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Creating a DataTable From a Query (LINQ to DataSet)

Data binding is a common use of DataTable object. The CopyToDataTable method takes the results of a query and copies the data into a DataTable, which can then be used for data binding. When the data operations have been performed, the new DataTable is merged back into the source DataTable.

The CopyToDataTable method uses the following process to create a DataTable from a query:

  1. The CopyToDataTable method clones a DataTable from the source table (a DataTable object that implements the IQueryable(Of T) interface). The IEnumerable source has generally originated from a LINQ to DataSet expression or method query.

  2. The schema of the cloned DataTable is built from the columns of the first enumerated DataRow object in the source table and the name of the cloned table is the name of the source table with the word "query" appended to it.

  3. For each row in the source table, the content of the row is copied into a new DataRow object, which is then inserted into the cloned table. The RowState and RowError properties are preserved across the copy operation. An ArgumentException is thrown if the DataRow objects in the source are from different tables.

  4. The cloned DataTable is returned after all DataRow objects in the input queryable table have been copied. If the source sequence does not contain any DataRow objects, the method returns an empty DataTable.

Note that calling the CopyToDataTable method will cause the query bound to the source table to execute.

When the CopyToDataTable method encounters either a null reference or nullable value type in a row in the source table, it replaces the value with Value. This way, null values are handled correctly in the returned DataTable.

Note: The CopyToDataTable method accepts as input a query that can return rows from multiple DataTable or DataSet objects. The CopyToDataTable method will copy the data but not the properties from the source DataTable or DataSet objects to the returned DataTable. You will need to explicitly set the properties on the returned DataTable, such as Locale and TableName.

The following example queries the SalesOrderHeader table for orders after August 8, 2001 and uses the CopyToDataTable method to create a DataTable from that query. The DataTable is then bound to a BindingSource, which acts as proxy for a DataGridView.


' Bind the System.Windows.Forms.DataGridView object
' to the System.Windows.Forms.BindingSource object.
dataGridView.DataSource = bindingSource

' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)

Dim orders As DataTable = ds.Tables("SalesOrderHeader")

' Query the SalesOrderHeader table for orders placed 
'  after August 8, 2001.
Dim query = _
    From order In orders.AsEnumerable() _
    Where order.Field(Of DateTime)("OrderDate") > New DateTime(2001, 8, 1) _
    Select order

' Create a table from the query.
Dim boundTable As DataTable = query.CopyToDataTable()

' Bind the table to a System.Windows.Forms.BindingSource object, 
' which acts as a proxy for a System.Windows.Forms.DataGridView object.
bindingSource.DataSource = boundTable


The existing CopyToDataTable methods only operate on an IEnumerable(Of T) source where the generic parameter T is of type DataRow. Although this is useful, it does not allow tables to be created from a sequence of scalar types, from queries that return anonymous types, or from queries that perform table joins. For an example of how to implement two custom CopyToDataTable methods that load a table from a sequence of scalar or anonymous types, see How to: Implement CopyToDataTable<T> Where the Generic Type T Is Not a DataRows.

The examples in this section use the following custom types:


Public Class Item
    Private _Id As Int32
    Private _Price As Double
    Private _Genre As String

    Public Property Id() As Int32
        Get
            Return Id
        End Get
        Set(ByVal value As Int32)
            _Id = value
        End Set
    End Property

    Public Property Price() As Double
        Get
            Return _Price
        End Get
        Set(ByVal value As Double)
            _Price = value
        End Set
    End Property

    Public Property Genre() As String
        Get
            Return _Genre
        End Get
        Set(ByVal value As String)
            _Genre = value
        End Set
    End Property

End Class
Public Class Book
    Inherits Item
    Private _Author As String
    Public Property Author() As String
        Get
            Return _Author
        End Get
        Set(ByVal value As String)
            _Author = value
        End Set
    End Property
End Class

Public Class Movie
    Inherits Item
    Private _Director As String
    Public Property Director() As String
        Get
            Return _Director
        End Get
        Set(ByVal value As String)
            _Director = value
        End Set
    End Property

End Class


Example

This example performs a join over the SalesOrderHeader and SalesOrderDetail tables to get online orders from the month of August and creates a table from the query.


' Fill the DataSet.
Dim ds As New DataSet()
ds.Locale = CultureInfo.InvariantCulture
' See the FillDataSet method in the Loading Data Into a DataSet topic.
FillDataSet(ds)

Dim orders As DataTable = ds.Tables("SalesOrderHeader")
Dim details As DataTable = ds.Tables("SalesOrderDetail")


Dim query = _
    From order In orders.AsEnumerable() _
    Join detail In details.AsEnumerable() _
    On order.Field(Of Integer)("SalesOrderID") Equals _
            detail.Field(Of Integer)("SalesOrderID") _
    Where order.Field(Of Boolean)("OnlineOrderFlag") = True And _
            order.Field(Of DateTime)("OrderDate").Month = 8 _
    Select New With _
    { _
        .SalesOrderID = order.Field(Of Integer)("SalesOrderID"), _
        .SalesOrderDetailID = detail.Field(Of Integer)("SalesOrderDetailID"), _
        .OrderDate = order.Field(Of DateTime)("OrderDate"), _
        .ProductID = detail.Field(Of Integer)("ProductID") _
    }

Dim table As DataTable = query.CopyToDataTable()


Example

The following example queries a collection for items of price greater than $9.99 and creates a table from the query results.


