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Flask SQLAlchemy: adding third column to joining table

Context: I'm making an auctioning website for which I am using Flask-SQLAlchemy. My tables will need to have a many-to-many relationship (as one artpiece can have many user bids and a user can bid on many artpieces)
My question is: it is possible to add another column to my joining table to contain the id of the user bidding, the id of artpiece that they are bidding on and also how much they bid? Also if yes, how would I include this bid in the table when I add a record to said table?
bid_table = db.Table("bid_table",
db.Column("user_id", db.Integer, db.ForeignKey("user.user_id")),
db.Column("item_id", db.Integer, db.ForeignKey("artpiece.item_id"))
)
class User(db.Model):
user_id = db.Column(db.Integer, unique=True, primary_key=True, nullable=False)
username = db.Column(db.Integer, unique=True, nullable=False)
email = db.Column(db.String(50), unique =True, nullable=False)
password = db.Column(db.String(60), nullable=False)
creation_date = db.Column(db.DateTime, default=str(datetime.datetime.now()))
bids = db.relationship("Artpiece", secondary=bid_table, backref=db.backref("bids", lazy="dynamic"))
class Artpiece(db.Model):
item_id = db.Column(db.Integer, unique=True, primary_key=True, nullable=False)
artist = db.Column(db.String(40), nullable=False)
buyer = db.Column(db.String(40), nullable=False)
end_date = db.Column(db.String(40))
highest_bid = db.Column(db.String(40))

It is possible to do this with SQL Alchemy, but it's very cumbersome in my opinion.
SQLAlchemy uses a concept called an Association Proxy to turn a normal table into an association table. This table can have whatever data fields you want on it, but you have to manually tell SQLAlchemy which columns are foreign keys to the other two tables in question.
This is a good example from the documentation.
In your case, the UserKeyword table is the association proxy table that you want to build for your user/bid scenario.
The special_key column is the arbitrary data you would store like the bid amount.
from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.orm import backref, declarative_base, relationship
Base = declarative_base()
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String(64))
# association proxy of "user_keywords" collection
# to "keyword" attribute
keywords = association_proxy('user_keywords', 'keyword')
def __init__(self, name):
self.name = name
class UserKeyword(Base):
__tablename__ = 'user_keyword'
user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
keyword_id = Column(Integer, ForeignKey('keyword.id'), primary_key=True)
special_key = Column(String(50))
# bidirectional attribute/collection of "user"/"user_keywords"
user = relationship(User,
backref=backref("user_keywords",
cascade="all, delete-orphan")
)
# reference to the "Keyword" object
keyword = relationship("Keyword")
def __init__(self, keyword=None, user=None, special_key=None):
self.user = user
self.keyword = keyword
self.special_key = special_key
class Keyword(Base):
__tablename__ = 'keyword'
id = Column(Integer, primary_key=True)
keyword = Column('keyword', String(64))
def __init__(self, keyword):
self.keyword = keyword
def __repr__(self):
return 'Keyword(%s)' % repr(self.keyword)
Check out the full documentation for instructions on how to access and create this kind of model.
Having used this in a real project, it's not particularly fun and if you can avoid it, I would recommend it.
https://docs.sqlalchemy.org/en/14/orm/extensions/associationproxy.html

Flask SQLAlchemy: Child table with multiple parents?

I'm new to flask_sqlalchemy, and while I understand how the one-to-many, and many-to-many relationships work, I'm struggling to understand how I can apply them to my specific data types. I have the following three tables: TeamStat, PlayerStat, and Stat which are loosely described as follows
class PlayerStat(db.Model):
id = db.Column(db.Integer, primary_key=True)
date = db.Column(db.DateTime, nullable=False, default=datetime.datetime)
player_id = db.Column(db.Integer, db.ForeignKey('player.player_id'), nullable=False)
class TeamStat(db.Model):
id = db.Column(db.Integer, primary_key=True)
date = db.Column(db.DateTime, nullable=False, default=datetime.datetime)
team_id = db.Column(db.Integer, db.ForeignKey('team.team_id'), nullable=False)
class Stat(db.Model):
id = db.Column(db.Integer, primary_key=True)
value = db.Column(db.String(80), nullable=False)
Since Stat is a generic table type, I would like to use it by both the PlayerStat table (for individual player stats), as well as the TeamStat table (as a sum of the stats for all players on a team). Can someone help me understand how I can refer one child table to multiple parent tables in this fashion?

Use association tables to bridge your stat table to your players and team tables. This example is pretty close to what you are already doing, except the date column is moved on to the stat record table and I've replaced your PlayerStat and TeamStat objects with unmapped tables.
I've assumed you have two ORM classes, Player and Team (not Flask-SQLAlchemy sorry but concept remains the same):
plr_stat_assc = Table('plr_stat_assc', Base.metadata,
Column('player_id', Integer, ForeignKey('player.id')),
Column('stat_id', Integer, ForeignKey('stat.id'))
)
team_stat_assc = Table('team_stat_assc', Base.metadata,
Column('team_id', Integer, ForeignKey('team.id')),
Column('stat_id', Integer, ForeignKey('stat.id'))
)
class Player(Base):
__tablename__ = 'player'
id = Column(Integer, primary_key=True)
stats = relationship("Stat", secondary=plr_stat_assc)
class Team(Base):
__tablename__ = 'team'
id = Column(Integer, primary_key=True)
stats = relationship("Stat", secondary=team_stat_assc)
class Stat(Base):
__tablename__ = 'stat'
id = Column(Integer, primary_key=True)
date = Column(DateTime, nullable=False, default=datetime.datetime)
value = Column(String(80), nullable=False)

