ASP.NET EF(LINQ/Lambda查询)
Posted DrHao
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EF(EntityFrameWork) ORM(对象关系映射框架/数据持久化框架)，根据实体对象操作数据表中数据的一种面向对象的操作框架，底层也是调用ADO.NET
ASP.NET MVC 项目会自动导入MVC程序集，因为默认.NET环境(GAC)中没有这个程序集
1 create database MyFirstEF 2 on primary 3 ( 4 name=\'MyFirstEF.mdf\', 5 --修改为自己电脑上SQL DB路径 6 filename=\'E:\\ProgramMSSQLServerDB\\MyFirstEF.mdf\', 7 size=5mb, 8 maxsize=100mb, 9 filegrowth=10% 10 ) 11 log on 12 ( 13 name=\'MyFirstEF_log.ldf\', 14 --修改为自己电脑上SQL DB路径 15 filename=\'E:\\ProgramMSSQLServerDB\\MyFirstEF_log.ldf\', 16 size=2mb, 17 maxsize=100mb, 18 filegrowth=5mb 19 ) 20 go 21 22 use MyFirstEF 23 go 24 25 create table CustomerInfo 26 ( 27 id int identity(1,1) primary key, 28 customerName nvarchar(100) not null, 29 customerDate datetime 30 ) 31 go 32 33 insert into CustomerInfo values(\'aaaaa\',getdate()) 34 go 35 36 select * from CustomerInfo 37 go 38 39 create table OrderInfo 40 ( 41 id int identity(1,1) primary key, 42 orderName nvarchar(100), 43 customerId int 44 ) 45 go 46 47 48 alter table OrderInfo 49 add constraint FK_OrderInfo_CustomerInfo 50 foreign key(customerId) references CustomerInfo(id) 51 on delete cascade 52 on update cascade 53 54 go 55 56 57 select * from CustomerInfo 58 select * from OrderInfo
1：LINQ[Language Integrated Query]/Lambda 基本查询
DbContext context = new MyFirstEFEntities(); // LINQ 基本查询 var rows = from c in context.Set<CustomerInfo>() select c; //返回的是SQL文 Console.WriteLine(rows); Console.WriteLine(rows.Count()); //Lambda 基本查询 var rows1 = context.Set<CustomerInfo>().Select(c => c); Console.WriteLine(rows1); Console.WriteLine(rows1.Count());
对应SQL为：
--基本查询 SELECT [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName], [Extent1].[customerDate] AS [customerDate] FROM [dbo].[CustomerInfo] AS [Extent1]
2：LINQ/Lambda 单条件查询
DbContext context = new MyFirstEFEntities(); //LINQ 单条件查询 var rows = from c in context.Set<CustomerInfo>() where c.id > 2 select c; Console.WriteLine(rows); Console.WriteLine(rows.Count()); //Lambda 单条件查询 var rows1 = context.Set<CustomerInfo>().Where(c => (c.id > 2)); Console.WriteLine(rows1); Console.WriteLine(rows1.Count());
对应SQL为：
--单条件查询 SELECT [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName], [Extent1].[customerDate] AS [customerDate] FROM [dbo].[CustomerInfo] AS [Extent1] WHERE [Extent1].[id] > 2
3：LINQ/Lambda 多条件查询
DbContext context = new MyFirstEFEntities(); //LINQ 多条件查询 var rows = from c in context.Set<CustomerInfo>() where c.id > 2 && c.customerName.Contains("today") select c; Console.WriteLine(rows); Console.WriteLine(rows.Count()); //Lambda 多条件查询 var rows1 = context.Set<CustomerInfo>().Where(c => (c.id > 2) && (c.customerName.Contains("today"))); Console.WriteLine(rows1); Console.WriteLine(rows1.Count());
对应SQL为：
--多条件查询 SELECT [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName], [Extent1].[customerDate] AS [customerDate] FROM [dbo].[CustomerInfo] AS [Extent1] WHERE ([Extent1].[id] > 2) AND ([Extent1].[customerName] LIKE N\'%today%\')
4：LINQ/Lambda 连接查询
DbContext context = new MyFirstEFEntities(); //LINQ 连接查询 var rows = from c in context.Set<CustomerInfo>() join o in context.Set<OrderInfo>() on c.id equals o.customerId select c; //连接查询相当于是Inner join Console.WriteLine(rows); Console.WriteLine(rows.Count()); //Lambda 连接查询 var rows1 = context.Set<CustomerInfo>().Join(context.Set<OrderInfo>(), c => c.id, o => o.customerId, (c, o) => c); Console.WriteLine(rows1); Console.WriteLine(rows1.Count());
对应SQL为：
--连接查询 SELECT [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName], [Extent1].[customerDate] AS [customerDate] FROM [dbo].[CustomerInfo] AS [Extent1] INNER JOIN [dbo].[OrderInfo] AS [Extent2] ON [Extent1].[id] = [Extent2].[customerId]
5：LINQ：多from查询：专用于有导航属性的查询(LINQ特有)
DbContext context = new MyFirstEFEntities(); //多from查询：专用于有导航属性的查询(LINQ特有) //select CustomerInfo var rows = from c in context.Set<CustomerInfo>() from o in c.OrderInfoes where c.id > 2 && o.orderName.Contains("car") select c; Console.WriteLine(rows); Console.WriteLine(rows.Count()); //select OrderInfo var rows1 = from c in context.Set<CustomerInfo>() from o in c.OrderInfoes where c.id > 2 && o.orderName.Contains("car") select o; Console.WriteLine(rows1); Console.WriteLine(rows1.Count());
