Lerning Entity Framework 6 ------ Working with in-memory data

最新推荐文章于 2025-09-11 20:53:34 发布

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最新推荐文章于 2025-09-11 20:53:34 发布

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文章标签：数据库

原文链接：http://www.cnblogs.com/zzy0471/p/6854906.html

本文介绍如何使用Entity Framework在已加载到内存的数据中进行查询，而不是每次都从数据库中获取。通过对比两种查询方式，展示了如何利用Entity Framework的特性提高查询效率。

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