I try to buid a method to add a where clause to a Linq-to-SQL request (return an IQueryable). I try several methods but always use ToString, Indexof... but this result is a sql request take all element and the filter made in linq. I see request in SQL Server profiler.
I want a method to do it with result is a sql request with where include inside
I work in Visual Studio 2017 with SQL Server 2016. I code in vb.net
I see an interesting thing in linq dynamic library. But I can't to adapt to my situation
<Extension()> _
Public Function Where(ByVal source As IQueryable, ByVal predicate As String, ByVal ParamArray values() As Object) As IQueryable
If source Is Nothing Then Throw New ArgumentNullException("source")
If predicate Is Nothing Then Throw New ArgumentNullException("predicate")
Dim lambda As LambdaExpression = DynamicExpression.ParseLambda(source.ElementType, GetType(Boolean), predicate, values)
Return source.Provider.CreateQuery( _
Expression.Call( _
GetType(Queryable), "Where", _
New Type() {source.ElementType}, _
source.Expression, Expression.Quote(lambda)))
End Function
But I don't need all this complex strucutre. It's some years I buid my utilities. But Need to upgrade it. Here my code of my utilities
<Extension()>
Public Function Where(ByVal source As IQueryable, ByVal predicate As String) As IQueryable
Dim param = Expression.Parameter(GetType(String), "x")
Return source.Provider.CreateQuery(
Expression.Call(
GetType(Queryable), "Where",
New Type() {source.ElementType},
source.Expression, Expression.Quote(Expression.Lambda(Expression.Constant(predicate), param))))
End Function
Public Function TFOAppliqueFiltreTri(Of T, MaClassDatas As Class)(Origins As IQueryable(Of T), ByVal MesDonnees As TableFullOption.PagerTabEnCours(Of MaClassDatas)) As IQueryable(of T)
Dim retour As New TableFullOption.LstRetour
'Colonne de filtre
Dim strWh As String = ""
Dim Filtredrecords As IQueryable(Of T)
For Each Sort In MesDonnees.MesOptions
Dim colName = Sort.ColName
If strWh.Length > 0 Then strWh = strWh & " AND "
strWh = strWh & String.Format(colName & " like '%{0}%'", Sort.Search)
Next
If strWh.Length > 0 Then
Filtredrecords = Origins.Where(strWh) '<- Here call Where
Else
Filtredrecords = Origins
End If
Return Filtredrecords
End Function
I get this error:
Aucune méthode générique 'Where' sur le type 'System.Linq.Queryable' n'est compatible avec les arguments de type et les arguments fournis..
Then my problem is to write correctly lambda expression. My predicate argument is : Column1 like '%aaa%'. I want rewrite where method of dynamicLinq to accept string argument :Column1 like '%aaa%' directly
Thanks for your help
Finally after lot of reading in google and few feelings and certainly lot of chance.
Public Function Where(Of TEntity)(source As IQueryable(Of TEntity), searchColumn As List(Of String), searchValue As String) As IQueryable(Of TEntity)
Dim cond As Expression = Nothing
Dim ParamExpr = Expression.Parameter(GetType(TEntity), "x")
Dim conCat2 = GetType(String).GetMethod("Concat", New Type() {GetType(String), GetType(String)})
Dim conCat4 = GetType(String).GetMethod("Concat", New Type() {GetType(String), GetType(String), GetType(String), GetType(String)})
Dim Delim = Expression.Constant("/")
Dim DateName = GetType(SqlFunctions).GetMethod("DateName", New Type() {GetType(String), GetType(Nullable(Of DateTime))})
Dim DatePart = GetType(SqlFunctions).GetMethod("DatePart", New Type() {GetType(String), GetType(Nullable(Of DateTime))})
Dim DblToString = GetType(SqlFunctions).GetMethod("StringConvert", New Type() {GetType(Nullable(Of Double))})
For Each cn In searchColumn
For Each colName In cn.Split("|")
If Not colName.estVide Then
Dim body As Expression = ParamExpr
For Each member In colName.Split(".")
