在实体框架中加载具有过滤条件的子对象记录

Posted 2023-04-12

【中文标题】在实体框架中加载具有过滤条件的子对象记录

【英文标题】：Load child object records with filter condition in Entity Framework

【发布时间】：2013-08-10 17:04:08

【问题描述】：

使用实体框架设计数据访问层，PackageInstance对象的示例POCO结构为

public class PackageInstance

  public virtual long PackageInstanceId set;get;
  public virtual boolean IsDeleted set;get;
  public virtual List<Session> Sessions set;get;


public class Session

  public virtual long SessionId set;get;
  public virtual long PackageInstanceId set;get;
  public virtual boolean IsDeleted set;get;
  public virtual List<Note> Notes set;get;


public class Note

  public virtual long NoteId set;get;
  public virtual long SessionId set;get;
  public virtual boolean IsDeleted set;get;
  public virtual List<Documents> Document set;get;

我需要在单个方法调用中加载 PackageInstance 对象及其子对象，而不是单独加载每个对象。

  var packageInstanceDB = entity.PackageInstances.First(p => p.PurchaseSessionId == purhcaseSessionId);                   
  //There is a DB call happening here to load the Session.
  packageInstanceDB.Sessions.Where(s=>!s.IsActive).ForEach(s => 
  
       //Again there is a DB call happening here to load the associated session notes.
       s.Notes.Where(sn => !sn.IsDeleted).ToList().ForEach(sd=>
       //Again there is a DB call happening here to load the associated note documents.
       sd.Documents.Where(doc=>!doc.IsDeleted));
  );

这里如何消除多个DB调用？

【问题讨论】：

你的代码被编译了吗？

强乐。用实际的代码快照更新了问题。这里也发生了多个数据库调用。

你能给我们举个例子并解释一下你想得到什么吗？

【参考方案1】：

免责声明：我是项目的所有者Entity Framework Plus

EF+ Query IncludeFilter 功能允许过滤相关实体。支持EF5

var packageInstanceDB = entity.PackageInstances
    .IncludeFilter(x => x.Sessions)
    .IncludeFilter(x => x.Sessions.Select(y => y.Notes.Where(sn => !sn.IsDeleted)))
    .IncludeFilter(x => x.Sessions.SelectMany(y => y.Notes.Where(sn => !sn.IsDeleted)).Select(z => z.Documents.Where(sn => !sn.IsDeleted)))
    .First(p => p.PackageInstanceId == purhcaseSessionId);

注意：必须包含每个路径

维基：EF+ Query IncludeFilter

【讨论】：

首先要感谢 Jonathan Magnan... 4 个月前，我用 EFP 替换了现有代码，它提供了更好的性能.....