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Method-Based 查詢語法範例：聯結（LINQ to DataSet）

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在查詢過程中，聯結是一個重要的作業，特別是針對那些沒有直接關聯的數據來源，如關係資料庫的數據表。 將兩個數據源聯結起來，指的是將一個數據源中的物件與另一個數據源中具有共同屬性的物件進行關聯。 如需詳細資訊，請參閱 標準查詢運算符概觀 （C#） 或 標準查詢運算子概觀 （Visual Basic）。

本主題中的範例示範如何使用 Join 方法，使用 方法查詢語法來查詢 DataSet。

這些範例中使用的 FillDataSet 方法在 將數據載入 DataSet中有指定。

本主題中的範例會使用 AdventureWorks 範例資料庫中的 Contact、Address、Product、SalesOrderHeader 和 SalesOrderDetail 數據表。

本主題中的範例會使用下列 using/Imports 語句：

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 如何：在 Visual Studio 中建立 LINQ to DataSet 專案。

加入

範例

這個範例會透過 Contact 和 SalesOrderHeader 數據表執行聯結。

// 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: {contact_order.ContactID} "
                    + "SalesOrderID: {contact_order.SalesOrderID} "
                    + "FirstName: {contact_order.FirstName} "
                    + "Lastname: {contact_order.Lastname} "
                    + "TotalDue: {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

此範例會透過 Contact 和 SalesOrderHeader 數據表執行聯結，並以聯繫人標識符分組結果。

// 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: {contact_order.ContactID} "
                        + "SalesOrderID: {contact_order.SalesOrderID} "
                        + "FirstName: {contact_order.FirstName} "
                        + "Lastname: {contact_order.Lastname} "
                        + "TotalDue: {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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