I have a listbox which users can select from a list if Towns, I want to be able to build a LINQ query based on the selected items in the list e.g.
Dim ddlTowns As ListBox = CType(Filter_Accommodation1.FindControl("ddlTowns"), ListBox)
If Not ddlTowns Is Nothing Then
For Each Item In ddlTowns.Items
If Item.Selected Then
'// Build query
End If
Next
End If
I have researched LinqKit as it appears to be able to do what I need but I cannot after hours of trying make any headway. I cannot find anything in VB which translates in anything meaningful or usable.
Just had a Eureka moment and rather than using predicate I came up with this...
Private Function Filter_Accommomdation_QueryBuilder() As IEnumerable
Dim ddlTowns As ListBox = CType(Filter_Accommodation1.FindControl("ddlTowns"), ListBox)
Dim myList As New List(Of String)
If Not ddlTowns Is Nothing Then
For Each Item In ddlTowns.Items
If Item.Selected Then
myList.Add(Item.value)
End If
Next
End If
Dim Filter_Query = _
From c In InitialQuery _
Where myList.ToArray.Contains(c.MyData.element("townvillage").value) _
Select c
Return Filter_Query
End Function
As a note I'm using c.MyData as the nature of InitialQuery demands a number of structured fields (the query is reused from various tables which by poor design aren't very consistant).
Check out this question - contains some useful VB examples for you: Using PredicateBuilder with VB.NET
Related
I'm not a experience vb.net programmer so I'm struggling with some code related to treeview node implementation:
My goal is to implement a hierarchical and editable structure related to a "Bill of Materials" (e.g. a house has a foundation, walls, roof,.. and walls has stones, plaster,....)
The number of levels of this hierarchical structure is (per definition) unknown.
I'm able to populate a treeview(1) with SQL data to multiple but a fixed number of levels.
The code I've implemented:
TreeView1.Nodes.Add(var01, var01).Nodes.Add(var02, var02) (example 2 levels)
where var01 and var02 the names within the structure are (e.g. House-Wall). The Node structure is build using a "for - next loop"
Officious by adding ".Nodes.Add(varXX, varXX)" I'm able to extend the level of the structure.
My goal however is to implement "the adding of .Nodes.Add(varXX, varXX)" through a loop make the number of hierarchical levels flexible.
I tried to convert Treeview1.Nodes... to a string and build a (overall) string through a loop. Then I tried to convert this string to the treeview control. This principle doesn't unfortunately work.
Any advice would be appreciated.
Try something like this:
Public Function GetBOMTree() As TreeNode
Dim BOMTable As DataTable
' Assuming your hierarchy is small enough to do a full table load into BOMTable, put your SQL statements here
Dim BOMDictionary = BOMTable.Rows.Cast(Of DataRow) _ ' Assumed to be a data table
.Where(Function(F) F.Item("ParentKey").GetType IsNot GetType(DBNull)) _
.GroupBy(Function(F) CInt(F.Item("ParentKey"))) _ ' Assuming integer keys
.ToDictionary(Function(F) F.Key)
Dim Root = BOMTable.Rows.Cast(Of DataRow) _
.Where(Function(F) F.Item("ParentKey").GetType Is GetType(DBNull)) _
.FirstOrDefault
If Root IsNot Nothing Then
Dim GetTree As Func(Of DataRow, TreeNode) = ' The "as Func" is necessary to allow recursion
Function(D As DataRow) As TreeNode
Dim Result As New TreeNode
Dim Key = CInt(D.Item("PrimaryKey"))
Result.Tag = Key
Result.Text = CStr(D.Item("Description"))
If BOMDictionary.ContainsKey(Key) Then
Dim Children = BOMDictionary.Item(Key)
For Each Child In Children.OrderBy(function(F) cstr(f.item("Description")))
Result.Nodes.Add(GetTree(Child))
Next
End If
Return Result
End Function
Return GetTree(Root)
Else
Return Nothing
End If
End Function
The way this works is using a little recursion, and some LINQ to objects to get an initial dictionary. I've made the assumption that your hierarchy is in you table and not an external table, but if it's external, you can modify what you see here to make it work. I've assumed integer keys. Code is trivial to modify if you are using GUID's, just cast appropriately.
I would like to convert ForEach to LINQ. Currently I'm using these two parts
If TypeOf e.FilterPopup Is RadListFilterPopup Then
Dim ePopup As RadListFilterPopup = DirectCast(e.FilterPopup, RadListFilterPopup)
Dim childList As New List(Of Object)()
For Each row As GridViewRowInfo In Me.grdCNCFilesRad.ChildRows
Dim value = row.Cells(e.Column.Index).Value
If Not childList.Contains(value) Then
childList.Add(value)
End If
Next
Dim newPopup As New RadListFilterPopup(e.Column)
For Each item As System.Collections.ArrayList In ePopup.MenuTreeElement.DistinctListValues.Values
If Not childList.Contains(item(0)) Then
newPopup.MenuTreeElement.DistinctListValues.Remove(item(0).ToString())
End If
Next
e.FilterPopup = newPopup
End If
How can I do the same with a LINQ query?