body = Expression.PropertyOrField(body, member)
Next
Dim Tostr As Expression
If body.Type.FullName.Contains("String") Then
Tostr = body
ElseIf body.Type.FullName.Contains("DateTime") Then
Dim day = Expression.Call(Expression.Call(conCat2, Expression.Constant("0"), Expression.Call(DateName, Expression.Constant("day"), body)), "Substring", Nothing, Expression.Constant(0), Expression.Constant(2))
Dim Month = Expression.Call(DatePart, Expression.Constant("MM"), body)
Dim toDouble = Expression.Convert(Month, GetType(Nullable(Of Double)))
Dim mois = Expression.Call(conCat2, Expression.Constant("0"), Expression.Call(Expression.Call(DblToString, toDouble), "Trim", Nothing))
Dim an = Expression.Call(DateName, Expression.Constant("year"), body)
Tostr = Expression.Call(conCat2, Expression.Call(conCat4, day, Delim, mois, Delim), an)
Else
Tostr = Expression.Call(body, "Convert.ToString", Nothing)
'Tostr = Expression.Convert(body, GetType(String))
End If
Dim condPart = Expression.Call(Expression.Call(Tostr, "ToLower", Nothing), "Contains", Nothing, Expression.Call(Expression.Constant(searchValue), "ToLower", Nothing))
If cond Is Nothing Then
cond = condPart
Else
cond = Expression.OrElse(cond, condPart)
End If
End If
Next
Next
Return source.Provider.CreateQuery(Of TEntity)(Expression.Call(GetType(Queryable), "Where", New Type() {GetType(TEntity)}, source.Expression, Expression.Lambda(cond, ParamExpr)))
End Function
Now I've dynamic filter which generated a SQL request with complete clause where
I am trying to add a value from DataTable dtUsers into a list UserLocations however I am getting the title error.
My code is:
Public UserLocations As New List(Of String())
For Each NewRow As DataRow In dtUsers.Rows
Dim seq As String = NewRow("SEQUENCE").Value.ToString
If CandRow("SQ") = NewRow("SQ") Then
UserLocations.Add(seq)
End If
Next
I don not understand why I cannot add a string to a list of strings.
How should I go about this?
Public UserLocations As New List(Of String)
For Each NewRow As DataRow In dtUsers.Rows
Dim seq As String = NewRow("SEQUENCE").Value.ToString()
If CandRow("SQ") = NewRow("SQ") Then
UserLocations.Add(seq)
End If
Next
I'm trying to populate a List using a DataTable, I have a for each loop that checks every row and adds the item to the list. But the code isn't working, I keep getting the error..
System.NullReferenceException: {"Object reference not set to an
instance of an object."}
-Data: {System.Collections.ListDictionaryInternal}
-HelpLink: Nothing -Inner Exception: Nothing
-TargetSite: {System.Collections.Generic.List`1[System.String] getListOfUsers()}
This is my code...
Function getListOfUsers() As List(Of String)
'Dim i As Integer = 0
Dim lUserNames As List(Of String) = Nothing
Dim dt As DataTable = getDataTable(db_Config, "SELECT * FROM tblUsers")
If dt.Rows.Count > 0 Then
Try
For Each dRowItem As DataRow In dt.Rows
'i = i + 1
'If IsDBNull(dt.Rows(0)("fldUserName").ToString) = False Then
' lUserNames.Add(dt.Rows(0)("fldUserName").ToString)
'End If
If dRowItem.Item("fldUserName").ToString <> "" Then
lUserNames.Add(dRowItem.Item("fldUserName").ToString)
End If
Next dRowItem
Catch ex As Exception
MsgBox(ex.ToString)
End Try
End If
Return lUserNames
End Function
Currently lUserNames has not been initialized. You need to do this:
Dim lUserNames As New List(Of String)
You have declared the List, but you haven't initialized it.
