EntityFramework优于LinqToSQL的小知识点

Find方法：

 

        //Find方法
        //用于通过主键查找单个对象。
        //优点：Find会首先在Context的缓存中查找，如果查找到，则直接返回，避免的数据库的查询。FirstOrDefault会始终进行数据库查询，而不管缓存中是否已经存在
        Guid actionItemId = Guid.NewGuid();
        ActionItem actionItem = context.ActionItems.Find(actionItemId);

 

Include方法

        //Include方法（首先引用System.Data.Entity命名空间）
        //用于进行一次查询，便将相关的对象都一次性查找到。
        //优点：可极大地减少数据库查询次数，极大地提高页面性能。
        IEnumerable<ActionItem> actionItems = context.ActionItems
            .Include(item => item.Histories)
            .Include(item => item.ActionItemMembers)
            .Where(item => item.AssigneeId == this.User.Identity.Name);

        //以下是MSDN对Include的用法的描述
        //To include a single reference: query.Include(e => e.Level1Reference).
        //To include a single collection: query.Include(e => e.Level1Collection).
        //To include a reference and then a reference one level down: query.Include(e => e.Level1Reference.Level2Reference).
        //To include a reference and then a collection one level down: query.Include(e => e.Level1Reference.Level2Collection).
        //To include a collection and then a reference one level down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Reference)).
        //To include a collection and then a collection one level down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Collection)).
        //To include a collection, a reference, and a reference two levels down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Reference.Level3Reference)).
        //To include a collection, a collection, and a reference two levels down: query.Include(e => e.Level1Collection.Select(l1 => l1.Level2Collection.Select(l2 => l2.Level3Reference))).

 

EntityFunctions类

        //EntityFunctions类（首先引用System.Data.Objects命名空间）
        //有些Linq To Entity不支持的查询，需用EntityFunctions里的方法
        context.ActionItems.Where(item => EntityFunctions.TruncateTime(item.CreateTime) == DateTime.Today);