SQLAlchemy: get Model from table name. This may imply appending some function to a metaclass constructor as far as I can see

So in SQLAlchemy version 1.4.x (which I updated to around 2020-03-16) it seems _decl_class_registry no longer exists.

I was able to work around using the new registry class attribute (which is not protected, so hopefully it wont be removed suddenly!).

Base.TBLNAME_TO_CLASS = {}

for mapper in Base.registry.mappers:
    cls = mapper.class_
    classname = cls.__name__
    if not classname.startswith('_'):
        tblname = cls.__tablename__
        Base.TBLNAME_TO_CLASS[tblname] = cls

Not sure if this is the best way to do it, but its how I did it.

For sqlalchemy 1.4.x (and probably 2.0.x for the future readers too) You can nicely extend the Erotemic answer to be more convenient when models are distributed across many files (such case is a primary reason for looking up ORM classes when doing proper OOP).

Take such class and make a Base from it:

from sqlalchemy.orm import declarative_base

class BaseModel:

    @classmethod
    def model_lookup_by_table_name(cls, table_name):
        registry_instance = getattr(cls, "registry")
        for mapper_ in registry_instance.mappers:
            model = mapper_.class_
            model_class_name = model.__tablename__
            if model_class_name == table_name:
                return model


Base = declarative_base(cls=BaseModel)

Then declaring your models, even in separate modules, enables You to use cls.model_lookup_by_table_name(...) method without importing anything, as long as You are deriving from a Base:

user_models.py

from sqlalchemy import Column, Integer

class User(Base):
    __tablename__ = "user"

    id = Column(Integer, primary_key=True)

    # ... and other columns

    def some_method(self):
        # successfully use lookup like this
        balance_model = self.model_lookup_by_table_name("balance")
        # ...
        return balance_model

balance_models.py

from sqlalchemy import Column, Integer

class Balance(Base):
    __tablename__ = "balance"

    id = Column(Integer, primary_key=True)

    # ... other columns

    def some_method(self):
        # lookup works on every model
        user_model = self.model_lookup_by_table_name("user")
        # ...
        return user_model

And it works as expected:

>>> User().some_method()
<class 'balance_models.Balance'>
>>> Balance().some_method()
<class 'user_models.User'>
>>> Base.model_lookup_by_table_name("user")
<class 'user_models.User'>
>>> Base.model_lookup_by_table_name("balance")
<class 'balance_models.Balance'>

You can safely cache the output of this method using functools.lru_cache to improve performance (avoiding python for loop when it is not needed). Also, You can add more lookups the same way, e.g. by a class name (not only by a table name like in this example)

if you are working with sqlalchemy automap, you need a slight modification. Took me couple minutes to tune it out:

def get_class_by_tablename(tablename, Base):
  for c in Base._decl_class_registry.values():
    if c.__table__.name == tablename:
      return c

One way would be to define a __table_cls__ classmethod in Base or as a mixin. Note that I haven't tested this with any sort of inheritance. An example if augmenting Base:

# Python 3.7.2, SQLAlchemy 1.3.13
###
# app/models.py
from sqlalchemy import Table
from sqlalchemy.ext.declarative import declarative_base

class Base(object):
    @classmethod
    def __table_cls__(cls, *args, **kwargs):
        t = Table(*args, **kwargs)
        t.decl_class = cls
        return t

Base = declarative_base(cls=Base)

Contriving a table example:

# app/models.py
class Account(Base):  # Note this is the customized Base class
    __tablename__ = 'account'
    id = Column(Integer, primary_key=True)
    name = Column(String, nullable=False)
    account_number = Column(String)

Testing in console:

# Python 3.7.2 Console
>>> from app import models as m
>>> account_table = m.Base.metadata.tables['account']
>>> account_table.__class__
<class 'sqlalchemy.sql.schema.Table'>

>>> account_table.decl_class
<class 'app.models.Account'>

As a function:

def get_class_by_table_name(table_name):
    tbl = Base.metadata.tables[table_name]
    return tbl.decl_class

Side note: since a lot of answers have referenced Base._decl_class_registry, the declarative_base() function also accepts a dictionary for the class_registry named parameter.

>>> registered_classes = {}
>>> Base = declarative_base(cls=Base, class_registry=registered_classes)
>>> registered_classes.keys()
dict_keys(['Account', '_sa_module_registry', 'AccountType', ...])

Old thread, but none of the answers here worked for me working with Flask-SQLAlchemy 2.5.1. and SQLAlchemy 1.4.32

As db.Model object you use in Flask-SQLAlchemy is practically identical to the Base model object in SQLAlchemy ORM, I think my answer below applies in the modern context.

This comment from @Supra621 seems to be the cleanest solution where you can simply do:

def get_class_from_tablename(tablename):
  for c in Base.__subclasses__():
    if c.__tablename__ == tablename:
      return c

Additionally, if you'd rather access this table object using the registry like the majority of the old answers here:

def get_class_from_tablename(tablename):
  for c in Base.registry._class_registry.data.values():
    if hasattr(c, '__tablename__') and c.__tablename__ == tablename:
      return c

Not sure from which version the attribute names change, but at least this works in both SQLAlchemy ORM and Flask SQLAlchemy (latest versions at the time of writing).