Models and Fields - Model options and table metadata - 《Peewee 3.5.0 Documentation》

Model options and table metadata
- Meta.primary_key

Model options and table metadata

In order not to pollute the model namespace, model-specific configuration is placed in a special class called Meta (a convention borrowed from the django framework):

from peewee import *
contacts_db = SqliteDatabase('contacts.db')
class Person(Model):
    name = CharField()
    class Meta:
        database = contacts_db

This instructs peewee that whenever a query is executed on Person to use the contacts database.

Note

Take a look at the sample models - you will notice that we created a BaseModel that defined the database, and then extended. This is the preferred way to define a database and create models.

Once the class is defined, you should not access ModelClass.Meta, but instead use ModelClass._meta:

>>> Person.Meta
Traceback (most recent call last):
  File "<stdin>", line 1, in <module>
AttributeError: type object 'Person' has no attribute 'Meta'
>>> Person._meta
<peewee.ModelOptions object at 0x7f51a2f03790>

The ModelOptions class implements several methods which may be of use for retrieving model metadata (such as lists of fields, foreign key relationships, and more).

>>> Person._meta.fields
{'id': <peewee.PrimaryKeyField object at 0x7f51a2e92750>,
 'name': <peewee.CharField object at 0x7f51a2f0a510>}
>>> Person._meta.primary_key
<peewee.PrimaryKeyField object at 0x7f51a2e92750>
>>> Person._meta.database
<peewee.SqliteDatabase object at 0x7f519bff6dd0>

There are several options you can specify as Meta attributes. While most options are inheritable, some are table-specific and will not be inherited by subclasses.

Option	Meaning	Inheritable?
`database`	database for model	yes
`table_name`	name of the table to store data	no
`table_function`	function to generate table name dynamically	yes
`indexes`	a list of fields to index	yes
`primary_key`	a `CompositeKey` instance	yes
`constraints`	a list of table constraints	yes
`schema`	the database schema for the model	yes
`only_save_dirty`	when calling model.save(), only save dirty fields	yes
`options`	dictionary of options for create table extensions	yes
`table_alias`	an alias to use for the table in queries	no
`depends_on`	indicate this table depends on another for creation	no
`without_rowid`	indicate table should not have rowid (SQLite only)	no

Here is an example showing inheritable versus non-inheritable attributes:

>>> db = SqliteDatabase(':memory:')
>>> class ModelOne(Model):
...     class Meta:
...         database = db
...         table_name = 'model_one_tbl'
...
>>> class ModelTwo(ModelOne):
...     pass
...
>>> ModelOne._meta.database is ModelTwo._meta.database
True
>>> ModelOne._meta.table_name == ModelTwo._meta.table_name
False

Meta.primary_key

The Meta.primary_key attribute is used to specify either a CompositeKey or to indicate that the model has no primary key. Composite primary keys are discussed in more detail here: Composite primary keys.

To indicate that a model should not have a primary key, then set primary_key = False.

Examples:

class BlogToTag(Model):
    """A simple "through" table for many-to-many relationship."""
    blog = ForeignKeyField(Blog)
    tag = ForeignKeyField(Tag)
    class Meta:
        primary_key = CompositeKey('blog', 'tag')
class NoPrimaryKey(Model):
    data = IntegerField()
    class Meta:
        primary_key = False