Entity Framework 中的導覽屬性是用來定位關聯末端實體的快捷屬性。 流覽屬性可讓使用者從某個實體巡覽到另一個實體，或透過關聯集從某個實體巡覽至相關實體。 本主題提供查詢表達式語法中的範例，說明如何透過 LINQ to Entities 查詢中的導覽屬性巡覽關聯性。
這些範例中使用的 AdventureWorks 銷售模型是從 AdventureWorks 範例資料庫中的 Contact、Address、Product、SalesOrderHeader 和 SalesOrderDetail 數據表所建置。
本主題中的範例會使用下列 using/Imports 語句：
using System;
using System.Data;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Objects;
using System.Globalization;
using System.Data.EntityClient;
using System.Data.SqlClient;
using System.Data.Common;
Option Explicit On
Option Strict On
Imports System.Data.Objects
Imports System.Globalization
範例 1
下列範例會使用 Select 方法來取得所有聯繫人標識符，以及姓氏為 “周” 的每個聯繫人應得的總和。
Contact.SalesOrderHeader 導覽屬性可用來取得每個聯繫人 SalesOrderHeader 物件的集合。
Sum 方法會使用 Contact.SalesOrderHeader 導覽屬性來加總每個聯繫人的所有訂單的應付款總額。
string lastName = "Zhou";
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
ObjectSet<Contact> contacts = context.Contacts;
var ordersQuery = from contact in contacts
where contact.LastName == lastName
select new
{
ContactID = contact.ContactID,
Total = contact.SalesOrderHeaders.Sum(o => o.TotalDue)
};
foreach (var contact in ordersQuery)
{
Console.WriteLine($"Contact ID: {contact.ContactID} Orders total: {contact.Total}");
}
}
Dim lastName = "Zhou"
Using context As New AdventureWorksEntities
Dim contacts As ObjectSet(Of Contact) = context.Contacts
Dim ordersQuery = From contact In contacts _
Where contact.LastName = lastName _
Select New With _
{.ContactID = contact.ContactID, _
.Total = contact.SalesOrderHeaders.Sum(Function(o) o.TotalDue)}
For Each order In ordersQuery
Console.WriteLine("Contact ID: {0} Orders total: {1}", order.ContactID, order.Total)
Next
End Using
範例 2
下列範例會取得姓氏為 「周」 之聯繫人的所有訂單。
Contact.SalesOrderHeader 導覽屬性可用來取得每個聯繫人 SalesOrderHeader 物件的集合。 聯繫人的名稱和訂單會以匿名類型傳回。
string lastName = "Zhou";
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
ObjectSet<Contact> contacts = context.Contacts;
var ordersQuery = from contact in contacts
where contact.LastName == lastName
select new { LastName = contact.LastName, Orders = contact.SalesOrderHeaders };
foreach (var order in ordersQuery)
{
Console.WriteLine($"Name: {order.LastName}");
foreach (SalesOrderHeader orderInfo in order.Orders)
{
Console.WriteLine("Order ID: {0}, Order date: {1}, Total Due: {2}",
orderInfo.SalesOrderID, orderInfo.OrderDate, orderInfo.TotalDue);
}
Console.WriteLine("");
}
}
Dim lastName = "Zhou"
Using context As New AdventureWorksEntities
Dim contacts As ObjectSet(Of Contact) = context.Contacts
Dim ordersQuery = From contact In contacts _
Where contact.LastName = lastName _
Select New With _
{.LastName = contact.LastName, _
.Orders = contact.SalesOrderHeaders}
For Each order In ordersQuery
Console.WriteLine("Name: {0}", order.LastName)
For Each orderInfo In order.Orders
Console.WriteLine("Order ID: {0}, Order date: {1}, Total Due: {2}", _
orderInfo.SalesOrderID, orderInfo.OrderDate, orderInfo.TotalDue)
Next
Console.WriteLine("")
Next
End Using
範例 3
下列範例會使用 SalesOrderHeader.Address 和 SalesOrderHeader.Contact 導覽屬性來取得與每個訂單相關聯的 Address 和 Contact 物件集合。 聯繫人的姓氏、街道地址、銷售訂單號碼，以及每筆訂單的到期總金額，都會以匿名類型的格式傳回至西雅圖市。
string city = "Seattle";
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;
var ordersQuery = from order in orders
where order.Address.City == city
select new
{
ContactLastName = order.Contact.LastName,
ContactFirstName = order.Contact.FirstName,
StreetAddress = order.Address.AddressLine1,
OrderNumber = order.SalesOrderNumber,
TotalDue = order.TotalDue
};
foreach (var orderInfo in ordersQuery)
{
Console.WriteLine("Name: {0}, {1}", orderInfo.ContactLastName, orderInfo.ContactFirstName);
Console.WriteLine($"Street address: {orderInfo.StreetAddress}");
Console.WriteLine($"Order number: {orderInfo.OrderNumber}");
Console.WriteLine($"Total Due: {orderInfo.TotalDue}");
Console.WriteLine("");
}
}
Dim city = "Seattle"
Using context As New AdventureWorksEntities
Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders
Dim ordersQuery = From order In orders _
Where order.Address.City = city _
Select New With { _
.ContactLastName = order.Contact.LastName, _
.ContactFirstName = order.Contact.FirstName, _
.StreetAddress = order.Address.AddressLine1, _
.OrderNumber = order.SalesOrderNumber, _
.TotalDue = order.TotalDue}
For Each orderInfo In ordersQuery
Console.WriteLine("Name: {0}, {1}", orderInfo.ContactLastName, orderInfo.ContactFirstName)
Console.WriteLine("Street address: {0}", orderInfo.StreetAddress)
Console.WriteLine("Order number: {0}", orderInfo.OrderNumber)
Console.WriteLine("Total Due: {0}", orderInfo.TotalDue)
Console.WriteLine("")
Next
End Using
範例 4
下列範例會使用 Where 方法來尋找在 2003 年 12 月 1 日之後所做的訂單，然後使用 order.SalesOrderDetail 導覽屬性來取得每個訂單的詳細數據。
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
IQueryable<SalesOrderHeader> query =
from order in context.SalesOrderHeaders
where order.OrderDate >= new DateTime(2003, 12, 1)
select order;
Console.WriteLine("Orders that were made after December 1, 2003:");
foreach (SalesOrderHeader order in query)
{
Console.WriteLine($"OrderID {order.SalesOrderID} Order date: {order.OrderDate:d} ");
foreach (SalesOrderDetail orderDetail in order.SalesOrderDetails)
{
Console.WriteLine($" Product ID: {orderDetail.ProductID} Unit Price {orderDetail.UnitPrice}");
}
}
}
Using context As New AdventureWorksEntities
Dim orders As ObjectSet(Of SalesOrderHeader) = context.SalesOrderHeaders
Dim query = _
From order In orders _
Where order.OrderDate >= New DateTime(2003, 12, 1) _
Select order
Console.WriteLine("Orders that were made after December 1, 2003:")
For Each order In query
Console.WriteLine("OrderID {0} Order date: {1:d} ", _
order.SalesOrderID, order.OrderDate)
For Each orderDetail In order.SalesOrderDetails
Console.WriteLine(" Product ID: {0} Unit Price {1}", _
orderDetail.ProductID, orderDetail.UnitPrice)
Next
Next
End Using