I don't know what your variable grdCNCFilesRad is type of, but I assume it is no .NET type. But when I read ChildRows then I can be sure that this is some sort of enumeration (somewhere in it's inheritance tree must be the interface IEnumerable).
So you can include System.Linq and apply a AsQueryable() at your ChildRows.
The rest is just a little bit of Linq (Select, Where, ToList()). That's it!
Edit:
The first part should be solved by this:
Dim childList =
Me.grdCNCFilesRad.ChildRows
.AsQueryble()
.Select(Function(row) row.Cells(e.Column.Index).Value)
.Distinct()
There is no need of converting ForEach with Linq if you go for performance issues.
Your existing foreach code looks good.
Note: Don't think Linq is better compared to for-each in performance.
I'm developing an application to allow engineers to conduct simple single table/view queries against our databases by selecting Database, Table, Fields.
I get how to use the Dynamic LINQ Library Sample to provide for dynamically selecting the Select, Where and Order by Clauses at runtime but I'm at an impass on how to allot for table choice.
Is there a way to provide for dynamically selecting the "from" table at run time, and if how could you provide some concrete example or point me in the direction of someone who has?
Thank You ever so much.
EDIT
So Both of the answers seem to be saying the same general Idea. I'm going to try to convert the C# into VB and get it to work.
The first answer converts to
NotInheritable Class DataContextExtensions
Private Sub New()
End Sub
<System.Runtime.CompilerServices.Extension> _
Public Shared Function GetTableByName(context As DataContext, tableName As String) As ITable
If context Is Nothing Then
Throw New ArgumentNullException("context")
End If
If tableName Is Nothing Then
Throw New ArgumentNullException("tableName")
End If
Return DirectCast(context.[GetType]().GetProperty(tableName).GetValue(context, Nothing), ITable)
End Function
End Class
but it's tossing me an Error stating that Extension methods can be defined only in modules.
But when I wrap it in module tags it still gives the same error.
So I got it to compile by wrapping it in Module Tags and stripping the class tags. Also I can pull the last line out of it and shove that directly into my base method which allows my to execute it but, it seems to be coming back empty. When I try to enumerate the results there are none. Not sure if this is my codes problem or the new codes issue, I'll test more.
Here's my conversion of the second Example, Now I'm off to try to see if I can get them to work. I'll be back with questions or results after some testing.
'get the table from a type (which corresponds to a table in your context)
Dim dataContextNamespace = "My.DataContext.Namespace"
Dim type = Type.[GetType](dataContextNamespace + tableName)
Dim table = dc.GetTable(type
'add where clauses from a list of them
For Each whereClause As String In whereClauses
table = table.Where(whereClause)
Next
'generate the select clause from a list of columns
Dim query = table.[Select]([String].Format("new({0})"), [String].Join(",", selectColumns))
Thanks for the help. BBL
See Get table-data from table-name in LINQ DataContext.
This is probably actually better done by using direct SQL statements. LINQ will just get in your way.
VB Conversion:
NotInheritable Class DataContextExtensions
Private Sub New()
End Sub
<System.Runtime.CompilerServices.Extension> _
Public Shared Function GetTableByName(context As DataContext, tableName As String) As ITable
If context Is Nothing Then
Throw New ArgumentNullException("context")
End If
If tableName Is Nothing Then
Throw New ArgumentNullException("tableName")
End If
Return DirectCast(context.[GetType]().GetProperty(tableName).GetValue(context, Nothing), ITable)
End Function
End Class
Usage:
Dim myDataContext as New MyCustomDataContext
myDataContext.GetTableByName("ORDERS").Where("...")
You can use GetTable() to get the corresponding ITable of your data. Then coupled with using DLINQ, making it relatively easy.
This example uses the AdventureWorks database. My project has the context defined in the DatabaseTest assembly in the DatabaseTest.AdventureWorks namespace.
'' need my database and DLINQ extensions up top
Imports DatabaseTest.AdventureWorks
Imports System.Linq.Dynamic
'' sample inputs
Dim dc = New AdventureWorksDataContext()
Dim tableName = "Contact"
Dim whereClauses() = {"FirstName = ""John"" OR LastName = ""Smith"""}
Dim selectColumns() = {"FirstName", "LastName"}
'' get the table from a type (which corresponds to a table in your database)
Dim typeName = "DatabaseTest.AdventureWorks." & tableName & ", DatabaseTest"
Dim entityType = Type.GetType(typeName)
Dim table = dc.GetTable(entityType)
Dim query As IQueryable = table
'' add where clauses from a list of them
For Each whereClause As String In whereClauses
query = query.Where(whereClause)
Next
'' generate the select clause from a list of columns
query = query.Select(String.Format("new({0})", String.Join(",", selectColumns)))
In retrospect, using reflection might have been the easier way to get the table since you have the name already. But then the names might not have a 1-to-1 correspondence so you'll have to compensate for it.
