Crear un objeto DataTable a partir de una consulta (LINQ to DataSet)Creating a DataTable From a Query (LINQ to DataSet)

El enlace de datos es una utilización muy frecuente del objeto DataTable.Data binding is a common use of DataTable object. El método CopyToDataTable toma los resultados de una consulta y copia los datos en un objeto DataTable que puede utilizarse después para el enlace de datos.The CopyToDataTable method takes the results of a query and copies the data into a DataTable, which can then be used for data binding. Cuando las operaciones de datos se han realizado, el DataTable nuevo se vuelve a combinar en el DataTable de origen.When the data operations have been performed, the new DataTable is merged back into the source DataTable.

El método CopyToDataTable utiliza el siguiente proceso para crear un DataTable a partir de una consulta:The CopyToDataTable method uses the following process to create a DataTable from a query:

  1. El método CopyToDataTable clona un DataTable a partir de la tabla origen (un objeto DataTable que implementa la interfaz IQueryable<T>).The CopyToDataTable method clones a DataTable from the source table (a DataTable object that implements the IQueryable<T> interface). El IEnumerable origen se ha originado normalmente a partir de una expresión de LINQ to DataSet o una consulta de método.The IEnumerable source has generally originated from a LINQ to DataSet expression or method query.

  2. El esquema del DataTable clonado se compila a partir de las columnas del primer objeto DataRow enumerado en la tabla origen; el nombre de la tabla clonada es el nombre de la tabla origen con la palabra "query" anexada.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. En cada fila de la tabla origen, el contenido de la fila se copia en un objetoDataRow nuevo, el cual, a continuación, se inserta en la tabla clonada.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. Las propiedades RowState y RowError se mantienen en toda la operación de copia.The RowState and RowError properties are preserved across the copy operation. Si los objetos ArgumentException de origen pertenecen a tablas diferentes, se produce unaDataRow.An ArgumentException is thrown if the DataRow objects in the source are from different tables.

  4. Cuando todos los objetos DataTable de la tabla de entrada que se puede consultar se han copiado, se devuelve el DataRow clonado.The cloned DataTable is returned after all DataRow objects in the input queryable table have been copied. Si la secuencia origen no contiene objetos DataRow, el método devuelve un DataTable vacío.If the source sequence does not contain any DataRow objects, the method returns an empty DataTable.

Observe que, si se llama al método CopyToDataTable, la consulta se enlaza a la tabla origen para ejecutarse.Note that calling the CopyToDataTable method will cause the query bound to the source table to execute.

Cuando el método CopyToDataTable encuentra una referencia NULL o un tipo de valor que admite valores NULL en una fila de la tabla origen, reemplaza el valor 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. De este modo, los valores NULL se controlan correctamente en el DataTable devuelto.This way, null values are handled correctly in the returned DataTable.

Nota: El CopyToDataTable método acepta como entrada una consulta que puede devolver filas de varios DataTable objetos DataSet o.Note: The CopyToDataTable method accepts as input a query that can return rows from multiple DataTable or DataSet objects. El método CopyToDataTable copiará los datos pero no las propiedades desde los objetos DataTable o DataSet de origen en el elemento DataTable que se va a devolver.The CopyToDataTable method will copy the data but not the properties from the source DataTable or DataSet objects to the returned DataTable. Necesitará establecer explícitamente las propiedades de los elementos DataTable devueltos, como Locale y TableName.You will need to explicitly set the properties on the returned DataTable, such as Locale and TableName.

En el ejemplo siguiente se consultan en la tabla SalesOrderHeader los pedidos posteriores al 8 de agosto de 2001 y se utiliza el método CopyToDataTable para crear un DataTable a partir de esa consulta.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. A continuación, se enlaza DataTable a un BindingSource, que actúa como proxy para un objeto 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

Crear un método ><CopyToDataTable T personalizadoCreating a Custom CopyToDataTable<T> Method

Los métodos CopyToDataTable existentes solo funcionan en un origen IEnumerable<T> en el que el parámetro genérico T es de tipo DataRow.The existing CopyToDataTable methods only operate on an IEnumerable<T> source where the generic parameter T is of type DataRow. Aunque esto es útil, no permite la creación de tablas a partir de una secuencia de tipos escalares, a partir de consultas que devuelven tipos anónimos, o a partir de consultas que realizan combinaciones de tablas.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. Para obtener un ejemplo de cómo implementar dos métodos CopyToDataTable personalizados que cargan una tabla a partir de una secuencia de tipos escalares o anónimos, vea cómo: Implemente<CopyToDataTable T > donde el tipo genérico t no sea unaDataRow.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.

Los ejemplos de esta sección utilizan los tipos personalizados siguientes: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

EjemploExample

En este ejemplo se realiza una combinación en las tablas SalesOrderHeader y SalesOrderDetail para obtener pedidos en línea del mes de agosto y se crea una tabla a partir de la consulta.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()

EjemploExample

En el ejemplo siguiente se consulta una colección de elementos cuyo precio es superior a $ 9,99 y se crea una tabla a partir de los resultados de la consulta.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()

EjemploExample

En el ejemplo siguiente se consulta una colección de elementos cuyo precio es superior a $ 9,99 y se proyectan los resultados.The following example queries a collection for items of price greater than 9.99 and projects the results. La secuencia de tipos anónimos devuelta se carga en una tabla existente.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)

EjemploExample

En el ejemplo siguiente se consulta una colección de elementos cuyo precio es superior a $ 9,99 y se proyectan los resultados.The following example queries a collection for items of price greater than $9.99 and projects the results. La secuencia de tipos anónimos devuelta se carga en una tabla existente.The returned sequence of anonymous types is loaded into an existing table. El esquema de la tabla se amplía automáticamente porque los tipos Book y Movies se derivan del 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)

EjemploExample

En el ejemplo siguiente se consulta una colección de elementos cuyo precio es superior a $ 9,99 y se devuelve una secuencia de Double, que se carga en una tabla nueva.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()

Vea tambiénSee also