model.py

import re

import sqlalchemy as sa
from sqlalchemy import inspect
from sqlalchemy.ext.declarative import DeclarativeMeta
from sqlalchemy.ext.declarative import declared_attr
from sqlalchemy.schema import _get_table_key


def should_set_tablename(cls):
    """Determine whether ``__tablename__`` should be automatically generated
    for a model.

    * If no class in the MRO sets a name, one should be generated.
    * If a declared attr is found, it should be used instead.
    * If a name is found, it should be used if the class is a mixin, otherwise
      one should be generated.
    * Abstract models should not have one generated.

    Later, :meth:`._BoundDeclarativeMeta.__table_cls__` will determine if the
    model looks like single or joined-table inheritance. If no primary key is
    found, the name will be unset.
    """
    if cls.__dict__.get("__abstract__", False) or not any(
        isinstance(b, DeclarativeMeta) for b in cls.__mro__[1:]
    ):
        return False

    for base in cls.__mro__:
        if "__tablename__" not in base.__dict__:
            continue

        if isinstance(base.__dict__["__tablename__"], declared_attr):
            return False

        return not (
            base is cls
            or base.__dict__.get("__abstract__", False)
            or not isinstance(base, DeclarativeMeta)
        )

    return True


def camel_to_snake_case(name):
    name = re.sub(r"((?<=[a-z0-9])[A-Z]|(?!^)[A-Z](?=[a-z]))", r"_\1", name)
    return name.lower().lstrip("_")


class NameMetaMixin(type):
    def __init__(cls, name, bases, d):
        if should_set_tablename(cls):
            cls.__tablename__ = camel_to_snake_case(cls.__name__)

        super().__init__(name, bases, d)

        # __table_cls__ has run at this point
        # if no table was created, use the parent table
        if (
            "__tablename__" not in cls.__dict__
            and "__table__" in cls.__dict__
            and cls.__dict__["__table__"] is None
        ):
            del cls.__table__

    def __table_cls__(cls, *args, **kwargs):
        """This is called by SQLAlchemy during mapper setup. It determines the
        final table object that the model will use.

        If no primary key is found, that indicates single-table inheritance,
        so no table will be created and ``__tablename__`` will be unset.
        """
        # check if a table with this name already exists
        # allows reflected tables to be applied to model by name
        key = _get_table_key(args[0], kwargs.get("schema"))

        if key in cls.metadata.tables:
            return sa.Table(*args, **kwargs)

        # if a primary key or constraint is found, create a table for
        # joined-table inheritance
        for arg in args:
            if (isinstance(arg, sa.Column) and arg.primary_key) or isinstance(
                arg, sa.PrimaryKeyConstraint
            ):
                return sa.Table(*args, **kwargs)

        # if no base classes define a table, return one
        # ensures the correct error shows up when missing a primary key
        for base in cls.__mro__[1:-1]:
            if "__table__" in base.__dict__:
                break
        else:
            return sa.Table(*args, **kwargs)

        # single-table inheritance, use the parent tablename
        if "__tablename__" in cls.__dict__:
            del cls.__tablename__


class BindMetaMixin(type):
    def __init__(cls, name, bases, d):
        bind_key = d.pop("__bind_key__", None) or getattr(cls, "__bind_key__", None)

        super().__init__(name, bases, d)

        if bind_key is not None and getattr(cls, "__table__", None) is not None:
            cls.__table__.info["bind_key"] = bind_key


class DefaultMeta(NameMetaMixin, BindMetaMixin, DeclarativeMeta):
    pass


class Model:
    """Base class for SQLAlchemy declarative base model.

    To define models, subclass :attr:`db.Model <SQLAlchemy.Model>`, not this
    class. To customize ``db.Model``, subclass this and pass it as
    ``model_class`` to :class:`SQLAlchemy`.
    """

    #: Query class used by :attr:`query`. Defaults to
    # :class:`SQLAlchemy.Query`, which defaults to :class:`BaseQuery`.
    query_class = None

    #: Convenience property to query the database for instances of this model
    # using the current session. Equivalent to ``db.session.query(Model)``
    # unless :attr:`query_class` has been changed.
    query = None

    def __repr__(self):
        identity = inspect(self).identity

        if identity is None:
            pk = f"(transient {id(self)})"
        else:
            pk = ", ".join(str(value) for value in identity)

        return f"<{type(self).__name__} {pk}>"