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Ejemplos de sintaxis de consulta de Method-Based: creación de particiones (LINQ)

Los ejemplos de este tema muestran cómo utilizar los métodos Skip, SkipWhile, Take y TakeWhile para consultar un DataSet usando la sintaxis de expresión de consulta.

El FillDataSet método usado en estos ejemplos se especifica en Carga de Datos en un DataSet.

Los ejemplos de este tema usan las tablas Contact, Address, Product, SalesOrderHeader y SalesOrderDetail de la base de datos de ejemplo AdventureWorks.

Los ejemplos de este tema utilizan las siguientes instrucciones using/Imports:

using System;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Globalization;
using System.Linq;
using System.Windows.Forms;

Option Explicit On

Imports System.Linq
Imports System.Linq.Expressions
Imports System.Collections.Generic
Imports System.Data
Imports System.Data.SqlClient
Imports System.Data.Common
Imports System.Globalization

Para obtener más información, vea How to: Create a LINQ to DataSet Project In Visual Studio.

Omitir

Ejemplo

En este ejemplo se utiliza el método Skip para obtener todos los contactos menos los cinco primeros de la tabla Contact.

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable contacts = ds.Tables["Contact"];

IEnumerable<DataRow> allButFirst5Contacts = contacts.AsEnumerable().Skip(5);

Console.WriteLine("All but first 5 contacts:");
foreach (DataRow contact in allButFirst5Contacts)
{
    Console.WriteLine($"FirstName = {contact.Field<string>("FirstName")} \tLastname = {contact.Field<string>("Lastname")}");
}

' 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 contacts As DataTable = ds.Tables("Contact")

Dim allButFirst5Contacts = contacts.AsEnumerable().Skip(5)

Console.WriteLine("All but first 5 contacts:")

For Each contact In allButFirst5Contacts
    Console.Write("FirstName = {0} ", contact.Field(Of String)("FirstName"))
    Console.WriteLine(vbTab & " LastName = " & contact.Field(Of String)("LastName"))
Next

Ejemplo

En este ejemplo se usa el método Skip para obtener todas las direcciones excepto las dos primeras en Seattle.

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

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

var query = (
    from address in addresses.AsEnumerable()
    from order in orders.AsEnumerable()
    where address.Field<int>("AddressID") == order.Field<int>("BillToAddressID")
         && address.Field<string>("City") == "Seattle"
    select new
    {
        City = address.Field<string>("City"),
        OrderID = order.Field<int>("SalesOrderID"),
        OrderDate = order.Field<DateTime>("OrderDate")
    }).Skip(2);

Console.WriteLine("All but first 2 orders in Seattle:");
foreach (var order in query)
{
    Console.WriteLine($"City: {order.City} Order ID: {order.OrderID} Total Due: {order.OrderDate:d}");
}

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

Dim query = ( _
    From address In addresses.AsEnumerable() _
    From order In orders.AsEnumerable() _
    Where (address.Field(Of Integer)("AddressID") = _
           order.Field(Of Integer)("BillToAddressID")) _
         And address.Field(Of String)("City") = "Seattle" _
    Select New With _
       { _
           .City = address.Field(Of String)("City"), _
           .OrderID = order.Field(Of Integer)("SalesOrderID"), _
           .OrderDate = order.Field(Of DateTime)("OrderDate") _
       }).Skip(2)

Console.WriteLine("All but first 2 orders in Seattle:")
For Each addOrder In query
    Console.Write("City: " & addOrder.City)
    Console.Write(" Order ID: " & addOrder.OrderID)
    Console.WriteLine(" Order date: " & addOrder.OrderDate)
Next

SkipWhile

Ejemplo

En este ejemplo se usan los métodos OrderBy y SkipWhile para devolver productos de la tabla Product con un precio de lista mayor que 300,00.

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable products = ds.Tables["Product"];

IEnumerable<DataRow> skipWhilePriceLessThan300 =
    products.AsEnumerable()
        .OrderBy(listprice => listprice.Field<decimal>("ListPrice"))
        .SkipWhile(product => product.Field<decimal>("ListPrice") < 300.00M);

Console.WriteLine("Skip while ListPrice is less than 300.00:");
foreach (DataRow product in skipWhilePriceLessThan300)
{
    Console.WriteLine(product.Field<decimal>("ListPrice"));
}

' 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 products As DataTable = ds.Tables("Product")
Dim skipWhilePriceLessThan300 As IEnumerable(Of DataRow) = _
    products.AsEnumerable() _
        .OrderBy(Function(listprice) listprice.Field(Of Decimal)("ListPrice")) _
        .SkipWhile(Function(product) product.Field(Of Decimal)("ListPrice") < 300D)

Console.WriteLine("First ListPrice less than 300.00:")
For Each product As DataRow In skipWhilePriceLessThan300
    Console.WriteLine(product.Field(Of Decimal)("ListPrice"))
Next

Tomar

Ejemplo

En este ejemplo se usa el método Take para obtener solo los primeros cinco contactos de la tabla Contact.

