如何使用 Join 和 GroupJoin 方法通过基于方法的查询语法来查询-联接运算符

资料来源：网络整理时间：2023/2/14 0:50:24 共计：3609 浏览

本主题中的示例演示如何使用 Join 和 GroupJoin 方法通过基于方法的查询语法来查询 AdventureWorks 销售模型。这些示例中使用的 AdventureWorks 销售模型从 AdventureWorks 示例数据库中的 Contact、Address、Product、SalesOrderHeader 和 SalesOrderDetail 等表生成。

本主题中的示例使用以下 using / Imports 语句：

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;

GroupJoin

示例

以下示例针对 SalesOrderHeader 表和 SalesOrderDetail 表执行 GroupJoin 以查找每个客户的订单数。组联接等效于左外部联接，它返回第一个（左侧）数据源的每个元素（即使其他数据源中没有关联元素）。

using (AdventureWorksEntities context = new AdventureWorksEntities())

{

ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

ObjectSet<SalesOrderDetail> details = context.SalesOrderDetails;

var query = orders.GroupJoin(details,

order => order.SalesOrderID,

detail => detail.SalesOrderID,

(order, orderGroup) => new

{

CustomerID = order.SalesOrderID,

OrderCount = orderGroup.Count()

});

foreach (var order in query)

{

Console.WriteLine("CustomerID: {0} Orders Count: {1}",

order.CustomerID,

order.OrderCount);

}

示例

下面的示例对 Contact 和 SalesOrderHeader 表执行 GroupJoin 以查找每个联系人的订单数。将显示每个联系人的订单数和 ID。

using (AdventureWorksEntities context = new AdventureWorksEntities())

{

ObjectSet<Contact> contacts = context.Contacts;

ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

var query = contacts.GroupJoin(orders,

contact => contact.ContactID,

order => order.Contact.ContactID,

(contact, contactGroup) => new

{

ContactID = contact.ContactID,

OrderCount = contactGroup.Count(),

Orders = contactGroup

});

foreach (var group in query)

{

Console.WriteLine("ContactID: {0}", group.ContactID);

Console.WriteLine("Order count: {0}", group.OrderCount);

foreach (var orderInfo in group.Orders)

{

Console.WriteLine(" Sale ID: {0}", orderInfo.SalesOrderID);

}

Console.WriteLine("");

}

联接

示例

以下示例针对 Contact 表和 SalesOrderHeader 表执行联接。

using (AdventureWorksEntities context = new AdventureWorksEntities())

{

ObjectSet<Contact> contacts = context.Contacts;

ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

var query =

contacts.Join(

orders,

order => order.ContactID,

contact => contact.Contact.ContactID,

(contact, order) => new

{

ContactID = contact.ContactID,

SalesOrderID = order.SalesOrderID,

FirstName = contact.FirstName,

Lastname = contact.LastName,

TotalDue = order.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);

}

示例

以下示例针对 Contact 表和 SalesOrderHeader 表执行联接，同时按联系人 ID 对结果分组。

using (AdventureWorksEntities context = new AdventureWorksEntities())

{

ObjectSet<Contact> contacts = context.Contacts;

ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

var query = contacts.Join(

orders,

order => order.ContactID,

contact => contact.Contact.ContactID,

(contact, order) => new

{

ContactID = contact.ContactID,

SalesOrderID = order.SalesOrderID,

FirstName = contact.FirstName,

Lastname = contact.LastName,

TotalDue = order.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);

}

请参阅

LINQ to Entities 中的查询

版权说明：
本网站凡注明“广州京杭原创”的皆为本站原创文章，如需转载请注明出处！
本网转载皆注明出处，遵循行业规范，如发现作品内容版权或其它问题的，请与我们联系处理！
欢迎扫描右侧微信二维码与我们联系。

·上一条：如何使用 First 方法通过使用基于方法的查询语法来查询-元素运算符 | ·下一条：如何使用 ToArray ToDictionary 和 ToList 方法-转换