C#教程之轻量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(10);

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(10);

            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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