对应SQL为：
--多from查询：专用于有导航属性的查询(LINQ特有) --select CustomerInfo SELECT [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName], [Extent1].[customerDate] AS [customerDate] FROM [dbo].[CustomerInfo] AS [Extent1] INNER JOIN [dbo].[OrderInfo] AS [Extent2] ON [Extent1].[id] = [Extent2].[customerId] WHERE ([Extent1].[id] > 2) AND ([Extent2].[orderName] LIKE N\'%car%\') --select OrderInfo SELECT [Extent1].[id] AS [id], [Extent1].[orderName] AS [orderName], [Extent1].[customerId] AS [customerId] FROM [dbo].[OrderInfo] AS [Extent1] WHERE ([Extent1].[customerId] IS NOT NULL) AND ([Extent1].[customerId] > 2) AND ([Extent1].[orderName] LIKE N\'%car%\')
6：LINQ/Lambda 查询部分列(指定列)
DbContext context = new MyFirstEFEntities(); //LINQ 查询部分列(指定列) var rows = from c in context.Set<CustomerInfo>() select new { Id = c.id, Name = c.customerName }; Console.WriteLine(rows); foreach (var row in rows) { Console.WriteLine(row.Id + ":" + row.Name); } //Lambda 查询部分列(指定列) var rows1 = context.Set<CustomerInfo>().Select(c => (new { Id = c.id, Name = c.customerName })); foreach (var row in rows1) { Console.WriteLine(row.Id + ":" + row.Name); }
对应SQL为：
--查询部分列(指定列) SELECT [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName] FROM [dbo].[CustomerInfo] AS [Extent1]
7：LINQ/Lambda 查询多个表格部分列(指定列)
DbContext context = new MyFirstEFEntities(); //LINQ 查询多个表格部分列 var rows = from c in context.Set<CustomerInfo>() join o in context.Set<OrderInfo>() on c.id equals o.customerId select new { CustomerName = c.customerName, OrderName = o.orderName }; Console.WriteLine(rows); Console.WriteLine(rows.Count()); var rows1 = context.Set<CustomerInfo>().Join(context.Set<OrderInfo>(), c => c.id, o => o.customerId, (c, o) => (new { CustomerName = c.customerName, OrderName = o.orderName })); Console.WriteLine(rows1); Console.WriteLine(rows1.Count());
对应SQL为：
--查询多个表格部分列(指定列) SELECT [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName], [Extent2].[orderName] AS [orderName] FROM [dbo].[CustomerInfo] AS [Extent1] INNER JOIN [dbo].[OrderInfo] AS [Extent2] ON [Extent1].[id] = [Extent2].[customerId]
8：Lambda：分页查询 lambda特有 OrderBy/Skip/Take
DbContext context = new MyFirstEFEntities(); int pageSize = 2; int pageIndex = 2; //需要构建出startIndex 和 EndedIndex var rows = context.Set<CustomerInfo>().OrderBy(c => c.id).Skip(pageSize * (pageIndex - 1)).Take(2); Console.WriteLine(rows); Console.WriteLine(rows.Count());
对应SQL为：
--分页查询 lambda特有 SELECT TOP (2) [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName], [Extent1].[customerDate] AS [customerDate] FROM ( SELECT [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName], [Extent1].[customerDate] AS [customerDate], row_number() OVER (ORDER BY [Extent1].[id] ASC) AS [row_number] FROM [dbo].[CustomerInfo] AS [Extent1] ) AS [Extent1] WHERE [Extent1].[row_number] > 2 ORDER BY [Extent1].[id] ASC
9：Lambda：封装分页查询
DbContext context1 = new MyFirstEFEntities(); int pageSize = 2; int pageIndex = 2; //var rows = context1.Set<CustomerInfo>().Where(c => c.id > 1).OrderBy(c => c.id).Skip(pageSize * (pageIndex - 1)).Take(pageSize); //Console.WriteLine(rows); //Console.WriteLine(rows.Count()); var rows1 = GetPageList<CustomerInfo, int>(context1, pageSize, pageIndex, c => c.id > 1, c => c.id); Console.WriteLine(rows1); Console.WriteLine(rows1.Count());
//泛型 委托 Lambda表达式 public static IQueryable<T> GetPageList<T, Tkey>(DbContext context, int pageSize, int pageIndex, Expression<Func<T, bool>> where, Expression<Func<T, Tkey>> orderBy) where T : class { var rows = context.Set<T>() //泛型约束，因为上下文的Set<T>()方法，对T有要求 .Where(where) //语法糖 将Lambda表达式封装为Expresson对象 .OrderBy(orderBy) .Skip(pageSize * (pageIndex - 1)) .Take(pageSize); return rows; }
对应SQL为：
SELECT TOP (2) [Filter1].[id] AS [id], [Filter1].[customerName] AS [customerName], [Filter1].[customerDate] AS [customerDate] FROM ( SELECT [Extent1].[id] AS [id], [Extent1].[customerName] AS [customerName], [Extent1].[customerDate] AS [customerDate], row_number() OVER (ORDER BY [Extent1].[id] ASC) AS [row_number] FROM [dbo].[CustomerInfo] AS [Extent1] WHERE [Extent1].[id] > 如何将带有内连接的 sql 查询转换为 linq lambda 表达式？