如何在Sorm中为有多个孩子的实体建模?

问题描述

我有一个Workspace和Document实体，一个工作区可以包含零个，一个或多个文档的想法.我对此建模的第一种方法是:

I have a Workspace and Document entities, with the idea that a workspace can contain zero, one, or more documents. My first approach to model this was:

case class Workspace(name: String, documents: Seq[Document])

但是这不能很好地扩展，因为我的工作区可能包含许多个文档.幸运的是，我的业务需求使我能够分别处理工作空间和文档(从某种意义上说，当我拥有工作空间时，没有任何理由或不变性迫使我考虑其中包含的所有文档).

but this will not scale well since my workspaces may contain many documents. Fortunately, my business requirement allow me to treat workspaces and documents separately (in the sense that when I have a workspace, there is no reason or invariant that forces me to consider all documents contained in it).

问题::我想知道:如何在Workspace和Document ="nofollow"> Sorm ，这样我就可以在两者之间建立链接，而不必加载工作区的所有文档?我想象有一个存储库，该存储库将使我能够访问工作区的文档，并支持分页.)

Question: I am wondering: how would I model Workspace and Document in Sorm so that I have a link between the two but do not have to load all documents of a workspace? I imagine to have a Repository that would give me access to the documents of a workspace, with pagination support.)

case class Workspace(name: String)
case class Document(name: String, /* ... */)

trait WorkspaceRepository {
  def children(ws: Workspace, offset: Long, limit: Long)
}

推荐答案

轻松自如！您将它们定义为不相关:

Easy peasy! You define them unrelated:

case class Workspace ( name : String )
case class Document ( ... )

然后，您选择希望它们链接的方式.我看到两个.

Then you choose a way you wish them to be linked. I see two.

case class WorkspaceDocuments 
  ( workspace : Workspace, documents : Seq[Document] )

并获得工作区的所有文档，如下所示:

And get all documents of a workspace like so:

Db.query[WorkspaceDocuments]
  .whereEqual("workspace", theWorkspace)
  .fetchOne()
  .map(_.documents)
  .getOrElse(Seq())

在这种情况下，在实例声明中将workspace属性指定为唯一是有意义的:

In this case it makes sense to specify the workspace property as unique in instance declaration:

... Instance (
  entities = Set() +
             Entity[WorkspaceDocuments]( unique = Set() + Seq("workspace") )
  ...
)

Variant#2

case class WorkspaceToDocument
  ( workspace : Workspace, document : Document )

并像这样获取工作区的文档:

And get documents of a workspace like so:

Db.query[WorkspaceToDocument]
  .whereEqual("workspace", theWorkspace)
  .whereEqual("document.name", "...") // ability to filter docs
  .fetch()
  .map(_.document)

第一个变体不能让您过滤查询中的文档(至少在SORM v0.3.*中)，但是由于能够在工作空间上设置唯一约束，因此它在基于工作空间的查询上应该表现更好.第二种变体更加灵活，允许您应用各种过滤器.

First variant won't let you filter docs in your query (at least in SORM v0.3.*) but due to ability to set a unique constraint on a workspace it should perform better on workspace-based queries. The second variant is more flexible, allowing you to apply all kinds of filters.

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