如何在 n 层架构中解决这个 NHibernate 查询? [英] How can I solve this NHibernate Querying in an n-tier architecture?

问题描述

我在尝试将 NHibernate 与我的服务层分离时遇到了障碍.我的架构如下所示:

I've hit a wall with trying to decouple NHibernate from my services layer. My architecture looks like this:

web -> services -> repositories -> nhibernate -> db

web -> services -> repositories -> nhibernate -> db

我希望能够从我的服务层和可能是我的 web 层生成 nhibernate 查询，而这些层不知道它们正在处理什么orm.目前，我的所有存储库都有一个 find 方法，它接受 IList标准.这允许我从架构中的任何位置传入一个标准列表，例如 new object() {"Username", usernameVariable};.NHibernate 接受它并创建一个新的 Criteria 对象并添加传入的标准.这适用于我的服务层的基本搜索，但我希望能够传入我的存储库转换为 NHibernate 标准的查询对象.

I want to be able to spawn nhibernate queries from my services layer and possibly my web layer without those layers knowing what orm they are dealing with. Currently, I have a find method on all of my repositories that takes in IList<object[]> criteria. This allows me to pass in a list of criteria such as new object() {"Username", usernameVariable}; from anywhere in my architecture. NHibernate takes this in and creates a new Criteria object and adds in the passed in criteria. This works fine for basic searches from my service layer, but I would like to have the ability to pass in a query object that my repository translates into an NHibernate Criteria.

真的，我很想实现类似于这个问题中描述的内容:抽象nhibernate标准是否有价值.我只是没有找到关于如何实现这样的东西的任何好的资源.该问题中描述的方法是一种好方法吗?如果是这样，任何人都可以提供一些有关如何实施此类解决方案的指示吗?

Really, I would love to implement something like what is described in this question: Is there value in abstracting nhibernate criterion. I'm just not finding any good resources on how to implement something like this. Is the method described in that question a good approach? If so, could anyone provide some pointers on how to implement such a solution?

推荐答案

抽象掉 ORM 将:

• 为重新定义其 API 带来了大量工作
• 无法优化/批量数据库访问
• 让理解所执行的查询变得更加困难
• 将导致大量的 SELECT N+1

而且所有的价值都很少:交换 ORM 框架的模糊选项，很可能会有很多其他问题

and all for very little value: the vague option to exchange the ORM framework which will most probably have a lot of other problems

• 缺少功能
• 实现上的细微差别
• 学习曲线

更新:经验

我曾经参与实现现有 DAL 抽象的新提供者.它最终表现不佳，引入了很多错误，错误处理是一团糟，有时会使用陈旧数据，因为应用程序采用默认实现.原因:

I was once involved in implementing a new provider of an existing DAL abstraction. It ended up performing badly, introduced a lot of bugs, Errorhandling was a mess and sometimes used stale data because the application assumed the default implementation. Reasons:

• 缓存不知道上下文
• 缓存实现有不同的语义
• 批处理 API 差异太大而无法抽象
• 错误特定于实现(例如，FileNotFound -> FilesearchDialog 对于基于 tcp/ip 的数据库是无用的)
• 错误恢复是不同的(每个实现都有自己的一组可以从中恢复的错误)
• 锁定机制不同
• SQL 数据库中没有一致的更改事件
• 嵌套事务
• 模型类中的默认实现被破坏
• 重新实现所有抽象的查询需要大量的工作，并引入了很多复制粘贴错误
• 未明确说明顺序的查询将在不同的实现中返回不同的排序结果

• Caching does not know context
• Cacheimlementation had different semantics
• batching APIs too different to be abstracted
• Errors are specific to implementation (e.g. FileNotFound -> FilesearchDialog is uselesss for a tcp/ip based databases)
• Error recovery is different (each implementation has it's own set of errors it can recover from)
• locking mechanism was different
• no consistent change event in SQL-Databases
• nested transactions
• default implementation bleeded in Model classes
• reimplementing all abstracted Queryies was a lot of work and introduced a lot of copy paste bugs
• querying without explicitly stating the order will return different ordered results in different implementations

对应用程序进行了大量重构:

It took a lot of refactoring of the application:

• 去除仅一种实现提供的功能
• 每个实现的缓存管理
• 由于瞬态数据导致的包装器身份问题
• 非常努力地实现对两个数据存储的查询

附加点:

• 通过抽象 DAL 迁移数据的速度慢得要命
• 实现另一个实现永远不会发生，因为上述问题太昂贵了(在提到的场景中，我们开始慢慢重新实现整个项目)
• 实现 DAL API 的正确语义极其困难，因为在纯 API 中没有使用上下文

移植(业务任务)在 IMO 中会少很多痛苦，因为我们为了性能而做了一些.

Porting (of business tasks) would have been a lot less painfull IMO as we did that for a few because of performance.

更新 2:经验 2:尝试从 NHibernate 移植到 EntityFramework 时遇到障碍(使用 NH 实现，但无法在合理时间内使用 EF 4)

Update2: experience2: RoadBlocks while trying to port from NHibernate to EntityFramework (impl with NH but couldn't with EF 4 in reasonable time)

• 嵌套事务
• 枚举支持
• 带有compositeId 的引用(如何去掉referenceId)
• 组件中的引用
• 读取批处理(Futures)，一次性完成页面 + 计数
• 映射 CultureInfo(IUserType 支持)

这篇关于如何在 n 层架构中解决这个 NHibernate 查询?的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！