Best approach for tracking dependent state
- by Pace
Let's pretend I work on a project tracking application. The application is a database backed, server hosted, web application. In this application there are Projects which have many Activities which have many Tasks. A Task has two date fields an originalDueDate and a projectedDueDate.
In addition, there are dynamic fields on the Activities and the Projects which indicate whether the Activity or Project is behind schedule based on the projected due dates of the child tasks and various other variables such as remaining buffer time, etc.
There are a number of things that can cause the projectedDueDate to change. For example, an employee working on the project may (via a server request) enter in a shipping delay. Alternatively, a site may (via a server request) enter in an unexpected closure.
When any of these things occur I need to not only update the projectedDueDate of the Task but also trigger the corresponding Project and Activity to update as well.
What is the best way to do this?
I've thought of the observer pattern but I don't keep a single copy of all these objects in memory. When a request comes in, I query the Task in from the database, at that point there is no associated Activity in memory that would be a listener. I could remove the ability to query for Tasks and force the application to query first by Project, then by Activity (in context of Project), then by task (in context of Activity) adding the observer relationships at each step but I'm not sure if that is the best way.
I could setup a database event listening system so when a Task modified event is dispatched I have a handler which queries for the Activity at that point.
I could simply setup a two-way relationship between Task and Activity so that the Task knows about the parent Activity and when the Task updates his state the Task grabs his parent and updates state.
Right now I'm stuck considering all the options and am wondering if any single approach (doesn't have to be a listed approach) is jumping out at others as the best approach.
