GreenDao多对多关系 [英] GreenDao Many to Many Relation

问题描述

我用Greendao在我的Andr​​oid数据库映射。到目前为止，一切都很正常。

I use Greendao for my database mapping in Android. So far everything works great.

但现在我有以下问题：

我有一个群集和叶对象。一个集群包含许多叶对象。
如果群集被放大它可以在更多的集群和多叶分手了。这并不是一个严格的树关系更是一个大簇具有大量的叶子，但一小簇可具有这样叶子的子集。

I have a Cluster and leaf Objects. A cluster contains many leaf objects. If a cluster is zoomed it can split up in more clusters and more leafs. This is not a strict tree relationship it is more that a big cluster has a lots of leafs but a small cluster can have a subset of this leafs.

基本上是一个群集有很多叶子，但叶子也都在多个群集，因为叶子的ID是唯一的，关系到集群保存在叶叶只能在一个集群吧？

Basically a cluster has many leafs but leafs also are in multiple clusters, since the id of a leaf is unique and the relation to the cluster is saved in the leaf a leaf can only be in one cluster right?

该greendao主页指出，多对多的关系是可能的，但我怎么也无法让我的头围绕它如何将这种关系模型。

The greendao homepage states that many to many relations are possible but how i can't get my head around it how to model this relation.

是否可以模拟这种关系或者是数据结构GreenDao问题？

Is it possible to model such a relation or is the data structure a problem for GreenDao?

推荐答案

让我们开始从报价文档：

虽然greenDAO不支持N：直接米的关系，截至目前，你
  可以模拟连接表作为一个独立的实体。在实践中，你经常
  有关系实体有额外的属性，所以你可能要
  这样做的反正。在未来的版本中，greenDAO可能直接引入
  支持的n：M关系

While greenDAO does not support n:m relations directly as of now, you can model the join table as a separate entity. In practice, you often have "relation entities" with additional properties, so you might want to do so anyway. In future releases, greenDAO might introduce direct support of n:m relations.

所以，你的情况，你必须一个实体模型，即集群与叶之间。让我们把这个实体ClusterLeaf。为了有效地查询叶子为群集，我建议原查询的，因为QueryBuilder的不支持加入呢。

So, in your case you have to model an entity, that is between Cluster and Leaf. Let's call this entity ClusterLeaf. To query leafs for a cluster efficiently, I'd suggest raw queries because the QueryBuilder does not support joins yet.

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