Python: Best approach to storing object state in database?

Question

I need to store instances (or at least their state) in a database. The idea is that I should be able to re-create the instance on demand. Since I define the classes, I can choose how I would like to store the data.

Consider the following diagram, inheritance diagram:

                    A
                   / \
                  B   C
                 /\   /\
                D  E F  ...

The idea is that the instance can belong to any of those classes and can itself store other objects (that I have completely design control over).

My first thought is to store the state exclusively in a dictionary, dump the dictionary into a json and store it in the database. At run time, load json from the database convert it to dictionary, create an object passing in the dictionary that get's setup and so on...

I'm not sure if that is a good approach, and also if there are any other issues that might crop up. I already came across one, where if you use myobj.dict you don't actually get all the class' parent's attributes though...

Any suggestions?

Does it have to be a database? One simple dumb solution is to just pickle them to a file. — Daenyth, Nov 04 '11 at 19:07
http://www.python.org/workshops/1997-10/proceedings/shprentz.html — Robert Harvey, Nov 04 '11 at 19:07
No constraints? Have you thought about using pickle/unpickle? — muratgu, Nov 04 '11 at 19:09

gomad · Accepted Answer · 2011-11-04T20:20:03.717

4

There are several approaches. I don't really think we can tell you from the information you've provided what the best approach for you is.

You can use an ORM, like SQLAlchemy.
You can use an object database.
You could pickle your objects and store them in any relational database or datastore including shelve, which is included in the standard distribution.

These are the approaches I can think of off the top of my head. Only you can determine which one(s) fit your requirements and intention best.

edited Nov 04 '11 at 20:20

answered Nov 04 '11 at 19:10

gomad

1,029
7
16

This is a good answer. It should also mention *shelve* which has a near-zero learning curve and is included in the standard library (no third-party module installs required). – Raymond Hettinger Nov 04 '11 at 19:13
@RaymondHettinger - You are correct. I guess I considered it part of the third option, but I will edit it to reflect *shelve*, thank you. – gomad Nov 04 '11 at 20:18
1

I ended up going with zodb for my needs, albeit shelve likely would have worked as well, but doesn't seem to be intended for very large data sets. – noobzie Nov 06 '11 at 17:51

score 2 · Answer 2 · answered Nov 04 '11 at 19:11

2

The shelve module is the easiest way to get started with storing instances retrievable by a key. It automatically pickles and unpickles for you and takes care of the reading and writing to a file.

answered Nov 04 '11 at 19:11

Raymond Hettinger

216,523
63
388
485

score 0 · Answer 3 · edited May 23 '17 at 11:47

0

My suggestion would be to design an Object model around your states and use an ORM toolkit for Python. Several are mentioned here - What are some good Python ORM solutions?

I believe its not best to re-invent the wheel. You can use an ORM toolkit to either store the states or the actual object instance tree itself.

edited May 23 '17 at 11:47

Community

1
1

answered Nov 04 '11 at 19:08

Danish

3,708
5
29
48

Python: Best approach to storing object state in database?

3 Answers3