Why my LINQ query doesn't work was expected?[Answered] RSS

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Last post Mar 08, 2016 08:34 PM by jacobpressures

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JacobPressur...

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Why my LINQ query doesn't work was expected?

Mar 07, 2016 11:14 PM|JacobPressures|LINK

My linq query works pretty good until i get to group by. I took a PluralSight class and it said that Linq can end in a Group By clause or a Select clause. However, in my VB.NET project, if i put Group By, it tells me "into is expected." These are very simple queries. I'm able to get it to work, but... I have to use syntax that I don't understand. The PluralSight course was on C# but I've seen queries online that uses the same query syntax that I'm using.

Here is the object I created to test linq out.

Public Class Author
        Private m_name As String
        Private m_age As Short
        Private title As String
        Private mvp As Boolean
        Private pubdate As DateTime
        Private m_city As String
        Public Sub New(name As String, age As Short, title As String, mvp As Boolean, pubdate As DateTime, city As String)
            Me.m_name = name
            Me.m_age = age
            Me.title = title
            Me.mvp = mvp
            Me.pubdate = pubdate
            Me.m_city = city
        End Sub
        Public Property Name() As String
            Get
                Return m_name
            End Get
            Set(value As String)
                m_name = value
            End Set
        End Property
        Public Property Age() As Short
            Get
                Return m_age
            End Get
            Set(value As Short)
                m_age = value
            End Set
        End Property
        Public Property BookTitle() As String
            Get
                Return title
            End Get
            Set(value As String)
                title = value
            End Set
        End Property
        Public Property IsMVP() As Boolean
            Get
                Return mvp
            End Get
            Set(value As Boolean)
                mvp = value
            End Set
        End Property
        Public Property PublishedDate() As DateTime
            Get
                Return pubdate
            End Get
            Set(value As DateTime)
                pubdate = value
            End Set
        End Property
        Public Property City() As String
            Get
                Return m_city
            End Get
            Set(value As String)
                m_city = value
            End Set
        End Property
    End Class

Afterwards I instantiate several objects and then try to create a Linq query.

Dim AuthorList As New List(Of Author)()
        AuthorList.Add(New Author("Mahesh Chand", 35, "A Prorammer's Guide to ADO.NET", True, New DateTime(2003, 7, 10), "Mobile"))
        AuthorList.Add(New Author("Neel Beniwal", 18, "Graphics Development with C#", False, New DateTime(2010, 2, 22), "Mobile"))
        AuthorList.Add(New Author("Praveen Kumar", 28, "Mastering WCF", True, New DateTime(2012, 1, 1), "Mobile"))
        AuthorList.Add(New Author("Mahesh Chand", 35, "Graphics Programming with GDI+", True, New DateTime(2008, 1, 20), "Mobile"))
        AuthorList.Add(New Author("Raj Kumar", 30, "Building Creative Systems", False, New DateTime(2011, 6, 3), "Mobile"))
        AuthorList.Add(New Author("Mahesh Patel", 35, "A Prorammer's Guide to ADO.NET", True, New DateTime(2003, 7, 10), "Atlanta"))
        AuthorList.Add(New Author("Neel Patel", 18, "Graphics Development with C#", False, New DateTime(2010, 2, 22), "Atlanta"))
        AuthorList.Add(New Author("Praveen Patel", 28, "Mastering WCF", True, New DateTime(2012, 1, 1), "Atlanta"))
        AuthorList.Add(New Author("Mahesh Patel", 35, "Graphics Programming with GDI+", True, New DateTime(2008, 1, 20), "Pensacola"))
        AuthorList.Add(New Author("Raj Patel", 30, "Building Creative Systems", False, New DateTime(2011, 6, 3), "Pensacola"))


'These two queries work with no problems:

Dim PeopleOfAtlanta = (From author In AuthorList
                      Where author.City = "Atlanta"
                      Select author).ToList
 
Dim PeopleNames = (From author In AuthorList
                     Where author.City = "Atlanta"
                     Select author.Name).ToList

'These two queries do not work:

Dim People = (From author In AuthorList
             Group By author.City).ToList

Dim People2 = (From author In AuthorList
             Group author By author.City).ToList

'This gives me the error: "into is expected."

'If I add into and put a group name afterward, it will add parenthesis to the end. For example:

Dim People = (From author In AuthorList
                     Group By author.City Into authorGroups()).ToList

'If i add a select statement was I was told during the PluralSight course (basically PluralSight said that if i add an INTO clause, 
'i will need a select
'VS still adds parenthesis at the end of the into clause.

Dim People = (From author In AuthorList
                     Group By author.City Into authorGroups()
                     Select authorGroups).ToList

'In addition to this, Visual Studio gives me red squeakly lines in Solution Explore. The error message I'm getting is "Definition of method 
'authorGroups is not accessible in this context."

' The only thing I can get to work are the following:

Dim People = (From author In AuthorList
                     Group By author.City).ToList
                     Into AuthorsByCity = Group).ToList

' I don't understand why I need the into statement or set it equal to Group. I don't understand this syntax it seems counter-intuitive. 

'Thanks very much!

- Reply
Candice Zhou
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2021 Posts
Re: Why my LINQ query doesn't work was expected?

Mar 08, 2016 03:07 AM|Candice Zhou|LINK
Hi jacobpressures,

Group By Clause in VB is different from C#. Groups the elements of a query result. Can also be used to apply aggregate functions to each group. The grouping operation is based on one or more keys.

Syntax:
```
Group [ listField1 [, listField2 [...] ] By keyExp1 [, keyExp2 [...] ]
  Into aggregateList
```
Please see: https://msdn.microsoft.com/en-us/library/bb531412.aspx

Best Regards,

Candice Zhou
- Reply
JacobPressur...
Member

23 Points

65 Posts

Re: Why my LINQ query doesn't work was expected?

Mar 08, 2016 08:34 PM|JacobPressures|LINK

Thanks! I got a book to try to help me understand the logic of this query. It seems unnecessarily verbose and confusing.