SQLAlchemy inserting data into two tables

I am just working on my first App based on SQLAlchemy and after couple hours of work with the documentation and some videos, I still can't fix the issue.
My app is a simple CRUD grocery list. I want to keep the category of the product in separate table so here comes relationship module of the SQLAlchemy. Error msg gives me no hint at all tbh.
engine = create_engine(my_database, echo = True)
connection = engine.connect()
Base = declarative_base()
session = sessionmaker(bind=engine)
class MyEnum(enum.Enum):
one = "pieces"
two = "kg"
class ProductTable(Base):
__tablename__ = 'product'
product_id = Column(Integer, primary_key=True)
product_name = Column(String(30), nullable=False)
product_quantity = Column(Integer, nullable=False)
product_type = Column(Enum(MyEnum), nullable=False)
category_id = Column(Integer, ForeignKey('category.id'), nullable=False)
category = relationship("category", back_populates="product")
product_description = Column(String(255))
class CategoryTable(Base):
__tablename__ = 'category'
id = Column(Integer, primary_key=True)
category_name = Column(String(25), nullable=False)
Base.metadata.create_all(engine)
session = session()
cc_product = ProductTable(product_id=1,
product_name="cucumber",
product_quantity="1",
product_type="kg",
product_description="For the salad")
cc_category= CategoryTable(category_name="vegetables")
session.add(cc_product, cc_category)
session.commit()
I. Creation of the tables finished smoothly with no errors, however, is the creation itself designed properly? Each product has single category but one category should be assigned to one or more product. I made that based on one to one relationship.
II. Inserting data to both tables. I want to insert data like:
Product_id = 1
Product_name = Cucumber
Product_quantity = 1
Product_type = "kg" or "pieces"
Category = Vegetables ( from the category table)
Description = "blah blah blah"
I think there is something wrong not only with the data inserting process but also with the tables creation.
Here is the error, which tbh, doesn't tell me anything:
sqlalchemy.exc.ArgumentError: relationship 'category' expects a class or a mapper argument (received: <class 'sqlalchemy.sql.schema.Table'>)

You have two mistakes:
you wrote "category" as the Mapper class instead of "CategoryTable"
forgot to create products on 'CategoryTable'
class ProductTable(Base):
__tablename__ = 'product'
product_id = Column(Integer, primary_key=True)
product_name = Column(String(30), nullable=False)
product_quantity = Column(Integer, nullable=False)
product_type = Column(Enum(MyEnum), nullable=False)
category_id = Column(Integer, ForeignKey('category.id'), nullable=False)
categories = relationship("CategoryTable", back_populates="products")
product_description = Column(String(255))
class CategoryTable(Base):
__tablename__ = 'category'
id = Column(Integer, primary_key=True)
category_name = Column(String(25), nullable=False)
products = relationship('ProductTable', back_populates='categories')
Some more changes are still needed:
change CategoryTable to Category (also for ProductTable, better names)
you'll have constraints failing after you'll get things running...

SQLAlchemy different tables for relationship?

Suppose I have the following tables/relationships defined:
class Post(Base):
__table_name__ = "post"
id = Column(Integer, primary_key=True)
text = Column(String(100))
class Comment(Base):
__table_name__ = "comment"
id = Column(Integer, primary_key=True)
post_id = Column(Integer, ForeignKey("post.id"), nullable=False)
text = Column(String(100))
Now, I want to have notifications of events, like "You were tagged in a comment" or "you were tagged in a post". Is there some way to have a foreign key relationship in SQLAlchemy that can point to either a comment or a post (or several other tables in reality)? Something like:
class Notification(Base):
__table_name__ = "notification"
id = Column(Integer, primary_key=True)
target = relationship(??either post or comment??)
user_id = Column(Integer, ForeignKey("users.id")
created_date = Column(Datetime, default=datetime.utcnow)
I suppose you could just put foreign keys to all the different types and make all but one null, but that seems ugly. I'd also rather not have multiple tables for each type of notification; as in comment_notification and post_notification. Any ideas?

SQLAlchemy Polymorphic Loading

I've this model in SQLAlchemy:
class User(Base):
__tablename = 'users'
id = Column(Integer, primary_key=True, autoincrement=True)
type = Column(Text, nullable=False)
user_name = Column(Text, unique=True, nullable=False)
__mapper_args__ = {'polymorphic_on': type}
class Client(User):
__tablename__ = 'clients'
__mapper_args__ = {'polymorphic_identity': 'client'}
id = Column(Integer, ForeignKey('users.id'), primary_key=True)
client_notes = Column(Text)
This is a joined table inheritance. The problem is when I'm querying User:
self.session.query(User).all()
all I get is records from clients, while what I want is all record on User without Client. How do I solve this problem?
Edit: I'm using SQLAlchemy 0.7.4 and Pyramid 1.3a3

session.query(User) does not perform any filtering based on the value of type column.
However, the SQL SELECT statement it generates selects only data from the users table (unless with_polymorphic(...) is used).
But you can add the filter explicitely to achive the desired result:
session.query(User).filter(User.type=='user').all()