Creazione di un oggetto DataTable da una query (LINQ to DataSet)Creating a DataTable From a Query (LINQ to DataSet)

L'associazione dati è un utilizzo comune dell'oggetto DataTable.Data binding is a common use of DataTable object. Il metodo CopyToDataTable copia i dati dei risultati di una query in un oggetto DataTable che può essere quindi usato per il data binding.The CopyToDataTable method takes the results of a query and copies the data into a DataTable, which can then be used for data binding. Dopo l'esecuzione delle operazioni sui dati, il nuovo oggetto DataTable viene nuovamente unito nell'oggetto DataTable di origine.When the data operations have been performed, the new DataTable is merged back into the source DataTable.

Il metodo CopyToDataTable usa il processo seguente per creare DataTable da una query.The CopyToDataTable method uses the following process to create a DataTable from a query:

  1. Il metodo CopyToDataTable duplica un oggetto DataTable della tabella di origine, ovvero un oggetto DataTable che implementa l'interfaccia IQueryable<T>.The CopyToDataTable method clones a DataTable from the source table (a DataTable object that implements the IQueryable<T> interface). Il IEnumerable origine viene solitamente generato da LINQ a DataSet espressione o metodo di query.The IEnumerable source has generally originated from a LINQ to DataSet expression or method query.

  2. Lo schema dell'oggetto DataTable duplicato viene compilato dalle colonne del primo oggetto DataRow enumerato nella tabella di origine, mentre il nome della tabella duplicata corrisponde al nome della tabella di origine con l'aggiunta del termine "query" alla fine.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. Il contenuto di ogni riga della tabella di origine viene copiato in un nuovo oggetto DataRow, che viene quindi inserito nella tabella duplicata.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. Le proprietà RowState e RowError vengono mantenuta durante l'operazione di copia.The RowState and RowError properties are preserved across the copy operation. Se gli oggetti ArgumentException nell'origine provengono da tabelle diverse, viene generata un'eccezione DataRow.An ArgumentException is thrown if the DataRow objects in the source are from different tables.

  4. L'oggetto DataTable duplicato viene restituito dopo che sono stati copiati tutti gli oggetti DataRow presenti nella tabella di input sottoposta a query.The cloned DataTable is returned after all DataRow objects in the input queryable table have been copied. Se la sequenza di origine non contiene oggetti DataRow, il metodo restituisce un oggetto DataTable vuoto.If the source sequence does not contain any DataRow objects, the method returns an empty DataTable.

Si noti che la chiamata al metodo CopyToDataTable genererà l'esecuzione della query associata alla tabella di origine.Note that calling the CopyToDataTable method will cause the query bound to the source table to execute.

Quando il metodo CopyToDataTable rileva un riferimento Null o un tipo di valore nullable in una riga della tabella di origine, sostituisce il valore con Value.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. I valori Null vengono gestiti correttamente nell'oggetto DataTable restituito.This way, null values are handled correctly in the returned DataTable.

Nota: Il CopyToDataTable metodo accetta come input una query che può restituire righe da più DataTable o DataSet oggetti.Note: The CopyToDataTable method accepts as input a query that can return rows from multiple DataTable or DataSet objects. Il metodo CopyToDataTable consente di copiare i dati ma non le proprietà dagli oggetti DataTable o DataSet di origine nell'oggetto DataTable restituito.The CopyToDataTable method will copy the data but not the properties from the source DataTable or DataSet objects to the returned DataTable. È necessario impostare in modo esplicito le proprietà nell'oggetto DataTable restituito, ad esempio Locale e TableName.You will need to explicitly set the properties on the returned DataTable, such as Locale and TableName.

Nell'esempio seguente viene eseguita una query sulla tabella SalesOrderHeader per individuare gli ordini effettuati dopo l'8 agosto 2001 e viene usato il metodo CopyToDataTable per creare un oggetto DataTable dalla query.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. DataTable viene quindi associato a BindingSource, che funge da proxy per DataGridView.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.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable orders = ds.Tables["SalesOrderHeader"];

// Query the SalesOrderHeader table for orders placed 
// after August 8, 2001.
IEnumerable<DataRow> query =
    from order in orders.AsEnumerable()
    where order.Field<DateTime>("OrderDate") > new DateTime(2001, 8, 1)
    select order;

// Create a table from the query.
DataTable boundTable = query.CopyToDataTable<DataRow>();

// 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;
' 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

Creazione di un CopyToDataTable personalizzato<T > (metodo)Creating a Custom CopyToDataTable<T> Method

I metodi CopyToDataTable esistenti funzionano solo su un'origine IEnumerable<T> in cui il parametro generico T è di tipo DataRow.The existing CopyToDataTable methods only operate on an IEnumerable<T> source where the generic parameter T is of type DataRow. Sebbene sia utile, questa funzionalità non consente di creare tabelle da una sequenza di tipi scalari, da query che restituiscono tipi anonimi o da query che eseguono join di tabelle.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. Per un esempio di come implementare due custom CopyToDataTable metodi di caricamento di una tabella da una sequenza di tipi scalari o anonimi, vedere come: Implementare CopyToDataTable<T > in cui il tipo generico T non è un DataRows.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.

