I've been working on a project which has a Function of reading Data from a DataTable and returning it as a list. I made specific statements over some rows to get the data I want.
Little problem is, my entity "Number" is declared As an Integer and in the DataTable I do have some String values which leads the function to crash. Do any of you guys has an Idea about how I can check which Data Type the row "Number" has and if it's not an Integer to just leave it out?
My function looks like this:
Public Function LiefereAlleRechte(ByVal dt As DataTable) As ICollection(Of Recht) Implements IBenutzerInfoServiceUtil.LiefereAlleRechte
If dt Is Nothing Then
Throw New ArgumentNullException("DataTable can't be empty", "dt")
End If
Dim query = From dr As DataRow In dt.DefaultView.ToTable(True, "Name", "Number")
Dim coll As ICollection(Of Recht) = New List(Of Recht)
For Each row In query
Dim recht As Recht = New Recht()
With recht
.Name = row.Item("Name")
.Nummer = row.Item("Number")
coll.Add(recht)
End With
Next
Return coll
End Function
Thanks for any help!
Related
All the examples I have found of complex grouping of DataTable results that use linq query commands look to have no problems getting an IEnumerable(Of DataRow) object as the result.
However I seem to only get a AnonymousType Enumerator return that I cannot cast to DataTable.
I have workarounds, but would prefer to convert the results to a DataTable, as it looks possible and I may be doing something wrong.
It's a simple table with Many ClientID and ClientName columns and other columns with login timestamps.
Dim dtMatrix As DataTable = New DataTable()
... (populate DataTable)
Dim qClients = From row In dtMatrix
Group row By client = New With {Key .ClientID = row("ClientID"), Key .ClientName = row("ClientName")} Into Group
Select New With {Key .ClientID = client.ClientID, Key .ClientName = client.ClientName}
This returns the generic Enumerator result, however
Dim qClients As IEnumerable(Of DataRow) = From row In dtMatrix
Group row By client = New With {Key .ClientID = row("ClientID"), Key .ClientName = row("ClientName")} Into Group
Select New With {Key .ClientID = client.ClientID, Key .ClientName = client.ClientName}
Throws an exception
Unable to cast object of type... to type
'System.Collections.Generic.IEnumerable`1[System.Data.DataRow]'.
I will be happy to paste the whole error message if it will add more clarity.
My base assumption is that the DataTable should allow the cast to occur inherently as it is the object being queried. However this does not seem to be the case. Have I constructed my query incorrectly? (Framework 4.6.2)
You can use OfType on the Rows property of the DataTable:
Dim dtMatrix As DataTable = New DataTable()
'' Populate code goes here...
Dim dtRows As IEnumerable(Of DataRow) = dtMatrix.Rows.OfType(Of DataRow)()
The Rows property returns a DataRowCollection, that implements (through inheritance) the IEnumerable interface but not the IEnumerable(Of T) interface, that's why you can't use most of linq over it directly.
The following extension uses Reflection to create a new DataTable and create DataColumns in it that match the properties and fields of the type passed in. In general, if you are creating anonymous types in LINQ, you can't just convert to a DataRow which must be tied to a DataTable which must already have matching columns. I went ahead and wrote a second extension to DataTable that adds an IEnumerable<T> with matching field/property names to it.
Public Module Ext
<Extension()>
Public Function GetValue(member As MemberInfo, srcObject As Object) As Object
If TypeOf member Is FieldInfo Then
Return DirectCast(member, FieldInfo).GetValue(srcObject)
ElseIf TypeOf member Is PropertyInfo Then
Return DirectCast(member, PropertyInfo).GetValue(srcObject)
Else
Throw New ArgumentException("MemberInfo must be of type FieldInfo or PropertyInfo", Nameof(member))
End If
End Function
<Extension()>
Public Function GetMemberType(member As MemberInfo) As Type
If TypeOf member Is FieldInfo Then
Return DirectCast(member, FieldInfo).FieldType
ElseIf TypeOf member Is PropertyInfo Then
Return DirectCast(member, PropertyInfo).PropertyType
ElseIf TypeOf member Is EventInfo Then
Return DirectCast(member, EventInfo).EventHandlerType
Else
Throw New ArgumentException("MemberInfo must be of type FieldInfo, PropertyInfo or EventInfo", Nameof(member))
End If
End Function
<Extension()>
Public Function ToDataTable(Of T)(rows As IEnumerable(Of T)) As DataTable
Dim dt = New DataTable
If (rows.Any()) Then
Dim rowType = rows.First().GetType()
Dim memberInfos = rowType.GetProperties.Cast(Of MemberInfo)().Concat(rowType.GetFields).ToArray()
For Each info In memberInfos
dt.Columns.Add(New DataColumn(info.Name, info.GetMemberType()))
Next
For Each r In rows
dt.Rows.Add(memberInfos.Select(Function (i) i.GetValue(r)).ToArray())
Next
End If
Return dt
End Function
<Extension()>
Public Function AddObjects(Of T)(dt As DataTable, rows As IEnumerable(Of T))
If (rows.Any()) Then
Dim rowType = rows.First().GetType()
Dim memberInfos = rowType.GetProperties().Cast(Of MemberInfo)().Concat(rowType.GetFields()).ToArray()
For Each r In rows
Dim newRow = dt.NewRow()
For Each memberInfo In memberInfos
newRow(memberInfo.Name) = memberInfo.GetValue(r)
Next
dt.Rows.Add(newRow)
Next
End If
Return dt
End Function
End Module
Note that I write in C# and translated this from my C# extension. It is untested but compiles.
