When using VB.NET I can do the following:
Public Function GetUser(ByVal ID as Integer) As User
Dim dc As New YesEntities()
Return (From u in dc.Users Where u.ID = ID).Single()
End Function
And on my .aspx/.vbhtml page I can access the user's department name like this:
Dim DepartmentName as String = new User().GetUser(12).Department.Name
[Code]...
After I have programmed several projects in VB.Net I to my surprise discovered that there are some more than subtle differences between C# and VB.NET LINQ usage.For example, if we want to group elements by multiple properties (columns) we need to create a new anonymous type explicitly:
var procs = from c in Process.GetProcesses()
group c by new {c.BasePriority, c.Id} into d
select d;
whereas in VB.NET more straightforward syntax will already do:
Dim b = From c In Process.GetProcesses()
Group c By c.BasePriority, c.Id Into Group
Select Group
So, one does not need to create a type with "new" here. What are the other differences? good comparison between the LINQ syntax in C# and VB.NET?
I have a LINQ query to retrieve the maximum value of an integer column. The column is defined as NOT NULL in the database. However, when using the MAX aggregate function in SQL you will get a NULL result if no rows are returned by the query.Here is a sample LINQ query I am using against the Northwind database to demonstrate what I am doing.
var maxValue = (from p in nw.Products
where p.ProductID < 0
select p.ProductID as int?).Max();
C# correctly parses this query and maxValue has a type of int?. Furthermore, the SQL that is generated is perfect:
SELECT MAX([t0].[ProductID]) AS [value]
FROM [Products] AS [t0]
WHERE [t0].[ProductID] < @p0
The question is, how do I code this using VB.NET and get identical results? If I do a straight translation:
dim maxValue = (from p in Products
where p.ProductID < 0
select TryCast(p.ProductID, integer?)).Max()
I get a compile error. TryCast will only work with reference types, not value types. TryCast & "as" are slightly different in this respect. C# does a little extra work with boxing to handle value types. So, my next solution is to use CType instead of TryCast:
dim maxValue = (from p in Products
where p.ProductID > 0
select CType(p.ProductID, integer?)).Max()
This works, but it generates the following SQL:
SELECT MAX([t1].[value]) AS [value]
FROM (
SELECT [t0].[ProductID] AS [value], [t0].[ProductID]
[code]....
While this is correct, it is not very clean. Granted, in this particular case SQL Server would probably optimize the query it to be the same as the C# version, I can envisage situations where this might not be the case. Interestingly, in the C# version, if I use a normal cast (i.e. (int?)p.ProductID) instead of using the "as" operator I get the same SQL as the VB version. if there is a way to generate the optimal SQL in VB for this type of query?
I'm having trouble getting a Linq to Sql query to work. Basically, I want the sum of a column in a table for only rows matching a certain condition. A simplified version is this:
Orders = order that contains products
OrderProducts = relational table containing products that are in an order
Products = table containing information about products
I can get the total sum of the qty of products like this:
Dim totalQty = requests.Sum(Function(p) p.OrderProducts.Sum(Function(q) CType(q.ProductQty, Nullable(Of Integer))))
(Requests is a IQueryable of Orders)But I also need to get the sum of qty where the actual product meets a certain condition. Something like...
Dim totalQty = requests.Sum(Function(p) p.OrderProducts.Sum(Function(q) CType(q.ProductQty, Nullable(Of Integer))))... WHERE p.OrderProducts.Product.ProductAttribute = true
How would I go about getting that query with the additional where clause to only get the sum of the qtys where the productAttribute = true ?
I have the following query which groups some records and then filters where the count of the grouped records is 1.
