pwiz, a model generator

pwiz is a little script that ships with peewee and is capable of introspecting an existing database and generating model code suitable for interacting with the underlying data. If you have a database already, pwiz can give you a nice boost by generating skeleton code with correct column affinities and foreign keys.

If you install peewee using setup.py install, pwiz will be installed as a “script” and you can just run:

python -m pwiz -e postgresql -u postgres my_postgres_db

This will print a bunch of models to standard output. So you can do this:

python -m pwiz -e postgresql my_postgres_db > mymodels.py
python # <-- fire up an interactive shell

>>> from mymodels import Blog, Entry, Tag, Whatever
>>> print [blog.name for blog in Blog.select()]

Command-line options

pwiz accepts the following command-line options:

The following are valid parameters for the engine (-e):

• sqlite
• mysql
• postgresql

pwiz examples

Examples of introspecting various databases:

# Introspect a Sqlite database.
python -m pwiz -e sqlite path/to/sqlite_database.db
# Introspect a MySQL database, logging in as root:secret.
python -m pwiz -e mysql -u root -P secret mysql_db_name
# Introspect a Postgresql database on a remote server.
python -m pwiz -e postgres -u postgres -H 10.1.0.3 pg_db_name

Full example:

$ sqlite3 example.db << EOM
CREATE TABLE "user" ("id" INTEGER NOT NULL PRIMARY KEY, "username" TEXT NOT NULL);
CREATE TABLE "tweet" (
    "id" INTEGER NOT NULL PRIMARY KEY,
    "content" TEXT NOT NULL,
    "timestamp" DATETIME NOT NULL,
    "user_id" INTEGER NOT NULL,
    FOREIGN KEY ("user_id") REFERENCES "user" ("id"));
CREATE UNIQUE INDEX "user_username" ON "user" ("username");
EOM
$ python -m pwiz -e sqlite example.db

Produces the following output:

from peewee import *
database = SqliteDatabase('example.db', **{})
class UnknownField(object):
    def __init__(self, *_, **__): pass
class BaseModel(Model):
    class Meta:
        database = database
class User(BaseModel):
    username = TextField(unique=True)
    class Meta:
        table_name = 'user'
class Tweet(BaseModel):
    content = TextField()
    timestamp = DateTimeField()
    user = ForeignKeyField(column_name='user_id', field='id', model=User)
    class Meta:
        table_name = 'tweet'

Observations:

• The foreign-key Tweet.user_id is detected and mapped correctly.
• The User.username UNIQUE constraint is detected.
• Each model explicitly declares its table name, even in cases where it is not necessary (as Peewee would automatically translate the class name into the appropriate table name).
• All the parameters of the ForeignKeyField are explicitly declared, even though they follow the conventions Peewee uses by default.

Note

The UnknownField is a placeholder that is used in the event your schema contains a column declaration that Peewee doesn’t know how to map to a field class.