There are no variables in the string, it will logically evaluate. It will only contain simple operators = > < >< >= <= and AND , OR and Open and Close Brackets, string constants and numbers. (converted to correct syntax && || etc.)
I currently acheive this by creating a jscipt function and compiling it into a .dll. I then reference the .dll in my VB.NET project.
class ExpressionEvaluator
{
function Evaluate(Expression : String)
{
return eval(Expression);
}
}
Is there a simpler method using built in .NET functions or Lamdba expressions.
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Feb 3, 2011
Where can I find complex LINQ examples made using VB.NET Lambda Expression syntax?During my searches I always found 101 LINQ Samples but they use the other notation and for me is not always clear how to transform that code into a lambda expression.
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Nov 28, 2010
translation of the following C# Linq Expression (in VB.NET 2008):
syncContext.Send((obj) => eventToBeFired(this, new EventArgs()), null);
Is used in this subroutine:
private void FireEvent(EventHandler eventToBeFired)
{
if (eventToBeFired != null)
{
[code]....
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Apr 5, 2011
I know there are similar questions on stackoverflow - and I looked through them and think my issue is somewhat similar, but haven't been able to find a solution by looking at any of these other questions/answers.I'm getting the error when attempting to execute the following code:
Private Sub btnReserve_Click(ByVal sender As Object, ByVal e As System.EventArgs) Handles btnReserve.Click
' Check that the room is still available.
Dim dbCheckOccupants As New pbu_housingEntities
Dim hall As String = CStr(Session("hall"))
[code]....
It is catching an error on this line:
Dim myID As String = GetID.First.id.ToString
As far as I can tell I'm not using multiple contexts?
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Oct 2, 2009
Of the 51 Standard Query Operators (of which only 42 are actually query operators), only 24 are directly supported by Visual Basic 9 and just 11 by C# 3: Query Expression Syntax for Standard Query Operators.In many cases, query syntax is arguably more readable than the equivalent method syntax, especially when transparent identifiers are involved. However, that readability breaks down if you have to combine queries and method calls.So the question: What query operators, current or hypothetical, would you like to have your language of choice support in query expression syntax?
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Feb 3, 2011
I am trying to convert the following code for the variance calculation
public static double Variance(this IEnumerable<double> source){
double avg = source.Average();
double d = source.Aggregate(0.0,
(total, next) => total += Math.Pow(next - avg, 2));
return d / (source.Count() - 1);
}
Described on CodeProject into corresponded VB.NET lambda expression syntax, but I am stuck in the conversion of Aggregate function. How can I implement that code in VB.NET?
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Feb 25, 2011
I have a query that I cannot seem to replicate in expression method chain syntax. I have two tables "User" and "UserPayment". User and UserPayment have a one to many relation i.e. One User can have many UserPayments.
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Nov 18, 2010
I am finding this weird issue. When I do this > activities.Where(Function(a) (Not a.IsDeleted And a.ParentId = 100) It returns an in-memory query & when I try opening it up, it throws a object not set exception. This only happens when there were no items which satisfied the condition. Shouldn't it be returning an empty set? When there are items satisfying the condition, then it returns a list & works all good.
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Apr 16, 2010
I have a lambda expression that builds a list ofanonymous types. I would like to include a property in the anonymous type that is a counter. So the first entry is 1, second 2, third 3, and so on.I thought I recallenyone know the syntax for defining an indexing variable as part of a Linq query or lambda expression?
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Mar 23, 2009
I have a requirement where I have to add items into a List(Of T) (let's call it Target) from an IEnumerable(Of T) (let's call it Source) using Target.AddRange() in VB.NET.
Target.AddRange(Source.TakeWhie(Function(X, Index) ?))
The ? part is a tricky condition that is something like: As long as the as yet unenumerated count is not equal to what is needed to fill the list to the minimum required then randomly decide if the current item should be taken, otherwise take the item.Somethig like...
Source.Count() - Index = _minimum_required - _curr_count_of_items_taken _
OrElse GetRandomNumberBetween1And100() <= _probability_this_item_is_taken
' _minimum_required and _probability_this_item_is_taken are constants
The confounding part is that _curr_count_of_items_taken needs to be incremented each time the TakeWhile statement is satisfied. How would I go about doing that? I'm also open to a solution that uses any other LINQ methods (Aggregate, Where, etc.) instead of TakeWhile.If all else fails then I will go back to using a good old for-loop =)
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Mar 27, 2012
I have the following Data Transfer Objects defined:
Public Class MemberWithAddressesDTO
Public Property Member_PK As Integer
Public Property Firstname As String
Public Property DefaultAddress As AddressDTO
Public Property Addresses As IQueryable(Of AddressDTO)
End Class
[Code]...
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Jul 26, 2010
I currently have a View in MVC where I pass a single set of data to the view. However, I've come across a problem where I am having to use a LINQ query within a For Each loop in the View to pull out additional information from a SQL View of data from another DB.
The error I'm getting is Late binding operations cannot be converted to an expression tree.
The particular snippet I'm encountering the error on is:
[Code]...
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