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable contacts = ds.Tables["Contact"];

IEnumerable<DataRow> first5Contacts = contacts.AsEnumerable().Take(5);

Console.WriteLine("First 5 contacts:");
foreach (DataRow contact in first5Contacts)
{
    Console.WriteLine($"Title = {contact.Field<string>("Title")} \t FirstName = {contact.Field<string>("FirstName")} \t Lastname = {contact.Field<string>("Lastname")}");
}

' 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 contacts As DataTable = ds.Tables("Contact")

Dim first5Contacts = contacts.AsEnumerable().Take(5)

Console.WriteLine("First 5 contacts:")
For Each contact In first5Contacts
    Console.Write("Title = " & contact.Field(Of String)("Title"))
    Console.Write(vbTab & "FirstName = " & contact.Field(Of String)("FirstName"))
    Console.WriteLine(vbTab & "LastName = " & contact.Field(Of String)("LastName"))
Next

Ejemplo

En este ejemplo se usa el Take método para obtener las tres primeras direcciones de Seattle.

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

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

var query = (
    from address in addresses.AsEnumerable()
    from order in orders.AsEnumerable()
    where address.Field<int>("AddressID") == order.Field<int>("BillToAddressID")
         && address.Field<string>("City") == "Seattle"
    select new
    {
        City = address.Field<string>("City"),
        OrderID = order.Field<int>("SalesOrderID"),
        OrderDate = order.Field<DateTime>("OrderDate")
    }).Take(3);

Console.WriteLine("First 3 orders in Seattle:");
foreach (var order in query)
{
    Console.WriteLine($"City: {order.City} Order ID: {order.OrderID} Total Due: {order.OrderDate:d}");
}

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

Dim query = ( _
    From address In addresses.AsEnumerable() _
    From order In orders.AsEnumerable() _
    Where (address.Field(Of Integer)("AddressID") = _
        order.Field(Of Integer)("BillToAddressID")) _
         And address.Field(Of String)("City") = "Seattle" _
    Select New With _
    { _
        .City = address.Field(Of String)("City"), _
        .OrderID = order.Field(Of Integer)("SalesOrderID"), _
        .OrderDate = order.Field(Of DateTime)("OrderDate") _
    }).Take(3)

Console.WriteLine("First 3 orders in Seattle:")
For Each order In query
    Console.Write("City: " & order.City)
    Console.Write(" Order ID: " & order.OrderID)
    Console.WriteLine(" Order date: " & order.OrderDate)
Next

TakeWhile

Ejemplo

En este ejemplo se usa OrderBy y TakeWhile para devolver productos de la Product tabla con un precio de lista inferior a 300.00.

// Fill the DataSet.
DataSet ds = new DataSet();
ds.Locale = CultureInfo.InvariantCulture;
FillDataSet(ds);

DataTable products = ds.Tables["Product"];

IEnumerable<DataRow> takeWhileListPriceLessThan300 =
    products.AsEnumerable()
        .OrderBy(listprice => listprice.Field<decimal>("ListPrice"))
        .TakeWhile(product => product.Field<decimal>("ListPrice") < 300.00M);

Console.WriteLine("First ListPrice less than 300:");
foreach (DataRow product in takeWhileListPriceLessThan300)
{
    Console.WriteLine(product.Field<decimal>("ListPrice"));
}

' 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 products As DataTable = ds.Tables("Product")

Dim takeWhileListPriceLessThan300 As IEnumerable(Of DataRow) = _
    products.AsEnumerable() _
        .OrderBy(Function(listprice) listprice.Field(Of Decimal)("ListPrice")) _
        .TakeWhile(Function(product) product.Field(Of Decimal)("ListPrice") < 300D)

Console.WriteLine("First ListPrice less than 300.00:")
For Each product As DataRow In takeWhileListPriceLessThan300
    Console.WriteLine(product.Field(Of Decimal)("ListPrice"))
Next

Consulte también