最佳实践:带有Room和LiveData的运行时筛选器 [英] Best practice: Runtime filters with Room and LiveData

问题描述

我正在处理一个屏幕，该屏幕显示了使用回收站的Room包装的DB的内容.适配器从ViewModel获取LiveData，该ViewModel隐藏对Room DAO对象的查询调用.因此，LiveData对象实际上是一个ComputableLiveData对象，它知道Room DB的更改.

I am working on a screen that shows the contents of a Room wrapped DB using a recycler. The adapter gets the LiveData from a ViewModel that hides the query call on the Room DAO object. So, the LiveData object is actually a ComputableLiveData object that is aware of changes to the Room DB.

现在，我想在屏幕上添加过滤器选项.在此Room-LiveData-ViewModel设置中，我将在哪里/如何实现它?

Now I want to add filter options to the screen. Where / how would I implement this in this Room-LiveData-ViewModel setup?

适配器或ViewModel是否应在LiveData中对结果进行后置过滤"?是否应针对每个过滤器更改从房间中重新查询数据?我可以为此重用基础的(可计算的)LiveData吗?如果没有，我是否真的应该为每个过滤器更改创建新的LiveData?

Should the adapter or ViewModel "postfilter" the results in the LiveData? Should I requery the data from room for every filter change? Can I reuse the underlying (Computable)LiveData for that? If not, should I really create new LiveData for every filter change?

此处讨论了类似的问题:重新加载RecyclerView使用Room，ViewModel和LiveData更改数据后

A similar question is discussed here: Reload RecyclerView after data change with Room, ViewModel and LiveData

推荐答案

所以，我最终这样做了:

So, I ended up doing it like this:

• 该片段将过滤器状态转移到ViewModel.副作用:多个片段实例可能会使用过滤器状态(即由于配置更改而导致后续使用).也许您想要那样，也许不需要.我知道.
• ViewModel包含一个MediatorLiveData实例.它只有一个来源:Room DB LiveData对象.消息源只是预示着要更改调解员.如果过滤器被片段更改，则源将被重新查询交换.

回答我的详细问题:

• 不进行后过滤
• 是的，重新查询过滤器更改
• 我不会重用ComputableLiveData(不确定是否可以使用)

关于评论中的讨论:

• 我不应用分页

关于会议室的最后说明:我错了吗?或者我需要为我要应用的每个过滤器组合编写单独的DAO方法吗?好的，我可以通过String插入select语句的可选部分，但是那样我会失去Room的好处.某种使语句可组合的语句生成器会很好.

Final note on Room: Am I wrong or do I need to write seperate DAO methods for every filter combination I want to apply? Ok, I could insert optional parts of the select statement via a String, but then I would lose the benefits of Room. Some kind of statement builder that makes statements composable would be nice.

请注意下面Ridcully的评论.他提到了SupportSQLiteQueryBuilder和@RawQuery来解决我猜的最后一部分.我还没有检查出来.

Please note the comment by Ridcully below. He mentions SupportSQLiteQueryBuilder together with @RawQuery to address the last part I guess. I didn't check it out yet though.

感谢 CommonsWare 和 pskink 为您提供帮助！

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