store and retrieve Vector in Android sqlite database

Question

Hello, I need to store an retrieve a vector of an unknown number of objects in an android sqlite database.

Essentially, the setup is this: I am developing a task management app, where the user can add as many notes as they like to their tasks. My current setup uses one database, with one row per task. This presents a problem when I need to associate multiple notes and their associated information with one task. I can see two approaches: try to store an array of notes or a vector or something as a BLOB in the task's row, or have another notes database in which each row contains a note and it's info, as well the id of the task which the note belongs to. This seems a little easier to implement, as all I would have to do to retrieve the data would be to get a cursor of all notes matching a particular id and then iterate through that to display them to the user. However, it seems a little inefficient to have a whole new database just for notes, and it makes syncing and deleting notes a little more difficult as well.

What do you think? Is it worth it to have a separate notes database? Should I use a BLOB or go for the separate database? If a BLOB, are there any good tutorials out there for storing and retrieving objects as BLOBs?

Answer 1

I think the answer to this question really lies in how you're going to go about updating things should they change. For now, the BLOB route probably seems like a really good idea, but what happens if you want to add some new functionality and you want to store some new property of notes (think of things like starred or importance). What would you need to do in order to update the notes object to add this new field? If it's just a database table, it's quite easy to change the layout of the table and even add a default value. If it's a BLOB, you're going to need to go through each entry, de-serialize the BLOB object, fix it, and re-serialize. That could get tricky.

Also, and this probably isn't as important to a small application using an embedded database, but it's easier to modify the database outside of the application if the object isn't a BLOB. Not to mention the queries you'll be able to write with the separate table. For example, how might someone calculate the number of notes that are attached to a task? If it's separated out in the database, it's a simple query.

Just my two cents.

Answer 2

It sounds like you need another table in your database (not another database). You already have a table for Tasks. Now make one for Notes. Make a column be a foreign key into the Tasks table. That is, Notes.Task_ID would hold the ID of the Task that the Note is for. Then when you want to get all of the notes for a task, query the Notes table.