Using the extension, you should be able to get a DataTable from your qClients by:
Dim dtClients = qClients.ToDataTable()
I am using the following function to retrieve records from a database and convert the records to a collection of strongly typed objects.
Private Function GetPlantSettingsFiltered(parameters As Dictionary(Of String, Object), queryCondition As String) As PlantSettings
Dim query As String
query = " SELECT * FROM Plant_Settings " _
+ queryCondition
Dim settings As New PlantSettings
Dim table As DataTable = GetQueryResults(parameters, query, GetConnectionString("WeighScaleDB"))
If table Is Nothing Then
Return settings
End If
For Each row As DataRow In table.Rows
settings.Add(New PlantSetting With {
.Setting_ID = ConvertByteArrayToString(TryCast(row("Setting_ID"), Byte())),
.Plant_ID = ConvertByteArrayToString(TryCast(row("Plant_ID"), Byte())),
.Value = row("Setting_Value").ToString(),
.Comments = row("Setting_Comments").ToString()
})
Next
Return settings
End Function
I would like to create a generic version of this function that would work for any of my objects without me creating this function for each object.
For example, if the caller could specify the type, then some other details, the function would return a collection of that type.
Private Function GetObjects(Of T)(parameters As Dictionary(Of String, Object), query As String) As WSAEntityCollection(Of T)
Dim objectCollection As New WSAEntityCollection(Of T)
Dim table As DataTable = GetQueryResults(parameters, query, GetConnectionString("WeighScaleDB"))
If table Is Nothing Then
Return objectCollection
End If
For Each row As DataRow In table.Rows
' Here is my problem
objectCollection.Add(New T With {})
Next
Return objectCollection
End Function
My current problem with this new function is that I do not know how to dynamically match the column names with the parameters of the generic object. Any ideas on how this could be done?
I have read some threads about this "error" but I can't figure out how to solve my problem.
I have a class that looks something like this:
Public Class Person
Public Property Name As String
Public Property PhoneNumber As string
Public Property Age As Integer
Public sub New(ByVal Values As String())
Me.Name = Values(0)
Me.PhoneNumber = Values(1)
Me.Age = Convert.ToInt32(Values(2))
End Sub
End Class
I get my data from a semicolon separated file, and i create a list of Person objects by looping this file and split on semicolon. Like this
Dim PersonsList As New List(Of Person)
For Each line in textfile..........
PersonsList.Add(New Person(line.Split(";")))
Next
When the list is complete, I tell my DataGridView that DataSource is PersonsList.
This works like a charm, but I'm not able to sort the columns.
I found this post amongst many (where the class values are not properties, which mine are) and tried that converting function which did'nt really work in my case. The right amount of rows were created, but all of the columns were blank.
What am I missing?
If you use a datatable as the data source, column sorting is automatically enabled and you can sort the data by any column:
Dim dt As New DataTable
dt.Columns.AddRange(
{
New DataColumn("Name"),
New DataColumn("Phone"),
New DataColumn("Age")
})
For Each s As String In IO.File.ReadAllLines("textfile1.txt")
Dim temprow As DataRow = dt.NewRow
temprow.ItemArray = s.Split(";"c)
dt.Rows.Add(temprow)
Next
DataGridView1.DataSource = dt
Hi i am trying to sum all my datatable values to one row. but i retrieve a InvalidCastException:
Failed to convert an object of
typeWhereSelectEnumerableIterator2[System.Linq.IGrouping2[System.Object,System.Data.DataRow],VB$AnonymousType_0`4[System.Object,System.Double,System.Decimal,System.Decimal]]
to type System.Data.DataTable.
