Support for Flask-SQLAlchemy models that have `__init__` arguments

[razzius]

Consider the todo example from Flask-SQLAlchemy:

from datetime import datetime
from flask import Flask
from flask_sqlalchemy import SQLAlchemy
from mixer.backend.sqlalchemy import mixer

app = Flask(__name__)
db = SQLAlchemy(app)

class Todo(db.Model):
    __tablename__ = 'todos'
    id = db.Column('todo_id', db.Integer, primary_key=True)
    title = db.Column(db.String(60))
    text = db.Column(db.String)
    pub_date = db.Column(db.DateTime)

    def __init__(self, title, text):
        self.title = title
        self.text = text
        self.pub_date = datetime.utcnow()

If we try to use mixer with it:

mixer.blend(Todo)

---------------------------------------------------------------------------
TypeError                                 Traceback (most recent call last)
<ipython-input-1-8a1d24676132> in <module>()
     19         self.pub_date = datetime.utcnow()
     20
---> 21 mixer.blend(Todo)

/Users/razzi/local/venvs/thornm/lib/python2.7/site-packages/mixer/main.pyc in blend(self, scheme, **values)
    596         type_mixer = self.get_typemixer(scheme)
    597         try:
--> 598             return type_mixer.blend(**values)
    599         except Exception:
    600             if self.params.get('silence'):

/Users/razzi/local/venvs/thornm/lib/python2.7/site-packages/mixer/main.pyc in blend(self, **values)
    145                 values.append((name, value))
    146
--> 147         target = self.populate_target(values)
    148
    149         # Run registered middlewares

/Users/razzi/local/venvs/thornm/lib/python2.7/site-packages/mixer/main.pyc in populate_target(self, values)
    168     def populate_target(self, values):
    169         """ Populate target with values. """
--> 170         target = self.__scheme()
    171         for name, value in values:
    172             setattr(target, name, value)

TypeError: __init__() takes exactly 3 arguments (1 given)

mixer attempts to __init__ without any arguments, which throws an error. Would supporting a model defined this way be feasible/desirable?

One way to get around this is to make all fields have defaults in the __init__:

class User(Base):
    __tablename__ = 'users'
    id = Column(Integer, primary_key=True)
    name = Column(String(50), unique=True)
    email = Column(String(120), unique=True)

    def __init__(self, name=None, email=None):
        self.name = name
        self.email = email

At the very least, putting a note in the docs that models with required __init__ parameters are unsupported might save others some confusion.

[klen]

I little bit dont understand what the reason for redefine __init__ method of SQLAlchemy models. But as one of solution you can easy create own mixer:

from mixer.backend.sqlalchemy import Mixer

class MyOwnMixer(Mixer):
    def populate_target(self, values):
        target = self.__scheme(**values)
        return target

mixer = MyOwnMixer()

[klen]

Maybe I will add this behavior as param to sqlalchemy mixer.

[razzius]

I do agree that using the default __init__ makes more sense — models with more than a couple fields are best constructed using named arguments rather than enforcing an arbitrary order.

Perhaps the Flask examples could be updated recommending this approach, if others feel the same way.

[klen]

Updated README and docs.

[anthon-alindada]

Hi, Is this fix still working. I've tried creating my own mixer but it does not work. I tried to put a logger inside the populate_target and its not triggering the log. I'm not sure with this but i think its not overriding the populate_target. I'm not even sure if i'm doing it right. Can someone help me with this.

Here's the error

Traceback (most recent call last): File "/usr/local/lib/python3.5/dist-packages/mixer/main.py", line 568, in blend return type_mixer.blend(**values) File "/usr/local/lib/python3.5/dist-packages/mixer/main.py", line 134, in blend target = self.populate_target(values) File "/usr/local/lib/python3.5/dist-packages/mixer/backend/sqlalchemy.py", line 254, in populate_target target = self.__scheme() TypeError: Mixer (<class 'app.users.models.User'>): __init__() missing 3 required positional arguments: 'email', 'first_name', and 'last_name'

[smoll]

I ran into the same issue as @anthon-alindada - it looks like the code changed since the example in the README was created. This worked for me:

class CustomTypeMixer(TypeMixer):
    def __init__(self, cls, mixer=None, factory=None, fake=True):
        super().__init__(cls, mixer=mixer, factory=factory, fake=fake)
        self.__scheme = cls  # not sure why above line isn't setting this... is this the keyword 'cls' or just a variable named 'cls'?

    def populate_target(self, values):
        """ Populate a target by values. """
        target = self.__scheme(**dict(values))
        return target

class CustomMixer(Mixer):
    type_mixer_cls = CustomTypeMixer

mixer = CustomMixer(session=session, commit=True)
organization = mixer.blend(Organization, internal_name='foo', name='Foo')