I'd like to take the returned result and perform another query to retrieve the entire record from the JobcodesWorkingRollup table where the ParentNode column equals the result of this query:
Dim query = From r In context.GetTable(Of JobcodesWorkingRollup)() _
Group r By r.ParentNode Into g = Group _
Where g.Count = 1 _
Select New With {.cnt = g.Count, .nm = g.FirstOrDefault.ParentNode}
I'm experimenting with linq compount selects. I find the following query not to return any element:
Dim q = From s In d.GetChildRows("DossierSinistri") _
From i In s.GetChildRows("DossierIncarichi") _
Select s
[Code].....
Why can't I get any values back when I use Linq to Sql? BHS_TimeSheet is my database table in which have some records. Model.TimeSheet is a class I create in the model. Private db As DataFactoryDataContext
[Code]...
Today I ran into an issue with LINQ to objects (not SQL) that popped up due to a typo. I had a .Select one place and a .Where in another place. I was expecting same result but they are showing different numbers. Assume somelist has 10 elements with all elements having qty = 0
[Code]...
i try to select controls using LINQ but it show error
here is the code:
Dim testcontrol As VariantType
testcontrol = From cControl As Control In Me.Controls.OfType(PictureBox) Select cControl Order By Name Ascending
[Code].....
I have seen different examples in Linq and one used Select and another didnt but both return the same results. Is there a reason why we should use Select ?
[Code]...
I can't quite figure out why this Linq Statement isn't working as i would expect:
[Code]....
I would assume that this would create a new collection of anonymous types, that would be distinct. Instead it creates a collection the size of the "ThisParentCollection" with duplicate "MyAnonymousType" in it (duplicate id's).
So say I have a collection of Bloops
Class Bloop
Public FirstName
Public LastName
[Code]....
Is it possible using Linq to select the FirstName and LastName out of all the Bloops in the collection of Bloops and return a collection of Razzies? Or am i limited to a For-Loop to do my work?
To clear up any confusion, either VB or C# will do. Also this will probably lead to me asking the question of (What about using a "Where" clause).
I converted the following query from C#:
src.Select((c, i) => src.Substring(i)).Count(sub => sub.StartsWith(target))
To the VB.NET query:
src.[Select](Function(c, i) src.Substring(i)).Count(Function([sub]) [sub].StartsWith(target))
Using Developer Fusion. I was just wondering why the VB.NET version has [] throughout.
I have a single columned datatable inside a single tabled dataset.I just want to convert this dataset to distinct rows. Here is my code, it gives compile error '.' expected.
Dim query = _
From email In ds.Tables(0) _
Select email.Field<string>("Email").Distinct()
EDIT: I changed to (Of String) and it works... BUT NOW 'query' is an ienumerable collection of characters... not a datatable... so how do I convert back easily without manually doing a loop?
Linq to SQL query to Select the maximum "MeanWindSpeed" value? The database name is "WeatherArchives" The TableName is "TblValues" The Column is "MeanWindSpeed" And Also, I would like to have a query to get me the Max "MeanWindSpeed" in each year,
View 1 RepliesI've a collection with the data like this.[code]...
how can select the distinct data using linq?
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 need to have a query which list all the user according to the date value in the database. Problems is this, in the database the date format is 5/5/2009 4:30:12 but I want to compare with 5/5/2009. I think the value of the based date is 5/5/2009 12:00:00 and that's why I couldn't query it.
The query is something like
dim db = new databcontext
dim user = from u in db.datacontext where u.signUpTime = 5/5/2009 select u.
Dim orders = From tt In testTable _
Order By tt.Item("OrderNumber") _
Select tt.Item("OrderNumber"), tt.Item("OrderId")
This is breaking. Is there a way to do this? I would have thought it was easy enough. Obviously, I thought wrong....
I have this LINQ statement [code]...
Is there any way that I can use if/iif within select ?
I'm pretty new in Linq and the first problem I've is to select the Distinct values from a ObservableCollection( Of T)
I've tried with[code]...
My LINQ query:
Dim groupedData = (From p In pData _
Group By p.TruncParam Into Group) _
.SelectMany(Function(g) g.Group) _
.Select(Function(d, idx) New With { _
[Code]...
