ASP.NET EF(LINQ/Lambda查询)

时间：2021-02-19 13:40:52

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

 create database MyFirstEF

 on primary

 (

     name='MyFirstEF.mdf',

     --修改为自己电脑上SQL DB路径

     filename='E:\ProgramMSSQLServerDB\MyFirstEF.mdf',

     size=5mb,

     maxsize=100mb,

     filegrowth=10%

 )

 log on

 (

     name='MyFirstEF_log.ldf',

     --修改为自己电脑上SQL DB路径

     filename='E:\ProgramMSSQLServerDB\MyFirstEF_log.ldf',

     size=2mb,

     maxsize=100mb,

     filegrowth=5mb

 )

 go

 use MyFirstEF

 go

 create table CustomerInfo

 (

     id int identity(1,1) primary key,

     customerName nvarchar(100) not null,

     customerDate datetime

 )

 go

 insert into CustomerInfo values('aaaaa',getdate())

 go

 select * from CustomerInfo

 go

 create table OrderInfo

 (

   id int identity(1,1) primary key,

   orderName nvarchar(100),

   customerId int

 )

 go

 alter table OrderInfo

 add constraint FK_OrderInfo_CustomerInfo

 foreign key(customerId) references CustomerInfo(id)

 on delete cascade

 on update cascade

 go

 select * from CustomerInfo

 select * from OrderInfo

create SQL

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 >

           select c;

Console.WriteLine(rows);

Console.WriteLine(rows.Count());

//Lambda 单条件查询

var rows1 = context.Set<CustomerInfo>().Where(c => (c.id > ));

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 >  && 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 > ) && (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 >  && 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 >  && 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 = ;

int pageIndex = ;

//需要构建出startIndex 和 EndedIndex

var rows = context.Set<CustomerInfo>().OrderBy(c => c.id).Skip(pageSize * (pageIndex - )).Take();

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 = ;

int pageIndex = ;

//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 > , 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 - ))

        .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] > 1

)  AS [Filter1]

WHERE [Filter1].[row_number] > 2

ORDER BY [Filter1].[id] ASC

整体EF 查询Demo源代码：

using System;

using System.Collections.Generic;

using System.Data.Entity;

using System.Data.Entity.Infrastructure;

using System.Linq;

using System.Linq.Expressions;

using System.Text;

using System.Threading.Tasks;

namespace _20160403_MyFirstEFDemo

{

    class Program

    {

        static void Main(string[] args)

        {

            #region 方法

            ////EF context 对象

            //MyFirstEFEntities context = new MyFirstEFEntities();

            ////add

            //CustomerInfo customer = new CustomerInfo();

            //customer.customerName = "Test1";

            //customer.customerDate = DateTime.Now;

            //context.CustomerInfoes.Add(customer);

            //context.SaveChanges();

            ////update

            ////1：先查询要修改的原数据

            //CustomerInfo customer = context.CustomerInfoes.Find(1);

            ////2：设置修改后的值

            //customer.customerDate = DateTime.Now;

            ////3：更新到数据库

            //context.SaveChanges();

            ////Read

            //CustomerInfo customer = context.CustomerInfoes.Find(1);

            //if (customer != null)

            //{

            //    string strCustomerInfo = string.Format("name:{0},date:{1}", customer.customerName, customer.customerDate);

            //    Console.WriteLine(strCustomerInfo);

            //}

            ////delete

            //CustomerInfo customer = new CustomerInfo();

            //customer.id = 1;

            //context.CustomerInfoes.Attach(customer);

            //context.CustomerInfoes.Remove(customer);

            //context.SaveChanges();

            #endregion

            #region 状态

            //EF context 对象

            //DbContext contextState = new MyFirstEFEntities();

            ////add 1

            //CustomerInfo customerState = new CustomerInfo();

            //customerState.customerName = "testState1";

            //customerState.customerDate = DateTime.Now;

            //contextState.Set<CustomerInfo>().Add(customerState);

            //contextState.SaveChanges();

            ////add 2

            //CustomerInfo customerState = new CustomerInfo() {

            //     customerName="stateTest111",

            //     customerDate=DateTime.Now

            //};

            //contextState.Entry<CustomerInfo>(customerState).State = System.Data.EntityState.Added;

            //contextState.SaveChanges();

