轻量ORM-SqlRepoEx （六） JOIN

示例使用的是最新 SqlRepoEx 2.0.2

可在：https://github.com/AzThinker/SqlRepoEx2.0Demo

或：https://gitee.com/azthinker/SqlRepoEx2.0Demo

演示模块：GettingStartedNorthwind

1、新建一个控制台程序；

2、通过Nuget包管理，下载SqlRepoEx.MsSql.Static

3、根据Northwind数据库的 Orders、Customers、Employees三张表结构生成三个简单的同名类；

4、 创建初始方法，初始一个工厂类。

 /// <summary>
         /// init
         /// 创建初始方法，初始一个工厂类。
         /// </summary>
         static void Init()
         {
             // Set Connection String
             string ConnectionString = "Data Source=(Local);Initial Catalog=Northwind;User ID=test;Password=test";
             var connectionProvider = new ConnectionStringConnectionProvider(ConnectionString);
             MsSqlRepoFactory.UseConnectionProvider(connectionProvider);

             // this Demo is POJO ,So Using SimpleWritablePropertyMatcher()。
             // 本例中，使用的是简单类，所以用SimpleWritablePropertyMatcher()来操作属性。
             MsSqlRepoFactory.UseWritablePropertyMatcher(new SimpleWritablePropertyMatcher());
         }

5、为了演示JOIN 在 Orders类增加几个相关字段

（1）、关联Customers

　　public string CompanyName { get; set; }

（2）、  关联Employees

　　public string LastName { get; set; }

　　public string FirstName { get; set; }

6、实例一个Orders仓储

　　 var repoCustomers = MsSqlRepoFactory.Create<Orders>();

7、使用 SqlRepoEx 建立一个联接查询

 var cust = repoCustomers.Query().Select(c => c.OrderID, c => c.CompanyName, c => c.FirstName, c => c.LastName, c => c.OrderDate)
                                   .InnerJoin<Customers>()
                                   .On<Customers>((r, l) => r.CustomerID == l.CustomerID, l => l.CompanyName)
                                   .InnerJoin<Employees>()
                                   .On<Employees>((k, q) => k.EmployeeID == q.EmployeeID, q => q.FirstName, q => q.LastName)
                                   .Top();

8、此查询的实际 SQL 语句

Console.WriteLine(cust.Sql());

...

 SELECT TOP (10) [dbo].[Orders].[OrderID]
     , [dbo].[Customers].[CompanyName]
     , [dbo].[Employees].[FirstName]
     , [dbo].[Employees].[LastName]
     , [dbo].[Orders].[OrderDate]
 FROM [dbo].[Orders]
     INNER JOIN [dbo].[Customers]
     ON [dbo].[Orders].[CustomerID] = [dbo].[Customers].[CustomerID]
     INNER JOIN [dbo].[Employees]
     ON [dbo].[Orders].[EmployeeID] = [dbo].[Employees].[EmployeeID];

9、查询结果

 /// <summary>
         /// Join 演示
         /// </summary>
         public static void DoJoin()
         {
             var repoCustomers = MsSqlRepoFactory.Create<Orders>();

             var cust = repoCustomers.Query().Select(c => c.OrderID, c => c.CompanyName, c => c.FirstName, c => c.LastName, c => c.OrderDate)
                                   .InnerJoin<Customers>()
                                   .On<Customers>((r, l) => r.CustomerID == l.CustomerID, l => l.CompanyName)
                                   .InnerJoin<Employees>()
                                   .On<Employees>((k, q) => k.EmployeeID == q.EmployeeID, q => q.FirstName, q => q.LastName)
                                   .Top();

             Console.WriteLine(cust.Sql());

             foreach(var item in cust.Go())
             {
                 Console.WriteLine($"{item.OrderID}\t{item.CompanyName}\t{item.FirstName}\t{item.LastName}\t{item.OrderDate};");
             }

         }

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