Vytvoření objektu DataTable z dotazu (LINQ to DataSet)Creating a DataTable From a Query (LINQ to DataSet)

Datová vazba je běžné použití DataTable objektu.Data binding is a common use of DataTable object. CopyToDataTableMetoda přijímá výsledky dotazu a kopíruje data do DataTable , které lze následně použít pro datovou vazbu.The CopyToDataTable method takes the results of a query and copies the data into a DataTable, which can then be used for data binding. Po provedení operací s daty DataTable se nový sloučí zpátky do zdroje DataTable .When the data operations have been performed, the new DataTable is merged back into the source DataTable.

CopyToDataTableMetoda používá následující proces k vytvoření DataTable z dotazu:The CopyToDataTable method uses the following process to create a DataTable from a query:

  1. CopyToDataTableMetoda naklonuje DataTable ze zdrojové tabulky ( DataTable objekt, který implementuje IQueryable<T> rozhraní).The CopyToDataTable method clones a DataTable from the source table (a DataTable object that implements the IQueryable<T> interface). IEnumerableZdroj obecně pochází z výrazu LINQ to DataSet nebo dotazu metody.The IEnumerable source has generally originated from a LINQ to DataSet expression or method query.

  2. Schéma klonování DataTable je postavené ze sloupců prvního výčtového DataRow objektu ve zdrojové tabulce a názvem klonované tabulky je název zdrojové tabulky, ke které se připojí Word "dotaz".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. Pro každý řádek ve zdrojové tabulce se obsah řádku zkopíruje do nového DataRow objektu, který je pak vložen do klonované tabulky.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. RowStateVlastnosti a RowError jsou zachovány v rámci operace kopírování.The RowState and RowError properties are preserved across the copy operation. ArgumentExceptionPokud DataRow jsou objekty ve zdroji z různých tabulek, je vyvolána výjimka.An ArgumentException is thrown if the DataRow objects in the source are from different tables.

  4. Klonování DataTable se vrátí po DataRow zkopírování všech objektů ve vstupní tabulce Queryable.The cloned DataTable is returned after all DataRow objects in the input queryable table have been copied. Pokud zdrojová sekvence neobsahuje žádné DataRow objekty, metoda vrátí prázdnou hodnotu DataTable .If the source sequence does not contain any DataRow objects, the method returns an empty DataTable.

Volání CopyToDataTable metody způsobí provedení dotazu vázaného na zdrojovou tabulku.Calling the CopyToDataTable method causes the query bound to the source table to execute.

Když CopyToDataTable metoda nalezne buď odkaz na hodnotu null nebo typ hodnoty s možnou hodnotou null v řádku ve zdrojové tabulce, nahradí hodnotu hodnotou 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. Tímto způsobem se hodnoty null zpracovávají správně ve vrácených hodnotách DataTable .This way, null values are handled correctly in the returned DataTable.

Poznámka: CopyToDataTable Metoda přijímá jako vstup dotaz, který může vracet řádky z více DataTable objektů nebo DataSet .Note: The CopyToDataTable method accepts as input a query that can return rows from multiple DataTable or DataSet objects. CopyToDataTableMetoda zkopíruje data, ale nikoli vlastnosti ze zdroje DataTable nebo DataSet objektů do vráceného objektu DataTable .The CopyToDataTable method will copy the data but not the properties from the source DataTable or DataSet objects to the returned DataTable. Budete muset explicitně nastavit vlastnosti vrácených DataTable , například Locale a TableName .You will need to explicitly set the properties on the returned DataTable, such as Locale and TableName.

Následující příklad vyhledá tabulku SalesOrderHeader pro objednávky po 8. srpna 2001 a použije CopyToDataTable metodu k vytvoření DataTable z tohoto dotazu.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. DataTableJe pak svázán s BindingSource , který funguje jako proxy pro 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

Vytvoření vlastní metody CopyToDataTable <T>Creating a Custom CopyToDataTable<T> Method

Stávající CopyToDataTable metody fungují pouze ve IEnumerable<T> zdroji, kde je obecný parametr T typu DataRow .The existing CopyToDataTable methods only operate on an IEnumerable<T> source where the generic parameter T is of type DataRow. I když je to užitečné, neumožňuje vytvářet tabulky ze sekvence skalárních typů, od dotazů, které vracejí anonymní typy, nebo z dotazů, které provádějí spojení tabulek.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. Příklad toho, jak implementovat dvě vlastní CopyToDataTable metody, které načítají tabulku ze sekvence skalárních nebo anonymních typů, naleznete v tématu How to: Implement CopyToDataTable, <T> kde obecný typ T není 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.

Příklady v této části používají následující vlastní typy: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

PříkladExample

Tento příklad provede spojení SalesOrderHeader tabulek a a SalesOrderDetail získá online objednávky z měsíce srpna a vytvoří tabulku z dotazu.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()

PříkladExample

Následující příklad dotazuje kolekci pro položky Price větší než $9,99 a vytvoří tabulku z výsledků dotazu.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()

PříkladExample

Následující příklad dotazuje kolekci pro položky Price větší než 9,99 a výsledky projektů.The following example queries a collection for items of price greater than 9.99 and projects the results. Vrácená sekvence anonymních typů je načtena do existující tabulky.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)

PříkladExample

Následující příklad dotazuje kolekci pro položky Price větší než $9,99 a výsledky projektů.The following example queries a collection for items of price greater than $9.99 and projects the results. Vrácená sekvence anonymních typů je načtena do existující tabulky.The returned sequence of anonymous types is loaded into an existing table. Schéma tabulky je automaticky rozbaleno, protože Book Movies typy a jsou odvozeny z Item typu.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)

PříkladExample

Následující příklad vyhledá kolekci pro položky Price větší než $9,99 a vrátí sekvenci Double , která je načtena do nové tabulky.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()

Viz takéSee also