Příklady syntaxe výrazů dotazů: Dělení (LINQ to DataSet)

  • Článek

Příklady v tomto tématu ukazují, jak pomocí Skip metod Take dotazovat DataSet pomocí syntaxe výrazu dotazu.

Metoda použitá FillDataSet v těchto příkladech je určena v načítání dat do datové sady.

Příklady v tomto tématu používají tabulky Contact, Address, Product, SalesOrderHeader a SalesOrderDetail v ukázkové databázi AdventureWorks.

Příklady v tomto tématu používají následující using/Imports příkazy:

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

Další informace naleznete v tématu Postupy: Vytvoření projektu LINQ to DataSet v sadě Visual Studio.

Přeskočit

Příklad

Tento příklad používá metodu Skip k získání všech adres kromě prvních dvou adres v Seattlu.

// 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);
}

' 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

Take

Příklad

Tento příklad používá metodu Take k získání prvních tří adres v Seattlu.

// 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);
}

' 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

Viz také