SQL Datatypes:
NAME_AGE string
LON money
sal_tjformon money
sal_sjuklon money
Private Function GroupByName(dataTable As DataTable) As DataTable
Dim result = dataTable.AsEnumerable().GroupBy(
Function(row) row.Item("NAME_AGE")).Select(Function(group) New With {
.Grp = group.Key,
.LON = group.Sum(Function(r) Decimal.Parse(r.Item("LON"))),
.sal_tjformon = group.Sum(Function(r) Decimal.Parse(r.Item("sal_tjformon"))),
.sal_sjuklon = group.Sum(Function(r) Decimal.Parse(r.Item("sal_sjuklon")))
})
Return result
The LINQ statement returns an IEnumerable(Of <anonymous_type>). There are two problems with this. First of all, your function returns a DataTable, which your object definitely is not. Secondly of all, you can't return an anonymous type from a function call.
If you want to return the select result, you have to create an explicit type (a class) and return the IEnumerable(Of MyType), like in the code below. I strongly advice to set an explicit type to the Grp property (like String?).
Class GroupNameAgeResult
Public Property Grp As Object
Public Property LON As Decimal
Public Property sal_tjformon As Decimal
Public Property sal_sjuklon As Decimal
End Class
Private Function GroupByName(dataTable As DataTable) As IEnumerable(Of GroupNameAgeResult)
Dim result = dataTable.AsEnumerable().GroupBy(Function(row) row.Item("NAME_AGE")) _
.Select(Function(grp) New GroupNameAgeResult() With
{.Grp = grp.Key,
.LON = grp.Sum(Function(r) Decimal.Parse(r.Item("LON").ToString)),
.sal_tjformon = grp.Sum(Function(r) Decimal.Parse(r.Item("sal_tjformon").ToString)),
.sal_sjuklon = grp.Sum(Function(r) Decimal.Parse(r.Item("sal_sjuklon").ToString))})
Return result
End Function
If you want to return a DataTable, you can define this, loop over the groups and add a row. You can return afterwards the result. See example code below.
Private Function GroupByName(dataTable As DataTable) As DataTable
Dim result As New DataTable()
result.Columns.Add("Grp", GetType(Object))
result.Columns.Add("LON", GetType(Decimal))
result.Columns.Add("sal_tjformon", GetType(Decimal))
result.Columns.Add("sal_sjuklon", GetType(Decimal))
For Each grp In dataTable.AsEnumerable().GroupBy(Function(row) row.Item("NAME_AGE"))
Dim row As DataRow = result.NewRow()
row.Item("Grp") = grp.Key
row.Item("LON") = grp.Sum(Function(r) Decimal.Parse(r.Item("LON").ToString))
row.Item("sal_tjformon") = grp.Sum(Function(r) Decimal.Parse(r.Item("sal_tjformon").ToString))
row.Item("sal_sjuklon") = grp.Sum(Function(r) Decimal.Parse(r.Item("sal_sjuklon").ToString))
result.Rows.Add(row)
Next
Return result
End Function
Last but not least. I strongly advice you to turn on "Option strict" (you can set this in the project properties -> Compile). You'll notice many more (possible) errors with your code (even the small function from this question).
Today I am needing to write LINQ queries in VB.net to a database table, but am new to SQL/LINQ. This function below is meant to fill a list of strings with all of the possible "Questions" in the database table that match the QuestionType.
However, I only want to select one single column, the QuestionText column, and not all of the data, whenever I have a match.
Public Shared Function RetrieveQuestions(ByVal QuestionType) As List(Of String)
Dim db As New DBDataContext()
db.CommandTimeout = 300
Dim ListOfQuestions As List(Of String) = New List(Of String)
While True
Dim questionList As List(Of Question) = db.Questions.ToList
Dim question As List(Of String) = (From q As Question In questionList Where q.FormType = QuestionType Select q.QuestionText).ToList
Dim i As List(Of String) = question
If (question IsNot Nothing) Then
ListOfQuestions(ListOfQuestions.Count) = i.QuestionText //ERROR
Else
Exit While
End If
End While
Return ListOfQuestions
End Function
In the function above i am encountering an error when trying to update my list with the new QuestionText. "QuestionText is not a member of System.Collections.Generic.List(Of String)". QuestionText is defined as a varchar in my SQL database, so I know that it is definitely a string. I am not trying to set QuestionText to a list of strings, but rather add it to the end of a list of strings.
Direct answer: you'd need to put the whole If (question IsNot Nothing) Then block in a loop like For Each. As the compiler correctly informs - the i variable holds the whole list, not one of its items. Perhaps you forgot you left the LINQ query?
A better solution: I believe you could just use AndAlso q.QuestionText IsNot Nothing - it spares you the need to allocate a new list and to fill it one by one - the following code should do the trick.
Public Shared Function RetrieveQuestions(ByVal QuestionType) As List(Of String)
Dim db As New DBDataContext()
db.CommandTimeout = 300
Dim ListOfQuestions As List(Of String) = (
From q As Question In db.Questions.ToList
Where
q.FormType = QuestionType
AndAlso q.QuestionText IsNot Nothing
Select q.QuestionText
).ToList
Return ListOfQuestions
End Function