So change
Dim lUserNames As List(Of String) = Nothing
to
Dim lUserNames As List(Of String) = New List(Of String)
Of course you would also get a NullReferenceException if getDataTable returns Nothing instead of an empty DataTable if tblUsers would be empty at If dt.Rows.Count > 0.
You're not initializing your List on line 4. It should be:
Dim lUserNames As List(Of String) = New List(Of String)()
Edit: apparently this is a bit of a CSharp'ism :) This also works:
Dim lUserNames As New List(Of String)
I'm trying to get the results from a Dynamic LINQ query into a DataTable. Trying to get the query directly into a DataTable gives me this error:
Unable to cast object of type 'System.Linq.EnumerableQuery`1[DynamicClass1]' to type 'System.Data.DataTable'.
My code is:
Dim query = tbl.AsEnumerable.AsQueryable.Select("new(it[""curr""] as Curry)")
Dim tbl As DataTable = query
Ive tried:
Dim query As IEnumerable(Of DataRow) = tbl.AsEnumerable.AsQueryable.Select("new(it[""curr""] as Curry)").Cast(Of DataRow)()
Dim tbl1 As DataTable = query.CopyToDataTable
but that gives me:
Unable to cast object of type 'DynamicClass1' to type 'System.Data.DataRow'.
Public Shared Function ConvertIEnumerableToDataTableFromProperties(Of T)(ByVal list As IEnumerable(Of T)) As DataTable
Dim table As New DataTable()
Dim fields() As PropertyInfo = GetType(T).GetProperties()
For Each field As PropertyInfo In fields
table.Columns.Add(field.Name, field.PropertyType)
Next
For Each item As T In list
Dim row As DataRow = table.NewRow()
For Each field As PropertyInfo In fields
row(field.Name) = field.GetValue(item)
Next
table.Rows.Add(row)
Next
Return table
End Function
I am building a predicate in VB.net using the PredicateBuilder class from the LinqKit library.
My datasource is a manually constructed datatable.
All the examples I've found show folks creating the predicate and then passing that predicate as an argument to the Where() method on the datatable.AsEnumerable().
But intellisense is telling me that the Where() method takes a paremeter of type "System.Func", but the type returned by PredicateBuilder is "System.Linq.Expressions.Expression(Of Func(Of T, Boolean))"
What am I missing?
Example:
Dim ds As DataTable = getData()
Dim tmp As IEnumerable(Of DataRow) = New DataTable().AsEnumerable()
' CREATE DYNAMIC LINQ WHERE CLAUSE
Dim predicate As System.Linq.Expressions.Expression(Of Func(Of DataRow, Boolean)) = PredicateBuilder.True(Of DataRow)()
If cbHPMS_ShowRequired.Checked Then
predicate = predicate.And(Function(x As DataRow) x("RECORD_TYPE") = "REQUIRED")
End If
If cbHPMS_ShowOptional.Checked Then
predicate = predicate.And(Function(x As DataRow) x("RECORD_TYPE") = "OPTIONAL")
End If
If cbHPMS_EmptyRecord.Checked Then
predicate = predicate.And(Function(x As DataRow) x("RECORD_STATUS") = "EMPTY")
End If
If cbHPMS_PartialRecord.Checked Then
predicate = predicate.And(Function(x As DataRow) x("RECORD_STATUS") = "PARTIAL")
End If
If cbHPMS_CompletedRecord.Checked Then
predicate = predicate.And(Function(x As DataRow) x("RECORD_STATUS") = "COMPLETE")
End If
If Not String.IsNullOrEmpty(ddHPMS_RoadName.SelectedValue) And Not ddHPMS_RoadName.SelectedValue.Equals("Select") Then
predicate = predicate.And(Function(x As DataRow) x("RoadName") = ddHPMS_RoadName.SelectedValue)
End If
tmp = ds.AsEnumerable().Where(predicate)
I have not used LinqKit but would think it would be like
tmp = ds.AsEnumerable().Where(predicate.Compile())