meuhdb 0.3.0

MeuhDB, a database that says

The database that says “Meuh”

MeuhDb is a “dummy” key / JSON value store written in Python.

Install

To install the latest release:

pip install meuhdb

… but since this is a very early release, you’d better stick to this Github source repository. You may want to read the Changelog, too.

Basic usage

>>> from meuhdb import MeuhDb
>>> db = MeuhDb()  # Create in-memory database
>>> db.set('one', {'name': 'Alice', 'good': True, 'chief': True})
>>> db.set('two', {'name': 'Bob', 'good': True})
>>> db.set('three', {'name': 'Carl', 'good': False})
>>> db.filter(name='Alice')
{'one': {'chief': True, 'good': True, 'name': 'Alice'}}
>>> db.filter(good=True)
{'two': {'good': True, 'name': 'Bob'}, 'one': {'chief': True, 'good': True, 'name': 'Alice'}}
>>> db.filter(good=True, chief=True)  # More than one criteria, it's a "AND"
{'one': {'chief': True, 'good': True, 'name': 'Alice'}
>>> db.delete('one')
>>> db.filter(name='Alice')
{}
>>> db.exists('one')
False
>>> db.insert({'name': 'John'})
'eb3c3a1d-8999-4052-9e3c-2f3542c047b1'
>>> db.update('eb3c3a1d-8999-4052-9e3c-2f3542c047b1', {'age': 42})
>>> db.get('eb3c3a1d-8999-4052-9e3c-2f3542c047b1')
{'age': 42, 'name': 'John'}

At the moment, you can only query on “equalities”, i.e. a strict equality between what you’re looking for and what’s in the JSON fields (no special operator: greater than, different, etc).

The values must be JSON serializable values (dictionaries, does not work with dates, datetimes, sets, etc.)

Database creation

There are a few optional parameters with the MeuhDb class constructor:

MeuhDb(
  path=None,
  autocommit=False, autocommit_after=None,
  lazy_indexes=False,
  backend=DEFAULT_BACKEND)

• path: is the file path of your JSON database if you want to save it to a file. If the file already exists, MeuhDb tries to load its data. If it’s not provided, the DB will be in-memory.

• autocommit: if set to True, every “write” operation will be transmitted to the file. It can be I/O consuming, since the whole DB is written on the disk every time.

• autocommit_after: A numeric value. If set, the database will be committed every “n” write operations. Bear in mind that if the autocommit flag is set, it has priority over the counter.

• lazy_indexes: When set to True, when the DB is written to the database, only the definition of the indexes is stored, not the index values themselves. This means the DB is faster at writing times, but will load slower, because we’ll need to rebuild all indexes,

• backend: chose which JSON backend you can use. There are 3 backends possible, from the least efficient, to the best one: “json” (from the standard lib), “simplejson”, “jsonlib”, “yajl”, or “ujson”. MeuhDb will try to load each one of them and make them available if you want. The DEFAULT_BACKEND value will take the most performing backend value available. If you provide an unavailable backend, don’t worry, MeuhDb will fallback to the comfortable `json from the standard library.

Example:

>>> db = MeuhDb('hello.json', autocommit=False, backend='ujson')
>>> db.set('1', {'name': 'Alice'})  # data is not on disk
>>> db.commit()  # saves to disk
>>> db = MeuhDb('hello.json', autocommit=True)
>>> db.all()  # Data is reloaded from the disk
{u'1': {u'name': u'Alice'}}
>>> db.set('2', {'name': 'Bob'})  # data is written on disk

Indexes

MeuhDb supports index creation. You can index one or more fields to accelerate queries.

Example:

>>> db.create_index('name')
>>> db.filter(name='Alice')  # Will use this index

• You don’t have to index all the fields available in your JSON values, only the one you may query on.

• Indexes will be saved on commit() along with the Database.

• if somehow the index is screwed up, simply create it with the recreate argument: db.create_index('name', recreate=True).

Index types

You can specify the index type using this:

db.create_index('name', _type='lazy')

You can only create two types of indexes: default or lazy. Lazy indexes will not be stored when the database is committed, and will be reloaded at startup. You can mix default and lazy indexes.

Note: since all JSON key should be strings, you can’t obviously store indexes with non-string values. As soon as an index receives a non-string value (an int or a boolean, for example), it’ll be changed into a lazy index.

Warnings

This is not a real actual ACID-ready database manager. This will probably suit a “one-user-only” use case. Opening an loading a large file is very I/O consuming. So MeuhDb will never replace a proper NoSQL database system.

Hack

MeuhDb will work with a standard Python 2 distribution. (I’ve got plans to make it Python-3-ready)

Inside a virtualenv, simply clone this repository and install it in dev mode:

git clone https://github.com/brunobord/meuhdb.git
cd meuhdb
pip install -e ./

You may want to install one or more of these packages to be able to pick one of these enhanced backends:

• simplejson,

• jsonlib (or jsonlib-python3),

• yajl,

• ujson

To run the tests, you’ll have to install tox (pip install tox) and simply run the command tox.

Todo

A lot of things are missing. The Github issues list will work as a “todo list”. If you have any bug report, suggestion, please do.

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License

This software is published under the terms of the MIT License See the LICENSE file for more information.