zoukankan      html  css  js  c++  java
  • Lerning Entity Framework 6 ------ Working with in-memory data


    Sometimes, you need to find some data in an existing context instead of the database. By befault, Entity Framework always find data in database. If you want to find data which have loaded in memory, please do it like this:

    Frist of all, let's insert some data for testing:

    图片.png-8.2kB

    Then, Write some codes:

    class Program
    {
        static void Main(string[] args)
        {
            using (MyContext db = new MyContext())
            {
                var person = db.People.Find(1);
    
                var anotherPersons = db.People.Where(p => p.Age > 0);
                int count = anotherPersons.Count();
            }
    
            Console.ReadLine();
        }
    }
    
    public class Person
    {
        public int PersonId { get; set; }
    
        public int Age { get; set; }
    
        [MaxLength(50)]
        public string Name { get; set; }
    }
    
    public class MyContext:DbContext
    {
        public MyContext():base("name=Test")
        {
            DbInterception.Add(new MyCommandInterceptor());
        }
    
        public DbSet<Person> People { get; set; }
    }
    
    class MyCommandInterceptor : DbCommandInterceptor
    {
        public override void NonQueryExecuted(DbCommand command, DbCommandInterceptionContext<int> interceptionContext)
        {
            base.NonQueryExecuted(command, interceptionContext);
        }
    
        public override void ReaderExecuted(DbCommand command, DbCommandInterceptionContext<DbDataReader> interceptionContext)
        {
            base.ReaderExecuted(command, interceptionContext);
            Console.WriteLine("----------------------");
            Console.WriteLine(command.CommandText);
            Console.WriteLine();
    
        }
    
        public override void ScalarExecuted(DbCommand command, DbCommandInterceptionContext<object> interceptionContext)
        {
            base.ScalarExecuted(command, interceptionContext);
        }
    }
    

    Run the codes, you will find two SQL statments are excuted:

    图片.png-4.7kB

    Then, mondify the codes:

    static void Main(string[] args)
    {
        using (MyContext db = new MyContext())
        {
            var person = db.People.Find(1);
    
            var anotherPersons = db.People.Local.Where(p => p.Age > 0);
            int count = anotherPersons.Count();
        }
    
        Console.ReadLine();
    }
    

    Run it again:

    图片.png-3.2kB

    That's all.

  • 相关阅读:
    2019 CCSU GOLD!!!
    HDU 3397 Sequence operation(线段树区间染色加区间合并)
    浅谈线段树区间更新里的懒标记
    HDU 3308 LCIS(线段树区间合并)
    51Nod 1593 公园晨跑(RMQ,ST表)
    第四次作业
    lintcode-166-链表倒数第n个节点
    lintcode-163-不同的二叉查找树
    lintcode-162-矩阵归零
    lintcode-161-旋转图像
  • 原文地址:https://www.cnblogs.com/zzy0471/p/6854906.html
Copyright © 2011-2022 走看看