            ////update 1

            //CustomerInfo customerState = new CustomerInfo();

            //customerState.id = 1;

            //customerState.customerDate = DateTime.Now;

            //customerState.customerName = "bbb";

            ////1: 标记当前对象，必须把必填字段都填写，否则会报错：System.Data.Entity.Validation.DbEntityValidationException

            ////1: 若此时未更新 非必填字段，则数据库会把非必填字段更新为null

            //contextState.Entry<CustomerInfo>(customerState).State = System.Data.EntityState.Modified;

            //contextState.SaveChanges();

            ////update 2

            //CustomerInfo customerState = new CustomerInfo();

            //customerState.id = 1;

            //customerState.customerName = "dfdfdfdf";

            ////2: 针对某个属性，进行状态跟踪设置

            ////** 2.1: 如果使用 Entry 附加 实体对象到数据容器中，则需要手动 设置 实体包装类的对象 的 状态为 Unchanged**

            ////** 2.1: entry.State = System.Data.EntityState.Unchanged;

            //DbEntityEntry<CustomerInfo> entry = contextState.Entry<CustomerInfo>(customerState);

            //entry.State = System.Data.EntityState.Unchanged;

            //entry.Property("customerName").IsModified = true;

            //contextState.SaveChanges();

            ////update 3

            //CustomerInfo customerState = new CustomerInfo();

            //customerState.id = 1;

            //customerState.customerName = "aaaaa";

            ////** 2.2: 如果使用 Attach 就不需要这句

            ////** 2.2: entry.State = System.Data.EntityState.Unchanged;

            //contextState.Set<CustomerInfo>().Attach(customerState);///直接针对属性进行状态设置，但是当前对象并没有被上下文跟踪

            //contextState.Entry<CustomerInfo>(customerState).Property("customerName").IsModified = true;

            //contextState.SaveChanges();

            ////delete

            //CustomerInfo customerState = new CustomerInfo()

            //{

            //    id = 2

            //};

            //contextState.Entry<CustomerInfo>(customerState).State = System.Data.EntityState.Deleted;

            //contextState.SaveChanges();

            #endregion

            #region 多表增加操作

            //DbContext dbContext = new MyFirstEFEntities();

            //CustomerInfo customerInfo = new CustomerInfo()

            //{

            //    customerName = "duobiaocaozuo",

            //    customerDate = DateTime.Now

            //};

            //dbContext.Set<CustomerInfo>().Add(customerInfo);

            //OrderInfo orderInfo1 = new OrderInfo()

            //{

            //    orderName = "bike1",

            //    customerId = customerInfo.id

            //};

            //dbContext.Set<OrderInfo>().Add(orderInfo1);

            //OrderInfo orderInfo2 = new OrderInfo()

            //{

            //    orderName = "bike2",

            //    customerId = customerInfo.id

            //};

            //dbContext.Set<OrderInfo>().Add(orderInfo2);

            //dbContext.SaveChanges();

            #endregion

            #region 导航属性

            //DbContext dbContext = new MyFirstEFEntities();

            //CustomerInfo customerInfo = new CustomerInfo()

            //{

            //    customerName = "daohangshuxing",

            //    customerDate = DateTime.Now

            //};

            //customerInfo.OrderInfoes.Add(new OrderInfo()

            //{

            //    orderName = "car1",

            //});

            //customerInfo.OrderInfoes.Add(new OrderInfo()

            //{

            //    orderName = "car2"

            //});

            //dbContext.Set<CustomerInfo>().Add(customerInfo);

            //dbContext.SaveChanges();

            #endregion

            #region 查询LINQ Lambda表达式 EF

            //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());

            ////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());

            ////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());

            ////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());

            ////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());

            ////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);

            //}

            ////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());

            ////分页查询 lambda特有

            //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());

            #endregion

            #region Lambda 分页封装

            //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());

            #endregion

            Console.WriteLine("OK");

            Console.ReadKey();

        }

        //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 - ))

                .Take(pageSize);

            return rows;

        }

    }

}

EF查询Demo源代码

参考链接：

ASP.NET MVC EF直接更新数据(不需查询)：http://www.cnblogs.com/Dr-Hao/p/5255630.html

ASP.NET EF 使用LinqPad 快速学习Linq：http://www.cnblogs.com/Dr-Hao/p/5357112.html

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