查詢運算式語法範例：聯結運算子 (LINQ to DataSet)

發行項
08/21/2008

更新： November 2007

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。

此主題中的範例將示範如何使用 GroupJoin 和 Join 方法並搭配查詢運算式語法來查詢 DataSet。

在這些範例中使用的 FillDataSet 方法指定於將資料載入 DataSet。

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。

此主題中的範例將使用下列 using/Imports 陳述式：

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;

如需詳細資訊，請參閱 HOW TO：在 Visual Studio 中建立 LINQ to DataSet 專案。

GroupJoin

範例

這則範例會針對 SalesOrderHeader 和 SalesOrderDetail 資料表執行 GroupJoin，以便尋找每位客戶的訂單數目。群組聯結是左外部聯結 (Left Outer Join) 的對等項目，它會傳回第一個 (左) 資料來源的每個項目，即使其他資料來源中沒有相互關聯的項目也一樣。

' 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 orders = ds.Tables("SalesOrderHeader").AsEnumerable()
Dim details = ds.Tables("SalesOrderDetail").AsEnumerable()

Dim query = _
        From order In orders _
        Group Join detail In details _
            On order.Field(Of Integer)("SalesOrderID") _
            Equals detail.Field(Of Integer)("SalesOrderID") Into ords = Group _
        Select New With _
            { _
                .CustomerID = order.Field(Of Integer)("SalesOrderID"), _
                .ords = ords.Count() _
            }

For Each order In query
    Console.WriteLine("CustomerID: {0}  Orders Count: {1}", _
        order.CustomerID, order.ords)
Next

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

var orders = ds.Tables["SalesOrderHeader"].AsEnumerable();
var details = ds.Tables["SalesOrderDetail"].AsEnumerable();

var query =
    from order in orders
    join detail in details
    on order.Field<int>("SalesOrderID")
    equals detail.Field<int>("SalesOrderID") into ords
    select new
    {
        CustomerID =
            order.Field<int>("SalesOrderID"),
        ords = ords.Count()
    };

foreach (var order in query)
{
    Console.WriteLine("CustomerID: {0}  Orders Count: {1}",
        order.CustomerID,
        order.ords);
}

範例

這則範例會針對 Contact 和 SalesOrderHeader 資料表執行 GroupJoin。群組聯結是左外部聯結的對等項目，它會傳回第一個 (左) 資料來源的每個項目，即使其他資料來源中沒有相互關聯的項目也一樣。

' 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 = _
    From contact In contacts.AsEnumerable(), order In orders.AsEnumerable() _
    Where (contact.Field(Of Integer)("ContactID") = _
        order.Field(Of Integer)("ContactID")) _
    Select New With _
        { _
            .ContactID = contact.Field(Of Integer)("ContactID"), _
            .SalesOrderID = order.Field(Of Integer)("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.Write("ContactID: " & contact_order.ContactID)
    Console.Write(" SalesOrderID: " & contact_order.SalesOrderID)
    Console.Write(" FirstName: " & contact_order.FirstName)
    Console.Write(" Lastname: " & contact_order.Lastname)
    Console.WriteLine(" TotalDue: " & contact_order.TotalDue)
Next

// 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 =
    from contact in contacts.AsEnumerable()
    join order in orders.AsEnumerable()
    on contact.Field<Int32>("ContactID") equals
    order.Field<Int32>("ContactID")
    select 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);
}

Join

範例

這則範例會針對 SalesOrderHeader 和 SalesOrderDetail 資料表執行聯結，以便取得八月份的線上訂單。

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


Dim query = _
    From order In orders.AsEnumerable() _
    Join detail In details.AsEnumerable() _
    On order.Field(Of Integer)("SalesOrderID") Equals _
            detail.Field(Of Integer)("SalesOrderID") _
    Where order.Field(Of Boolean)("OnlineOrderFlag") = True And _
            order.Field(Of DateTime)("OrderDate").Month = 8 _
    Select New With _
    { _
        .SalesOrderID = order.Field(Of Integer)("SalesOrderID"), _
        .SalesOrderDetailID = detail.Field(Of Integer)("SalesOrderDetailID"), _
        .OrderDate = order.Field(Of DateTime)("OrderDate"), _
        .ProductID = detail.Field(Of Integer)("ProductID") _
    }

For Each order In query
    Console.WriteLine(order.SalesOrderID & vbTab & _
        order.SalesOrderDetailID & vbTab & _
        order.OrderDate & vbTab & _
        order.ProductID)
Next

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

DataTable orders = ds.Tables["SalesOrderHeader"];
DataTable details = ds.Tables["SalesOrderDetail"];

var query =
    from order in orders.AsEnumerable()
    join detail in details.AsEnumerable()
    on order.Field<int>("SalesOrderID") equals
        detail.Field<int>("SalesOrderID")
    where order.Field<bool>("OnlineOrderFlag") == true
    && order.Field<DateTime>("OrderDate").Month == 8
    select new
    {
        SalesOrderID =
            order.Field<int>("SalesOrderID"),
        SalesOrderDetailID =
            detail.Field<int>("SalesOrderDetailID"),
        OrderDate =
            order.Field<DateTime>("OrderDate"),
        ProductID =
            detail.Field<int>("ProductID")
    };


foreach (var order in query)
{
    Console.WriteLine("{0}\t{1}\t{2:d}\t{3}",
        order.SalesOrderID,
        order.SalesOrderDetailID,
        order.OrderDate,
        order.ProductID);
}