问题
I have a web application built on an MVC design.
I have a database which contains a large number of objects (forum threads) which I can't load into memory at once. I now want to display (part of) this collection with different filters in effect (kinda like what stackoverflow does with questions sorted by date, votes, tags etc).
Where do I implement the filtering logic? It seems to me that this must go into the model part of the application, as only models interact with the database (in my implementation). If I make the filtering a part of the view, then the view must access the database directly to get the list of filtered objects, right? I'd like to avoid this, because it exposes the database layout to the view. But at the same time, displaying different views of the same data should be implemented in the view part of the application, as they are just that -- different views of the same data.
So how do I resolve this? Do I create an additional model, say, FilteredThreadsList, and have it remember the filter to use, and then use a FilteredView to display the list of threads that FilteredThreadsList spits out?
Or do I have to build a ThreadQueryier that allows views to query the database for certain thread objects, so I can have the filtering logic in a view without exposing the database backend?
回答1:
From an architectural point of view, the model should be having the code for filtering. This is so, because in many applications the code for filtering is not trivial and has a good amount of domain logic in it. (Think of filtering top gainers from a list of stocks). From your example as well, it looks the same since you might want to filter by vote or by date or by tags and then by answered or unanswered etc.
In some very simple applications that deal with search/list of entities and allows Create/Read/Update/Delete of an entity, the pagination, sorting and filtering logic is usually very generic and can be implemented in a controller base class that is inherited by all entity-specific controller classes.
The bottom line is this: if your filtering logic is generic put it in the controller else put it in the model.
回答2:
You should never query data from the view. I don't know what framework you are using in particular but as for Ruby on Rails (should be the same for other frameworks) we always pull the necessary data from the controller and store all that information into a variable. The variable will be accessed by the view which can help you avoid querying your database directly from the view.If the code to query the database gets too lengthy in the controller, insert that code into the model instead so it's more maintainable for your project in the future. Additionally, you can call this model method from multiple places in your application if needed. Good luck!
回答3:
Model, that's only bunch of entities.
View provides a visual representation of the data from model - use as much of views as you want. If your application is web based, you can fetch data into browser just once (AJAX) using and re-use them for different UI components rendered in the browser.
As for what entities and what view to use for their representation, I think it's work of Controller. If you need some support for it on "model layer", add it but avoid tight coupling.
来源：https://stackoverflow.com/questions/5209615/in-a-mvc-web-application-who-is-responsible-for-filtering-large-collections-of