Per gli esempi di questa sezione vengono usati i tipi personalizzati seguenti:The examples in this section use the following custom types:

public class Item
{
    public int Id { get; set; }
    public double Price { get; set; }
    public string Genre { get; set; }
}

public class Book : Item
{
    public string Author { get; set; }
}

public class Movie : Item
{
    public string Director { get; set; }
}
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

EsempioExample

In questo esempio viene eseguito un join sulle tabelle SalesOrderHeader e SalesOrderDetail per ottenere gli ordini effettuati online dal mese di agosto e viene creata una tabella dalla query.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.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable orders = ds.Tables["SalesOrderHeader"];
DataTable details = ds.Tables["SalesOrderDetail"];

var query =
    from order in orders.AsEnumerable()
    join detail in details.AsEnumerable()
    on order.Field<int>("SalesOrderID") equals
        detail.Field<int>("SalesOrderID")
    where order.Field<bool>("OnlineOrderFlag") == true
    && order.Field<DateTime>("OrderDate").Month == 8
    select new
    {
        SalesOrderID =
            order.Field<int>("SalesOrderID"),
        SalesOrderDetailID =
            detail.Field<int>("SalesOrderDetailID"),
        OrderDate =
            order.Field<DateTime>("OrderDate"),
        ProductID =
            detail.Field<int>("ProductID")
    };

DataTable orderTable = query.CopyToDataTable(); 
' 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()

EsempioExample

Nell'esempio seguente viene eseguita una query su una raccolta per ottenere gli articoli con prezzo maggiore di 9,99 $ e viene creata una tabella dai risultati della query.The following example queries a collection for items of price greater than $9.99 and creates a table from the query results.

// Create a sequence. 
Item[] items = new Item[] 
{ new Book{Id = 1, Price = 13.50, Genre = "Comedy", Author = "Gustavo Achong"}, 
  new Book{Id = 2, Price = 8.50, Genre = "Drama", Author = "Jessie Zeng"},
  new Movie{Id = 1, Price = 22.99, Genre = "Comedy", Director = "Marissa Barnes"},
  new Movie{Id = 1, Price = 13.40, Genre = "Action", Director = "Emmanuel Fernandez"}};

// Query for items with price greater than 9.99.
var query = from i in items
             where i.Price > 9.99
             orderby i.Price
             select i;

// Load the query results into new DataTable.
DataTable table = query.CopyToDataTable();
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()

EsempioExample

Nell'esempio seguente viene eseguita una query su una raccolta per ottenere gli articoli con prezzo maggiore di 9,99 $ e vengono proiettati i risultati.The following example queries a collection for items of price greater than 9.99 and projects the results. La sequenza di tipi anonimi restituiti viene caricata in una tabella esistente.The returned sequence of anonymous types is loaded into an existing table.

// Create a sequence. 
Item[] items = new Item[] 
{ new Book{Id = 1, Price = 13.50, Genre = "Comedy", Author = "Gustavo Achong"}, 
  new Book{Id = 2, Price = 8.50, Genre = "Drama", Author = "Jessie Zeng"},
  new Movie{Id = 1, Price = 22.99, Genre = "Comedy", Director = "Marissa Barnes"},
  new Movie{Id = 1, Price = 13.40, Genre = "Action", Director = "Emmanuel Fernandez"}};

// Create a table with a schema that matches that of the query results.            
DataTable table = new DataTable();
table.Columns.Add("Price", typeof(int));
table.Columns.Add("Genre", typeof(string));

var query = from i in items
             where i.Price > 9.99
             orderby i.Price
             select new { i.Price, i.Genre };

query.CopyToDataTable(table, LoadOption.PreserveChanges);
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)

EsempioExample

Nell'esempio seguente viene eseguita una query su una raccolta per ottenere gli articoli con prezzo maggiore di 9,99 $ e vengono proiettati i risultati.The following example queries a collection for items of price greater than $9.99 and projects the results. La sequenza di tipi anonimi restituiti viene caricata in una tabella esistente.The returned sequence of anonymous types is loaded into an existing table. Lo schema della tabella viene automaticamente espanso perché i tipi Book e Movies sono derivati dal tipo Item.The table schema is automatically expanded because the Book and Movies types are derived from the Item type.

// Create a sequence. 
Item[] items = new Item[] 
{ new Book{Id = 1, Price = 13.50, Genre = "Comedy", Author = "Gustavo Achong"}, 
  new Book{Id = 2, Price = 8.50, Genre = "Drama", Author = "Jessie Zeng"},
  new Movie{Id = 1, Price = 22.99, Genre = "Comedy", Director = "Marissa Barnes"},
  new Movie{Id = 1, Price = 13.40, Genre = "Action", Director = "Emmanuel Fernandez"}};

// Load into an existing DataTable, expand the schema and
// autogenerate a new Id.
DataTable table = new DataTable();
DataColumn dc = table.Columns.Add("NewId", typeof(int));
dc.AutoIncrement = true;
table.Columns.Add("ExtraColumn", typeof(string));

var query = from i in items
             where i.Price > 9.99
             orderby i.Price
             select new { i.Price, i.Genre };

query.CopyToDataTable(table, LoadOption.PreserveChanges);
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)

EsempioExample

Nell'esempio seguente viene eseguita una query su una raccolta per ottenere gli articoli con prezzo maggiore di 9,99 $ e viene restituita una sequenza di oggetti Double, che viene caricata in una nuova tabella.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.

// Create a sequence. 
Item[] items = new Item[] 
{ new Book{Id = 1, Price = 13.50, Genre = "Comedy", Author = "Gustavo Achong"}, 
  new Book{Id = 2, Price = 8.50, Genre = "Drama", Author = "Jessie Zeng"},
  new Movie{Id = 1, Price = 22.99, Genre = "Comedy", Director = "Marissa Barnes"},
  new Movie{Id = 1, Price = 13.40, Genre = "Action", Director = "Emmanuel Fernandez"}};

// load sequence of scalars.
IEnumerable<double> query = from i in items
             where i.Price > 9.99
             orderby i.Price
             select i.Price;

DataTable table = query.CopyToDataTable();
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()

Vedere ancheSee also