ASP.NET EF(LINQ/Lambda查询)

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

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] > 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 - 1))
                .Take(pageSize);
            return rows;
        }
    }
}

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