LINQ Cookbook, Recipe 10: Pre-compiling Queries for Performance (Doug Rothaus)

re: LINQ Cookbook, Recipe 10: Pre-compiling Queries for Performance (Doug Rothaus)

lewcifer — Fri, 08 Oct 2010 11:22:55 GMT

Okay I have got this working by making the following changes:

Return orderQuery(db, pCity)

End Function

Call to populate grid is:

If lbCity.SelectedValue IsNot Nothing Then

DataGridView1.DataSource = GetData(lbCity.SelectedValue).ToList()

End If

re: LINQ Cookbook, Recipe 10: Pre-compiling Queries for Performance (Doug Rothaus)

lewcifer — Fri, 08 Oct 2010 07:11:59 GMT

Hello

I am trying to do something similar in order to create a compiled query for reuse and using your code have created the same GetData function and variable using my own data context tables

Private orderQuery As Func(Of HCADataContext, String, IQueryable(Of T_HCA_Suministro))

Private Function GetData(ByVal pCity As String) As IQueryable(Of T_HCA_Suministro)

' If the query for orders has not been compiled yet, compile it. Otherwise,

' use the compiled query.

If orderQuery Is Nothing Then

orderQuery = CompiledQuery.Compile( _

Function(database As HCADataContext, pLocal As String) _

From data In db.T_HCA_Suministro

Where data.HCAPS_Localidad = pLocal

Select data)

'From data In db.T_HCA_Suministro

' Where data.HCAPS_Localidad Is pLocal

' Select CUPS = data.HCAPS_CUPS, Localidad = data.HCAPS_Localidad, Provincia = data.T_Tipo_Provincias.Pr_Nombre)

End If

' Execute the compiled query by calling the ToList method and

' return the results.

Return orderQuery(db, pCity).ToList()

End Function

Call to populate grid is:

If lbCity.SelectedValue IsNot Nothing Then

DataGridView1.DataSource = GetData(lbCity.SelectedValue)

End If

With the ToList method I am receiving the error:

No se puede convertir un objeto de tipo 'System.Collections.Generic.List`1[LINQ_Test_2.T_HCA_Suministro]' al tipo 'System.Linq.IQueryable`1[LINQ_Test_2.T_HCA_Suministro]'.

If I remove the toList method I receive no error but the data is not displayed in the datagridview even though I can see that the datagridviews datasource contains the correct data.

Any ideas where I might be going wrong?

Content Rollup for November and December

Noticias externas — Fri, 04 Jan 2008 19:04:56 GMT

Here's a summary of all the content the VB team members, including myself, have created for you on

re: LINQ Cookbook, Recipe 10: Pre-compiling Queries for Performance (Doug Rothaus)

DougR — Tue, 13 Nov 2007 04:04:46 GMT

It's not a type-safety issue. It's just syntax. VB doesn't support the second syntax example for jagged arrays.

re: LINQ Cookbook, Recipe 10: Pre-compiling Queries for Performance (Doug Rothaus)

Fduch — Sun, 11 Nov 2007 02:53:39 GMT

Sorry for offtopic, but... Why are we forced to write

Dim data As Integer()()() = {New Integer()() {New Integer() {1, 2}, New Integer() {2, 3}}}

instead of

Dim data As Integer()()() = {{{1, 2},{2, 3}}}

Isn't it typesafe?