sqlalchemy-mutables

A minimal package for nested mutable datatypes in SQLAlchemy. Main feature is a JSON field that is RFC-7159 compliant.

Developed for SQLAlchemy v1.3.24. Your mileage may very with other versions.

Installation

$ pip install sqlalchemy-mutables

Usage

from sqlalchemy_mutables import NestedMutableListColumn

class MyTable(Base):
    mutable_list = Column(NestedMutableListColumn)

from sqlalchemy_mutables import NestedMutableDictColumn

class MyTable(Base):
    mutable_dict = Column(NestedMutableDictColumn)

JSON

To be compliant with RFC-7159, 'primitives' need to be supported as top level values. These are values of type str|int|float|bool or None. Unfortunately, these types break SQLAlchemy Mutable functionality (specifically bool as this cannot be subclassed). To allow for these while maintaining mutable functionality for list and dict, a wrapper class has to be used via a hybrid_property.

from sqlalchemy_mutables import NestedMutableJSONColumn, NestedMutableJSONProperty

class MyTable(Base):
    _mutable_json = Column("mutable_json", NestedMutableJSONColumn)
    mutable_json = NestedMutableJSONProperty("_mutable_json")

It is possible to pass a custom functionality to the getter and/or setter:

def json_getter(value):
    if isinstance(value, (int, float)):
        value = value * 2
    return value

def json_setter(value):
    if isinstance(value, (int, float)):
        value = value / 2
    return value

class MyTable(Base):
    ...
    mutable_json = NestedMutableJSONProperty(
        "_mutable_json",
        fget=json_getter,
        fset=json_setter,
    )

Passed functions are executed in the existing getter and setter in the form of value = fc(value).