When the TruncParam changes, I would like the index (idx) in the Select clause to reset to 1. So, in the list above, the Index should be SOLUB0001, SOLUB0002, INSOL0001, INSOL0002...CLRES0001, SUMCA0001, SUME0001.
How should I alter the LINQ query?
[Code]...
I am trying to replace tasks.IndexOf(t) + 1 with something a little simpler. Is there any built in functionality for this? Hrmm xml literals do not seem to translate well on here....
I was wondering if there is a neat way do to this, that DOESN'T use any kind of while loop or similar, preferably that would run against Linq to Entities as a single SQL round-trip, and also against Linq To Objects. I have an entity - Forum - that has a parent-child relationship going on. That is, a Forum may (or in the case of the top level, may not) have a ParentForum, and may have many ChildForums. A Forum then contains many Posts.
What I'm after here is a way to get all the Posts from a tree of Forums - i.e. the Forum in question, and all it's children, grandchildren etc. I don't know in advance how many sub-levels the Forum in question may have. (Note - I know this example isn't necessarily a valuble use case, but the Forum object model one is one that is familar to most people, and so serves as a generic and accessible premise rather than my actual domain model.)
I have a listbox that is dynamically filled by certain values depending on what table has been selected from another list box. Once a value is selected, it is being graphed vs a date & time range. With my ignorance of linq: depending on what value is selected, the linq to sql statement I need to create to grab data from my database is different as I can't use an index on an anonymous type.
result = From t In db.APS _
Where t.DateTime >= startDate And _
t.DateTime <= finishDate And t.Weight = weight _
Select t.DateTime, t.TotalConcentration
t.TotalConcentration should be selected if my listbox value is "Total Concentration", but if it's something else, like "Temperature" or "Flow Rate" (connected to appropreate database columns) - this method obviously isn't going to work. I need to be able to dynamically select a specific column from the anonymous type list, or use some other method I'm unaware of to do this.
Can I use LINQ to return an item in a collection that is the same TYPE as the items in the collection? I am a LINQ Noob trying to avoid looping.
Dim mostRecentlyCreatedQuestionnaire As ParentQuestionnaireItem =
CType((From P In questionnaireCollection Order By P.Metadata.CreateDate Descending).Take(1), ParentQuestionnaireItem)
I get an "unable to CAST" error when I include the CTYPE function. I kind of expected that error, but I imagine that if I coul dnot do this, LINQ's usefulness would be diminished and therefore assume that there must be a way..
For I've tried this:Dim exampleItems As Dictionary(Of String, String) = New Dictionary(Of String, String)
Dim blah = exampleItems.Select (Function(x) New (x.Key, x.Value)).ToList 'error here
But I'm getting a syntax error and all the examples that I've seen are in C#.
I'm using LINQ to SQL to select some columns from one table. I want to get rid of the duplicate result also.
Dim customer = (From cus In db.Customers Select cus.CustomerId, cus.CustomerName).Distinct
Result:
1 David
2 James
1 David
3 Smith
2 James
5 Joe
Wanted result:
1 David
2 James
3 Smith
5 Joe
Can anyone show me how to get the wanted result?
I'm developing a piece of a system that basically migrates data from one set of tables to another set. Everything works fine, but I've decided to employ transactions instead of just failing on things that are partially completed. (That is, if some exception occurs, I want to rollback instead of having partial data migrated.)
I have a service (in the 3-tier architecture way, not web) which begins a transaction on the data access layer. The data context is shared in the data access class which contains many methods. Those methods use various LINQ-to-SQL techniques to update/insert/delete. All the LINQ-to-SQL "selects" are within CompiledQueries. [code]...
I have done a lot of searching to what appears to be a simple LINQ problem but I can't figure out how to do grab an object out of a collection that has a specified minimum (or max value) without resorting to a sort like this[code]...
View 3 Replies