Context
I have a simple MySQL database written with SQLAlchemy. The following are my two models, Subreddit and Keyword, that have a many-to-many relationship, along with their association table:
subreddits_keywords = db.Table('subreddits_keywords', db.Model.metadata,
db.Column('subreddit_id', db.Integer, db.ForeignKey('subreddits.id', ondelete='CASCADE')),
db.Column('keyword_id', db.Integer, db.ForeignKey('keywords.id', ondelete='CASCADE')),
)
class Subreddit(db.Model, JsonSerializer):
__tablename__ = 'subreddits'
id = db.Column(db.Integer, primary_key=True)
subreddit_name = db.Column(db.String(128), index=True)
# Establish a parent-children relationship (subreddit -> keywords).
keywords = db.relationship('Keyword', secondary=subreddits_keywords, backref='subreddits', cascade='all, delete', passive_deletes=True, lazy='dynamic')
// ...
class Keyword(db.Model, JsonSerializer):
__tablename__ = 'keywords'
id = db.Column(db.Integer, primary_key=True)
keyword = db.Column(db.String(128), index=True)
// ...
As test data, I've created the following data set:
Subreddit:
test_subreddit
Keywords:
test_keyword1
test_keyword2
test_keyword3
In other words, test_subreddit.keywords should return [test_keyword1, test_keyword2, test_keyword3].
Problem
When I remove test_subreddit, test_keyword1, test_keyword2, test_keyword3 still persist in the database.
I understand that with many-to-many relationships, there is technically no parent so cascade's technically will not work according to this post:
https://stackoverflow.com/a/803584/10426919.
What I've Tried
I followed this link: https://github.com/sqlalchemy/sqlalchemy/wiki/ManyToManyOrphan.
This link provides a library function that should fix my exact problem.
However, the function does not work when integrated into my Model file in the following ways:
Method #1:
from app.extensions import db
from werkzeug.security import generate_password_hash, check_password_hash
from sqlalchemy.inspection import inspect
from sqlalchemy_utils import auto_delete_orphans <------ # library
subreddits_keywords = db.Table('subreddits_keywords', db.Model.metadata,
db.Column('subreddit_id', db.Integer, db.ForeignKey('subreddits.id', ondelete='CASCADE')),
db.Column('keyword_id', db.Integer, db.ForeignKey('keywords.id', ondelete='CASCADE')),
)
class Subreddit(db.Model, JsonSerializer):
__tablename__ = 'subreddits'
id = db.Column(db.Integer, primary_key=True)
subreddit_name = db.Column(db.String(128), index=True)
# Establish a parent-children relationship (subreddit -> keywords).
keywords = db.relationship('Keyword', secondary=subreddits_keywords, backref='subreddits', cascade='all, delete', passive_deletes=True, lazy='dynamic')
// ...
class Keyword(db.Model, JsonSerializer):
__tablename__ = 'keywords'
id = db.Column(db.Integer, primary_key=True)
keyword = db.Column(db.String(128), index=True)
// ...
auto_delete_orphans(Subreddit.keywords) <------ # Library function
However, this function does not seem to do anything. There is no error that is output to help guide me towards the right direction. When I check my database in MySQL workbench, the Subreddit, test_subreddit, is deleted, but the keywords [test_keyword1, test_keyword2, test_keyword3] are still in the database under the Keywords table.
Method #2:
I tried integrating the actual function, that the library function is based on, into my code as well:
from app.extensions import db
from werkzeug.security import generate_password_hash, check_password_hash
from sqlalchemy.inspection import inspect
from sqlalchemy_utils import auto_delete_orphans
# for deleting many-to-many "orphans".
from sqlalchemy import event, create_engine
from sqlalchemy.orm import attributes, sessionmaker
subreddits_keywords = db.Table('subreddits_keywords', db.Model.metadata,
db.Column('subreddit_id', db.Integer, db.ForeignKey('subreddits.id', ondelete='CASCADE')),
db.Column('keyword_id', db.Integer, db.ForeignKey('keywords.id', ondelete='CASCADE')),
)
class Subreddit(db.Model, JsonSerializer):
__tablename__ = 'subreddits'
id = db.Column(db.Integer, primary_key=True)
subreddit_name = db.Column(db.String(128), index=True)
# Establish a parent-children relationship (subreddit -> keywords).
keywords = db.relationship('Keyword', secondary=subreddits_keywords, backref='subreddits', cascade='all, delete', passive_deletes=True, lazy='dynamic')
// ...
