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How to: Implement CopyToDataTable<T> Where the Generic Type T Is Not a DataRow
Imports System
Imports System.Data
Imports System.Runtime.CompilerServices
Imports System.Reflection
Imports System.Collections.Generic
''' <summary>
''' How to: Implement CopyToDataTable<T> Where the Generic Type T Is Not a DataRow
''' </summary>
''' <remarks>
''' https://msdn.microsoft.com/en-us/library/bb669096.aspx
''' </remarks>
Public Module CustomLINQtoDataSetMethods
<Extension()> _
Public Function CopyToDataTable(Of T)(ByVal source As IEnumerable(Of T)) As DataTable
Return New ObjectShredder(Of T)().Shred(source, Nothing, Nothing)
End Function
<Extension()> _
Public Function CopyToDataTable(Of T)(ByVal source As IEnumerable(Of T), ByVal table As DataTable, ByVal options As LoadOption?) As DataTable
Return New ObjectShredder(Of T)().Shred(source, table, options)
End Function
End Module
Public Class ObjectShredder(Of T)
' Fields
Private _fi As FieldInfo()
Private _ordinalMap As Dictionary(Of String, Integer)
Private _pi As PropertyInfo()
Private _type As Type
' Constructor
Public Sub New()
Me._type = GetType(T)
Me._fi = Me._type.GetFields
Me._pi = Me._type.GetProperties
Me._ordinalMap = New Dictionary(Of String, Integer)
End Sub
Public Function ShredObject(ByVal table As DataTable, ByVal instance As T) As Object()
Dim fi As FieldInfo() = Me._fi
Dim pi As PropertyInfo() = Me._pi
If (Not instance.GetType Is GetType(T)) Then
' If the instance is derived from T, extend the table schema
' and get the properties and fields.
Me.ExtendTable(table, instance.GetType)
fi = instance.GetType.GetFields
pi = instance.GetType.GetProperties
End If
' Add the property and field values of the instance to an array.
Dim values As Object() = New Object(table.Columns.Count - 1) {}
Dim f As FieldInfo
For Each f In fi
values(Me._ordinalMap.Item(f.Name)) = f.GetValue(instance)
Next
Dim p As PropertyInfo
For Each p In pi
values(Me._ordinalMap.Item(p.Name)) = p.GetValue(instance, Nothing)
Next
' Return the property and field values of the instance.
Return values
End Function
''' <summary>
''' Loads a DataTable from a sequence of objects.
''' </summary>
''' <param name="source">The sequence of objects to load into the DataTable.</param>
''' <param name="table">
''' The input table. The schema of the table must match that
''' the type T. If the table is null, a new table is created
''' with a schema created from the public properties and fields
''' of the type T.
''' </param>
''' <param name="options">
''' Specifies how values from the source sequence will be applied to
''' existing rows in the table.
''' </param>
''' <returns>A DataTable created from the source sequence</returns>
''' <remarks></remarks>
Public Function Shred(ByVal source As IEnumerable(Of T), ByVal table As DataTable, ByVal options As LoadOption?) As DataTable
' Load the table from the scalar sequence if T is a primitive type.
If GetType(T).IsPrimitive Then
Return Me.ShredPrimitive(source, table, options)
End If
' Create a new table if the input table is null.
If (table Is Nothing) Then
table = New DataTable(GetType(T).Name)
End If
' Initialize the ordinal map and extend the table schema based on type T.
table = Me.ExtendTable(table, GetType(T))
' Enumerate the source sequence and load the object values into rows.
table.BeginLoadData()
Using e As IEnumerator(Of T) = source.GetEnumerator
Do While e.MoveNext
If options.HasValue Then
table.LoadDataRow(Me.ShredObject(table, e.Current), options.Value)
Else
table.LoadDataRow(Me.ShredObject(table, e.Current), True)
End If
Loop
End Using
table.EndLoadData()
' Return the table.
Return table
End Function
Public Function ShredPrimitive(ByVal source As IEnumerable(Of T),
ByVal table As DataTable,
ByVal options As LoadOption?) As DataTable
' Create a new table if the input table is null.
If (table Is Nothing) Then
table = New DataTable(GetType(T).Name)
End If
If Not table.Columns.Contains("Value") Then
table.Columns.Add("Value", GetType(T))
End If
' Enumerate the source sequence and load the scalar values into rows.
table.BeginLoadData()
Using e As IEnumerator(Of T) = source.GetEnumerator
Dim values As Object() = New Object(table.Columns.Count - 1) {}
Do While e.MoveNext
values(table.Columns.Item("Value").Ordinal) = e.Current
If options.HasValue Then
table.LoadDataRow(values, options.Value)
Else
table.LoadDataRow(values, True)
End If
Loop
End Using
table.EndLoadData()
' Return the table.
Return table
End Function
''' <summary>
''' Extend the table schema if the input table was null or if the value in the sequence is derived from type T
''' </summary>
Public Function ExtendTable(ByVal table As DataTable, ByVal type As Type) As DataTable
Dim f As FieldInfo
Dim p As PropertyInfo
For Each f In type.GetFields
If Not Me._ordinalMap.ContainsKey(f.Name) Then
Dim dc As DataColumn
' Add the field as a column in the table if it doesn't exist already.
dc = If(table.Columns.Contains(f.Name),
table.Columns.Item(f.Name),
table.Columns.Add(f.Name, f.FieldType))
' Add the field to the ordinal map.
Me._ordinalMap.Add(f.Name, dc.Ordinal)
End If
Next
For Each p In type.GetProperties
If Not Me._ordinalMap.ContainsKey(p.Name) Then
' Add the property as a column in the table if it doesn't exist already.
Dim dc As DataColumn
dc = If(table.Columns.Contains(p.Name),
table.Columns.Item(p.Name),
table.Columns.Add(p.Name, p.PropertyType))
' Add the property to the ordinal map.
Me._ordinalMap.Add(p.Name, dc.Ordinal)
End If
Next
' Return the table.
Return table
End Function
End Class