Dim table As ITable = dc.GetType().GetProperty(tableName & "s").GetValue(dc, Nothing)
Currently we have a large DataTable (~152k rows) and are doing a for each over this to find a sub set of distinct entries (~124K rows). This is currently taking about 14 minutes to run which is just far too long.
As we are stuck in .NET 2.0 as our reporting won't work with VS 2008+ I can't use linq, though I don't know if this will be any faster in fairness.
Is there a better way to find the distinct lines (invoice numbers in this case) other than this for each loop?
This is the code:
Public Shared Function SelectDistinctList(ByVal SourceTable As DataTable, _
ByVal FieldName As String) As List(Of String)
Dim list As New List(Of String)
For Each row As DataRow In SourceTable.Rows
Dim value As String = CStr(row(FieldName))
If Not list.Contains(value) Then
list.Add(value)
End If
Next
Return list
End Function
Using a Dictionary rather than a List will be quicker:
Dim seen As New Dictionary(Of String, String)
...
If Not seen.ContainsKey(value) Then
seen.Add(value, "")
End If
When you search a List, you're comparing each entry with value, so by the end of the process you're doing ~124K comparisons for each record. A Dictionary, on the other hand, uses hashing to make the lookups much quicker.
When you want to return the list of unique values, use seen.Keys.
(Note that you'd ideally use a Set type for this, but .NET 2.0 doesn't have one.)
ok this is the thing I have right now which is working quite well except its a bit slow:
Public Function GetList() As List(Of SalesOrder)
Try
Dim list As New List(Of SalesOrder)
Dim ds As DataSet
ds = cls.GetSalesOrderList 'CLS is the data access class
For i = 0 To ds.Tables(0).Rows.Count - 1
Dim row As DataRow = ds.Tables(0).Rows(i)
Dim kk As SalesOrder = New SalesOrder()
kk.ID = Val(row.Item("id") & "")
kk.SalesOrderNo = row.Item("salesorderid") & ""
kk.SalesOrderDate = row.Item("OrderDate") & ""
kk.CustomerId = Val(row.Item("customerid") & "")
list.Add(kk)
Next
Return list
Catch ex As Exception
Throw ex
End Try
End Function
Now once I start retrieving more than 10000 records from the table, the loop takes long time to load values into generic class. Is there any way that I can get rid of loop? Can I do something like the following with the generic class?
txtSearch.AutoCompleteCustomSource.AddRange(Array. ConvertAll(Of DataRow, String)(BusinessLogic.ToDataTable.ConvertTo(WorkOr derList).Select(), Function(row As DataRow) row("TradeContactName")))
I would have thought the problem isn't with doing a loop but with volumes of data. Your loop method seems to process each bit of data only once so there isn't any massive efficiency crash (such as looping over the dataset once and then again for each row or that kind of thing). Any method you choose is at the end of the day going to have to loop through all your data.
Their methods might be slightly more efficient than yours but they aren't going to be that much more so I'd think. I'd look at whether you can do some refactoring to reduce your data set (eg limit it to a certain period or similar) or whether you can do whatever searching or aggregating of that list you intend in the database instead of in code. eg if you're just going to sum the values of that list then you can almost certainly do it better by having a stored procedure that will do the summing on the database rather than in the code.
I know this hasn't directly answered your question but this is mainly because I don't know of a more efficient method. I took the question as asking for optimisation in general though rather than how to do this specific one. :)
Converting the loop into some kind of LINQ construct isn't necessarily going to improve performance if you're still enumerating over every row at once. You could return IEnumerable(Of SalesOrder) if you don't need to give the consumer the ability to add/remove from the list (which it looks like might be the case), and then in that case you could create an enumerator to handle this. That way, the dataset is loaded all at once, but the items are only converted into objects when they're being enumerated over, which may be part of your performance hit.
Something like this:
Return ds.Tables(0).Rows.Select(Function(dr As DataRow) Return New SalesOrder ... );
My VB with LINQ is a little rusty, but something to that effect, where the ... is the code to instantiate a new SalesOrder. That will only create a new SalesOrder object as the IEnumerable(Of SalesOrder) is being enumerated over (lazy, if you will).
Hey Paul, You mean something like below code
Dim list As New List(Of SalesOrder)
Dim kk As SalesOrder = New SalesOrder()
Function DrToOrder(dr as datareader)
kk.ID = Val(dr.Item("id") & "")
kk.SalesOrderNo = dr.Item("salesorderid") & ""
list.Add(kk)
End function
Function LoadData()
datareader.Rows.Select(DrToOrder)
End function
Are you talking about something like above code?