Dim book1 As New Book()
book1.Id = 1
book1.Price = 13.5
book1.Genre = "Comedy"
book1.Author = "Gustavo Achong"

Dim book2 As New Book
book2.Id = 2
book2.Price = 8.5
book2.Genre = "Drama"
book2.Author = "Jessie Zeng"

Dim movie1 As New Movie
movie1.Id = 1
movie1.Price = 22.99
movie1.Genre = "Comedy"
movie1.Director = "Marissa Barnes"

Dim movie2 As New Movie
movie2.Id = 1
movie2.Price = 13.4
movie2.Genre = "Action"
movie2.Director = "Emmanuel Fernandez"

Dim items(3) As Item
items(0) = book1
items(1) = book2
items(2) = movie1
items(3) = movie2

' Query for items with price greater than 9.99.
Dim query = From i In items _
            Where i.Price > 9.99 _
            Order By i.Price _
            Select New With {i.Price, i.Genre}

Dim table As DataTable
table = query.CopyToDataTable()


Example

The following example queries a collection for items of price greater than 9.99 and projects the results. The returned sequence of anonymous types is loaded into an existing table.


Dim book1 As New Book()
book1.Id = 1
book1.Price = 13.5
book1.Genre = "Comedy"
book1.Author = "Gustavo Achong"

Dim book2 As New Book
book2.Id = 2
book2.Price = 8.5
book2.Genre = "Drama"
book2.Author = "Jessie Zeng"

Dim movie1 As New Movie
movie1.Id = 1
movie1.Price = 22.99
movie1.Genre = "Comedy"
movie1.Director = "Marissa Barnes"

Dim movie2 As New Movie
movie2.Id = 1
movie2.Price = 13.4
movie2.Genre = "Action"
movie2.Director = "Emmanuel Fernandez"

Dim items(3) As Item
items(0) = book1
items(1) = book2
items(2) = movie1
items(3) = movie2

' Create a table with a schema that matches that of the query results.            
Dim table As DataTable = New DataTable()
table.Columns.Add("Price", GetType(Integer))
table.Columns.Add("Genre", GetType(String))

' Query for items with price greater than 9.99.
Dim query = From i In items _
            Where i.Price > 9.99 _
            Order By i.Price _
            Select New With {i.Price, i.Genre}

query.CopyToDataTable(table, LoadOption.PreserveChanges)


Example

The following example queries a collection for items of price greater than $9.99 and projects the results. The returned sequence of anonymous types is loaded into an existing table. The table schema is automatically expanded because the Book and Movies types are derived from the Item type.


Dim book1 As New Book()
book1.Id = 1
book1.Price = 13.5
book1.Genre = "Comedy"
book1.Author = "Gustavo Achong"

Dim book2 As New Book
book2.Id = 2
book2.Price = 8.5
book2.Genre = "Drama"
book2.Author = "Jessie Zeng"

Dim movie1 As New Movie
movie1.Id = 1
movie1.Price = 22.99
movie1.Genre = "Comedy"
movie1.Director = "Marissa Barnes"

Dim movie2 As New Movie
movie2.Id = 1
movie2.Price = 13.4
movie2.Genre = "Action"
movie2.Director = "Emmanuel Fernandez"

Dim items(3) As Item
items(0) = book1
items(1) = book2
items(2) = movie1
items(3) = movie2

' Load into an existing DataTable, expand the schema and
' autogenerate a new Id.
Dim table As DataTable = New DataTable()
Dim dc As DataColumn = table.Columns.Add("NewId", GetType(Integer))
dc.AutoIncrement = True
table.Columns.Add("ExtraColumn", GetType(String))

Dim query = From i In items _
            Where i.Price > 9.99 _
            Order By i.Price _
            Select New With {i.Price, i.Genre}

query.CopyToDataTable(table, LoadOption.PreserveChanges)


Example

The following example queries a collection for items of price greater than $9.99 and returns a sequence of Double, which is loaded into a new table.


Dim book1 As New Book()
book1.Id = 1
book1.Price = 13.5
book1.Genre = "Comedy"
book1.Author = "Gustavo Achong"

Dim book2 As New Book
book2.Id = 2
book2.Price = 8.5
book2.Genre = "Drama"
book2.Author = "Jessie Zeng"

Dim movie1 As New Movie
movie1.Id = 1
movie1.Price = 22.99
movie1.Genre = "Comedy"
movie1.Director = "Marissa Barnes"

Dim movie2 As New Movie
movie2.Id = 1
movie2.Price = 13.4
movie2.Genre = "Action"
movie2.Director = "Emmanuel Fernandez"

Dim items(3) As Item
items(0) = book1
items(1) = book2
items(2) = movie1
items(3) = movie2

Dim query = From i In items _
            Where i.Price > 9.99 _
            Order By i.Price _
            Select i.Price

Dim table As DataTable
table = query.CopyToDataTable()


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