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以方法為基礎的查詢語法範例：聯結 (LINQ to DataSet)

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在以彼此沒有可瀏覽關聯性之資料來源 (例如關聯式資料庫資料表) 為目標的查詢中，聯結 (Join) 是一項重要的作業。 兩個資料來源的聯結是指某個資料來源中的物件與另一個資料來源中共用相同屬性之物件的關聯。 如需詳細資訊，請參閱標準查詢運算子概觀 (C#) 或標準查詢運算子概觀 (Visual Basic)。

此主題中的範例將示範如何使用 Join 方法並搭配方法查詢語法來查詢 DataSet。

將資料載入 DataSet 中指定了這些範例使用的 FillDataSet 方法。

此主題中的範例將使用 AdventureWorks 範例資料庫中的 Contact、Address、Product、SalesOrderHeader 和 SalesOrderDetail 資料表。

此主題中的範例使用下列 using/Imports 陳述式：

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

如需詳細資訊，請參閱操作說明：在 Visual Studio 中建立 LINQ to DataSet 專案。

聯結

範例

這則範例會在 Contact 和 SalesOrderHeader 資料表上方執行聯結。

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

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

var query =
    contacts.AsEnumerable().Join(orders.AsEnumerable(),
    order => order.Field<Int32>("ContactID"),
    contact => contact.Field<Int32>("ContactID"),
    (contact, order) => new
    {
        ContactID = contact.Field<Int32>("ContactID"),
        SalesOrderID = order.Field<Int32>("SalesOrderID"),
        FirstName = contact.Field<string>("FirstName"),
        Lastname = contact.Field<string>("Lastname"),
        TotalDue = order.Field<decimal>("TotalDue")
    });

foreach (var contact_order in query)
{
    Console.WriteLine("ContactID: {0} "
                    + "SalesOrderID: {1} "
                    + "FirstName: {2} "
                    + "Lastname: {3} "
                    + "TotalDue: {4}",
        contact_order.ContactID,
        contact_order.SalesOrderID,
        contact_order.FirstName,
        contact_order.Lastname,
        contact_order.TotalDue);
}

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

Dim query = _
    contacts.AsEnumerable().Join(orders.AsEnumerable(), _
    Function(order) order.Field(Of Int32)("ContactID"), _
    Function(contact) contact.Field(Of Int32)("ContactID"), _
    Function(contact, order) New With _
        { _
            .ContactID = contact.Field(Of Int32)("ContactID"), _
            .SalesOrderID = order.Field(Of Int32)("SalesOrderID"), _
            .FirstName = contact.Field(Of String)("FirstName"), _
            .Lastname = contact.Field(Of String)("Lastname"), _
            .TotalDue = order.Field(Of Decimal)("TotalDue") _
        })

For Each contact_order In query
    Console.WriteLine("ContactID: {0} " _
                    & "SalesOrderID: {1} " _
                    & "FirstName: {2} " _
                    & "Lastname: {3} " _
                    & "TotalDue: {4}", _
        contact_order.ContactID, _
        contact_order.SalesOrderID, _
        contact_order.FirstName, _
        contact_order.Lastname, _
        contact_order.TotalDue)
Next

範例

這則範例會在 Contact 和 SalesOrderHeader 資料表上方執行聯結，並依據連絡人識別碼分組結果。

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

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

var query = contacts.AsEnumerable().Join(orders.AsEnumerable(),
    order => order.Field<Int32>("ContactID"),
    contact => contact.Field<Int32>("ContactID"),
    (contact, order) => new
    {
        ContactID = contact.Field<Int32>("ContactID"),
        SalesOrderID = order.Field<Int32>("SalesOrderID"),
        FirstName = contact.Field<string>("FirstName"),
        Lastname = contact.Field<string>("Lastname"),
        TotalDue = order.Field<decimal>("TotalDue")
    })
        .GroupBy(record => record.ContactID);

foreach (var group in query)
{
    foreach (var contact_order in group)
    {
        Console.WriteLine("ContactID: {0} "
                        + "SalesOrderID: {1} "
                        + "FirstName: {2} "
                        + "Lastname: {3} "
                        + "TotalDue: {4}",
            contact_order.ContactID,
            contact_order.SalesOrderID,
            contact_order.FirstName,
            contact_order.Lastname,
            contact_order.TotalDue);
    }
}

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

Dim query = _
    contacts.AsEnumerable().Join(orders.AsEnumerable(), _
    Function(order) order.Field(Of Int32)("ContactID"), _
    Function(contact) contact.Field(Of Int32)("ContactID"), _
        Function(contact, order) New With _
        { _
            .ContactID = contact.Field(Of Int32)("ContactID"), _
            .SalesOrderID = order.Field(Of Int32)("SalesOrderID"), _
            .FirstName = contact.Field(Of String)("FirstName"), _
            .Lastname = contact.Field(Of String)("Lastname"), _
            .TotalDue = order.Field(Of Decimal)("TotalDue") _
        }) _
        .GroupBy(Function(record) record.ContactID)

For Each group In query
    For Each contact_order In group
        Console.WriteLine("ContactID: {0} " _
                        & "SalesOrderID: {1} " _
                        & "FirstName: {2} " _
                        & "Lastname: {3} " _
                        & "TotalDue: {4}", _
            contact_order.ContactID, _
            contact_order.SalesOrderID, _
            contact_order.FirstName, _
            contact_order.Lastname, _
            contact_order.TotalDue)
    Next
Next

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