Ejemplos de sintaxis de consulta basada en métodos: creación de particiones (LINQ to DataSet)

Los ejemplos de este tema muestran cómo usar los métodos Skip<TSource>, SkipWhile, Take<TSource> y TakeWhile para consultar un DataSet usando la sintaxis de expresión de consultas.

El método FillDataSet utilizado en estos ejemplos se especifica en Cargar datos en DataSet.

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

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

Option Explicit On

Imports System
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

using System;
using System.Linq;
using System.Linq.Expressions;
using System.Collections.Generic;
using System.Data;
using System.Data.SqlClient;
using System.Data.Common;
using System.Globalization;

Para obtener más información, vea Cómo crear un proyecto LINQ to DataSet en Visual Studio.

Skip

Ejemplo

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

' 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

// 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 = {0} \tLastname = {1}",
        contact.Field<string>("FirstName"),
        contact.Field<string>("Lastname"));
}

Ejemplo

En este ejemplo se utiliza el método Skip<TSource> para obtener las dos primeras direcciones de Seattle.

' 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

// 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: {0} Order ID: {1} Total Due: {2:d}",
        order.City, order.OrderID, order.OrderDate);
}

SkipWhile

Ejemplo

En este ejemplo se utilizan los métodos OrderBy y SkipWhile para devolver productos de la tabla Product con un precio de venta superior a 300,00.

' 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

// 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"));
}

Take

Ejemplo

En este ejemplo se utiliza el método Take<TSource> para obtener únicamente los cinco primeros contactos de la tabla Contact.

' 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

// 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 = {0} \t FirstName = {1} \t Lastname = {2}",
        contact.Field<string>("Title"),
        contact.Field<string>("FirstName"),
        contact.Field<string>("Lastname"));
}

Ejemplo

En este ejemplo se utiliza el método Take<TSource> para obtener las tres primeras direcciones de Seattle.

' 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

// 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: {0} Order ID: {1} Total Due: {2:d}",
        order.City, order.OrderID, order.OrderDate);
}

TakeWhile

Ejemplo

En este ejemplo se utilizan los métodos OrderBy y TakeWhile para devolver de la tabla productos Product con un precio de venta inferior a 300,00.

' 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

// 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"));
}

Vea también

Conceptos

Cargar datos en DataSet

Información general sobre operadores de consulta estándar

Otros recursos

Ejemplos de LINQ to DataSet