Linq query to list VB.NET

Question

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)'.

Make sure you have Option Strict On. If you have Option Strict Off, your Query may be infering the result as IEnumerable(Of Object) rather than string and ToList isn't casting it properly. Otherwise, remove the As List(Of String) and see what type inferencing returns. I suspect you have an implicit cast happening somewhere that the compiler is hiding. — Jim Wooley
– Jim Wooley, Commented Sep 2, 2011 at 17:36

Reed Copsey · Accepted Answer · 2011-09-02 16:43:39Z

13

Your error message suggests the query is actually a List(Of T) containing a collection internally.

If this is the case, you can use SelectMany to flatten the collection:

Dim values As List(Of String) = query.SelectMany(Function(m) m).ToList()

Edit: Given your edit, as well as the comment, the following should work fine:

Dim values As List(Of String) = query.ToList()

edited Sep 2, 2011 at 16:43

answered Sep 2, 2011 at 16:05

Reed Copsey

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8 Comments

serhio Over a year ago

not seems to work: Value of type 'System.Collections.Generic.List(Of System.Collections.Generic.IEnumerable(Of Char))' cannot be converted to 'System.Collections.Generic.List(Of String)'.

Reed Copsey Over a year ago

@serhio: mmm - if that's the case, then .ToList() should work fine.

Reed Copsey Over a year ago

Edited my answer - that's effectively the same as what you're doing in the "good old method"...

serhio Over a year ago

As I indicatd in the post, such a method does not exist. ToList, because "query" is IEnumerable(Of String)

Sven Over a year ago

@serhio: The LINQ extension method Enumerable.ToList works just fine on an IEnumerable(Of String). Your first version should work.

|

avanek · Accepted Answer · 2011-09-02 17:29:33Z

1

Perhaps you should try to specify the type on the query variable?

Dim query = From o In myContainer.MyObjects Select o.MyStringProperty Distinct

Should become

Dim query As IEnumerable(Of String) = From o In myContainer.MyObjects Select o.MyStringProperty Distinct

If the type of IEnumerable(Of String) can't be used on query, then you need to flatten the list as Reed Copsey said.

answered Sep 2, 2011 at 17:29

avanek

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Comments

GrahamJ · Accepted Answer · 2022-04-05 09:12:01Z

0

This works for me:

Dim drs As List(Of ProjectTask) = (From pt In projectTasks Where pt.TaskEngineerId <> 1).ToList()

Putting brackets around the query did the trick.

answered Apr 5, 2022 at 9:12

GrahamJ

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Comments

serhio · Accepted Answer · 2011-09-02 16:48:38Z

-1

Finally, solved with good old method : )

  Dim values As New List(Of String)

  For Each item In query
    values.Add(item)
  Next item

answered Sep 2, 2011 at 16:48

serhio

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4 Comments

Yatrix Over a year ago

Your question was how to do something with Linq. You shouldn't incorrectly answer your own question and then accept it.

Faizan Mubasher Over a year ago

@Yatrix Don't worry! Up votes will reveal the result :-)

Yatrix Over a year ago

@FaizanMubasher Sure, but the fact still remains this is the wrong answer.

Faizan Mubasher Over a year ago

This is what I am saying. Up votes are revealing what is right answer :-)

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