class Keyword(db.Model, JsonSerializer):
__tablename__ = 'keywords'
id = db.Column(db.Integer, primary_key=True)
keyword = db.Column(db.String(128), index=True)
// ...
engine = create_engine("mysql://", echo=True)
Session = sessionmaker(bind=engine)
#event.listens_for(Session, 'after_flush')
def delete_tag_orphans(session, ctx):
# optional: look through Session state to see if we want
# to emit a DELETE for orphan Tags
flag = False
for instance in session.dirty:
if isinstance(instance, Subreddit) and \
attributes.get_history(instance, 'keywords').deleted:
flag = True
break
for instance in session.deleted:
if isinstance(instance, Subreddit):
flag = True
break
# emit a DELETE for all orphan Tags. This is safe to emit
# regardless of "flag", if a less verbose approach is
# desired.
if flag:
session.query(Keyword).\
filter(~Keyword.subreddits.any()).\
delete(synchronize_session=False)
Again, the keywords persisted despite being attached to no parent.
What I'm trying to accomplish
When children in the database no longer have a parent, I would like them to be removed from the database. What am I doing wrong?
Rather than using auto_delete_orphans, I created a method that I can call when I want to delete children. This method checks the child in question, and sees if it has any parents. If it does have a parent, we leave it be, but if it does not have a parent, we then delete the children.
Here is how I implemented this method, given that a Subreddit is a parent and a Keyword is a child of Subreddit.
def check_for_keyword_orphans(keyword):
# check if each keyword has an associated subreddit
if len(keyword.subreddits) == 0:
db.session.delete(keyword)
return True # keyword deleted
else:
return False # keyword has an associated subreddit
And here is how I used the method in my API route:
keywords = subreddit.keywords
for keyword in keywords:
check_for_keyword_orphans(keyword)
db.session.commit()
I have a model which has several ForeignKeys:
class Employee(models.Model):
company = models.ForeignKey(Company, on_delete=models.CASCADE, related_name="staff", null=False, blank=False)
user = models.ForeignKey(to=User, blank=False, null=False, on_delete=models.CASCADE)
roles = models.ManyToManyField(to=Role, blank=False)
How do I use a fields from Company and User in Employee model? I need them for __str__.
you can access these as attributes of the self.company or self.user, since self.company will return a Company object.
You thus can work with:
class Employee(models.Model):
company = models.ForeignKey(
Company,
on_delete=models.CASCADE,
related_name='staff'
)
user = models.ForeignKey(
User,
on_delete=models.CASCADE
)
roles = models.ManyToManyField(Role)
def __str__(self):
return f'{self.company} {self.user.username}'
Note: It is normally better to make use of the settings.AUTH_USER_MODEL [Django-doc] to refer to the user model, than to use the User model [Django-doc] directly. For more information you can see the referencing the User model section of the documentation.
I am using DRF for creating API, using basic APIView. Below are the models and views.
models.py
from django.db import models
from django.utils import timezone
class PizzaOrder(models.Model):
name = models.CharField(max_length=120)
size = models.CharField(default='MEDIUM')
customer_name = models.CharField(max_length=120)
customer_address = models.TextField()
ordered_time = models.DateTimeField(default=timezone.now)
Now, I need two things in that.
First - I want to set STATUS as 'open' in the database while ordering pizza. User isn't able to see the STATUS column while saving.
Second - I want to get all orders, but it should show STATUS to the user now.
view.py
class PizzaOrderView(APIView):
def get(self, request):
orders = PizzaOrder.objects.all()
serializer = ArticleSerializer(orders, many=True)
return Response({"orders": serializer.data})
def post(self, request):
orders = request.data.get('orders')
serializer = ArticleSerializer(data=orders)
if serializer.is_valid(raise_exception=True):
article_saved = serializer.save()
What should I do to get my all two requirements?
First of all if you want to save status in the database you must include it as one of the fields in your model. I would also suggest adding the choices enumeration so that nothing unwanted can end up in database as a status (note that you can add any other choice besides open and closed):
class PizzaOrder(models.Model):
...
