Skip to content

SQLAlchemy Base class

SQLAlchemy Base

The SQLAlchemy DeclarativeBase class is the "base" class all of your SQLalchemy table model classes should inherit from. When describing a new entity, you intialize the class like:

Initialize table class
1
2
3
4
...

class SomeTableModel(Base):
    ...

When you use SQLAlchemy to create the table metadata, the Base class gathers all models that inherit from the same Base instance and creates table structures in your database.

Example base.py

In your project, you can put your SQLAlchemy DeclarativeBase code in a file, i.e. app_name/database/base.py, so it can be imported throughout the rest of your app.

Declare SQLAlchemy Base (example base.py)
 1
 2
 3
 4
 5
 6
 7
 8
 9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
56
57
58
"""SQLAlchemy `DeclarativeBase`, `MetaData`, and `registry` objects.

Import this `Base` into SQLAlchemy model files and let classes inherit from
the `DeclarativeBase` declared here.

The `registry()` function sets the global SQLAlchemy `registry` for the `DeclarativeBase` object.

!!! note

    Docs for `DeclarativeBase` and `registry()`

    - [Using a DelcarativeBase base class](https://docs.sqlalchemy.org/en/20/orm/declarative_styles.html#using-a-declarative-base-class)

    Docs for MetaData object

    - [Unified tutorial](https://docs.sqlalchemy.org/en/20/tutorial/metadata.html#tutorial-working-with-metadata)
    - [MetaData Docs](https://docs.sqlalchemy.org/en/20/core/metadata.html)
    - [Impose a table naming scheme with MetaData object](https://docs.sqlalchemy.org/en/20/core/metadata.html#specifying-a-default-schema-name-with-metadata)

"""

from __future__ import annotations

import sqlalchemy as sa
import sqlalchemy.orm as so

## Global SQLAlchemy MetaData object
metadata: sa.MetaData = sa.MetaData()

## Registry object stores mappings & config hooks
reg = so.registry()


## SQLAlchemy DeclarativeBase is the parent class object table classes will inherit from
class Base(so.DeclarativeBase):
    """Default/Base class for SQLAlchemy models.

    Description:

    Child classes inheriting from this Base object will be treated as SQLAlchemy
    models. Set child class tables with `__tablename__ = ....`

    Global defaults can be set on this object (i.e. a SQLAlchemy registry), and will
    be inherited/accessible by all child classes.

    !!! note

        When this class is instantiated, it will not be of type sqlalchemy.orm.DeclarativeBase;
            Because of the way this class is intialized, its type will be
            sqlalchemy.orm.decl_api.DeclarativeAttributeIntercept

    Params:
        registry (sqlalchemy.Registry): A `registry` object for the `Base` class
        metadata (sqlalchemy.MetaData): A `MetaData` object, with data about the `Base` class
    """

    registry: so.registry = reg
    metadata: sa.MetaData = metadata