Entity FrameWork 操作使用详情

Entity FrameWork 是以ADO.net为基础发展的ORM解决方案。

一、安装Entity FrameWork框架

二、添加ADO.Net实体数据模型

三、EF插入数据

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //获取数据库上下文对象
            testContext dbContext = new testContext();
            //创建数据实体
            employee emp = new employee
            {
                name = "yangs",
                passwd = "123",
                age = 18
            };
            dbContext.employee.Add(emp);
            //提交数据
            dbContext.SaveChanges();

            Console.WriteLine(emp.id);
            Console.ReadKey();
        }
    }
}

四、EF删除数据

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //获取id
            employee emp = new employee
            {
                id = 18
            };
            //获取数据库上下文对象
            testContext dbContext = new testContext();
            //将实体添加到数据库上下文
            dbContext.employee.Attach(emp);
            //对数据删除
            dbContext.employee.Remove(emp);
            //保存
            dbContext.SaveChanges();

        }
    }
}

五、EF修改数据

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            //准备实体
            employee emp = new employee
            {
                id = 11,
                name = "例子",
                passwd = "123",
                age = 44
            };
            //获取数据库上下文对象
            testContext dbContext = new testContext();
            //将实体添加到数据库上下文
            dbContext.employee.Attach(emp);
            dbContext.Entry(emp).State = System.Data.Entity.EntityState.Modified;
            dbContext.SaveChanges();
        }
    }
}

六、EF 查询数据

1.简单查询

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            testContext dbContext = new testContext();
            var list = dbContext.employee;
            foreach (var item in list)
            {
                Console.WriteLine(item.name);
            }
            Console.ReadKey();
        }
    }
}

2.where 查询条件

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            testContext dbContext = new testContext();
            var list = dbContext.employee.Where(p => p.id > 5);
            foreach (var item in list)
            {
                Console.WriteLine(item.name);
            }
            Console.ReadKey();
        }
    }
}

2. skip(10) => 逃过10条数据，take(10) => 获取10条数据

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            testContext dbContext = new testContext();
            var list = dbContext.employee.Skip(1).Take(2);
            foreach (var item in list)
            {
                Console.WriteLine(item.name);
            }
            Console.ReadKey();
        }
    }
}

 3. orderBy 排序

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            testContext dbContext = new testContext();
            //降序
            var list = dbContext.employee.OrderByDescending(p => p.id);
            foreach (var item in list)
            {
                Console.WriteLine(item.name);
            }
            Console.ReadKey();
        }
    }
}

4. select 查询某几个字段

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            testContext dbContext = new testContext();
            //降序
            var list = dbContext.employee.Select(p => new { p.id, p.name }).Where(p => p.id > 5);
            foreach (var item in list)
            {
                Console.WriteLine(item.id+" -- "+item.name);
            }
            Console.ReadKey();
        }
    }
}

5. EF高级写法

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            testContext dbContext = new testContext();
            //降序
            var list = from o in dbContext.employee where o.id > 5 select o; 
            foreach (var item in list)
            {
                Console.WriteLine(item.id+" -- "+item.name);
            }
            Console.ReadKey();
        }
    }
}

join 联合查询

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            testContext dbContext = new testContext();
            //降序
            var list = from e in dbContext.employee
                       join i in dbContext.employeeInfo
                       on e.id equals i.emp_id
                       where e.id > 5 
                       select new {e, i.content};
        }
    }
}

 七、延迟加载

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Threading.Tasks;

namespace EFDemo
{
    class Program
    {
        static void Main(string[] args)
        {
            testContext dbContext = new testContext();
            //降序
            var list = dbContext.employee.ToList();

            foreach (var item in list)
            {
                
            }
        }
    }
}

toList()转换为本地内存数据级别，会请求数据。如果没有toList()，则当数据遍历的时候请求。