OPEN = 'open'
CLOSED = 'closed'
TYPE_CHOICES = (
(OPEN, 'Open'),
(CLOSED, 'Closed'),
)
status = models.CharField(max_length=120, choices=STATUS_CHOICES, default=OPEN)
Next thing to know is that the way data is presented to the user depends mostly on your serializers (would be useful if you could include those in your question aswell). So for serializing the PizzaOrder data you can use two different serializers (one which includes the status field, and one which does not):
class PizzaOrderSerializer(serializers.ModelSerializer):
class Meta:
model = PizzaOrder
fields = '__all__'
class PizzaOrderWithoutStatusSerializer(serializers.ModelSerializer):
class Meta:
model = PizzaOrder
fields = ['name', 'size', 'customer_name', 'customer_address', 'ordered_time']
you can user one serializer just just using the one serializer
class PizzaOrderSerializer(serializers.ModelSerializer):
class Meta:
model = PizzaOrder
fields = '__all__'
read_only_fields = ('status',)
I have a User model, and a Playlist model, which references user_id as a foreign key
models.py
class User(db.Model):
__tablename__ = 'users'
id = db.Column(db.Integer, primary_key=True, autoincrement=True)
playlists = db.relationship("Playlist",
backref=db.backref('user'),
uselist=True)
def serialize(self):
"""Return object data in easily serializeable format"""
return {
'id': self.id,
'playlists' : self.playlists}
class Playlist(db.Model):
"""
Model for storing playlist information belonging to a specific user
"""
__tablename__ = 'playlist'
id = db.Column(db.Integer, primary_key=True)
title = db.Column(db.String(50))
user_id = db.Column(db.Integer, db.ForeignKey('users.id'))
#property
def serialize(self):
"""Return object data in easily serializeable format"""
return {
'id' : self.id,
'created' : self.created,
'title': self.title,
}
methods.py
def Upload_Tracks(dataset):
try:
playlist = Playlist.query.filter(Playlist.title == 'Cache').first()
if not playlist:
# create one
playlist = Playlist(title='Cache',
user=User.query.get(1))
db.session.add(playlist)
db.session.commit()
db.session.commit()
else:
playlist = Playlist.query.filter(
and_(Playlist.title == 'Cache', User.id == 1)).first()
# handler errors
except (exc.IntegrityError, ValueError):
db.session.rollback()
return {"status": True}
At first iteration of, playlist is created ADDED NEW <Playlist 'Cache'>, but at second iteration, when code reaches else, I'm getting AttributeError: 'NoneType' object for playlist here:
playlist = Playlist.query.filter(
and_(Playlist.title == 'Cache', User.id == 1)).first()
If I query filtering only one attribute, like so:
playlist = Playlist.query.filter(
(Playlist.title == 'Cache')).first()
it works.
So how do I query playlist by title AND user_id at the same time?
You get the above error because you tried to call User.id attribute but you didn't join that model (table) with Playlist model (table).
SQL has JOINs to join two tables (LEFT, RIGHT, INNERJOIN ...).
SQLAlchemy which you use handle this raw SQL by using join method.
So you have to use join() method to join two tables (models).
playlist = Playlist.query.join(User, User.id == Playlist.user_id).filter(
and_(Playlist.title == 'Cache', User.id == 1)).first()
You will get playlist as None (if there is no row like this in db) or Object if there is row like this.
I am building a app using flask-appbuilder and I have an action that runs a function and I want to update the row in the table with the output of function. Can't work out how to do it. Any help? Thanks
#action("prospect", "Prospect", "off we go", "fa-rocket")
def prospect(self, items):
if isinstance(items, list):
for a in items:
out = self.myfunction(a.name)
#Need to update the table with output
#anyideas?
self.update_redirect()
else:
print "nothing"
return redirect(self.get_redirect())
I'm assuming this is a View that is related to a model. If this is the case, you relate the model to the view using Flask-AppBuilder SQLAInterface class.
This class allows you to interact with the item in the database.
This class has an 'edit' method that let's you update the item.
Let's say your model is like the one below:
class Contact(Model):
id = Column(Integer, primary_key=True)
name = Column(String(50), unique = True, nullable=False)
Let's say you want to implement an action that capiltalizes the contact name, and you want to be able to do it on the the 'List' and 'Show' views. This is one way to do it:
class ContactView(ModelView):
datamodel = SQLAInterface(Contact)
#action("capitalize",
"Capitalize name",
"Do you really want to capitalize the name?")
def capitalize(self, contacts):
if isinstance(contacts, list):
for contact in contacts:
contact.name = contact.name.capitalize()
self.datamodel.edit(contact)
self.update_redirect()
else:
contacts.name = contacts.name.capitalize()
self.datamodel.edit(contacts)
return redirect(self.get_redirect())
You can check other SQLAInterface methods here.