I am trying to use an autoincrementing unique ID field as a foreign key in other tables. My model is below:
class User(Base):
__tablename__ = 'Users'
uid = Column(INT, primary_key=True, autoincrement=True)
name = Column(TEXT)
email = Column(TEXT)
dateRegistered = Column(TIMESTAMP)
phone = Column(TEXT)
class AddressMap(Base):
__tablename__ = 'AddressMaps'
uid = Column(INT, primary_key=True, autoincrement=True)
userId = Column(INT, ForeignKey('Users.uid'))
addressId = Column(INT, ForeignKey('Addresses.uid'))
dateCreated = Column(TIMESTAMP)
user = relationship("User", backref=backref('AddressMaps'))
address = relationship("Address", backref=backref('AddressMaps'))
class Address(Base):
__tablename__ = 'Addresses'
uid = Column(INT, primary_key=True, autoincrement=True)
street = Column(TEXT)
city = Column(TEXT)
state = Column(TEXT)
postal = Column(TEXT)
dateRegistered = Column(TIMESTAMP)
My problem is that when I create a user object, it is not created with a uid value. I understand this is because the object has not yet been committed to the database. The problem is that since the User object has None as the uid value, I have no way of linking the AddressMap object with it.
What is the idiomatic way of handling this problem in SQLAlchemy?
You shouldn't need a uid. Since you have created a relationship between the tables, you will be able to add an AddressMap object to the user:
samantha = User(name='Sam', email='sam#xyz.abc', phone='555-555-5555')
You now have access to the samantha.AddressMaps collection (see your backref under your user relationship in your AddressMap table). You can add AddressMap objects to this collection:
samantha.AddressMaps = [AddressMap(dateCreated=datetime.now()),
AddressMap(dateCreated=datetime.min)]
Now you can add these objects to your session and commit. See the docs for more info.
Incidentally, just as an FYI, you don't need to include autoincrement=True on the first integer column of a table.
Related
I want to create a model for a mail service, each mail will have an author and a recipient, also each user must have sent and received messages
Here is my code
class User(Base, Find):
__tablename__ = "users"
id = Column(Integer, primary_key=True)
username = Column(String(30))
fullname = Column(String(50))
sent_mails = relationship("Mail", back_populates="author")
received_mails = relationship("Mail", back_populates="recipient")
def __repr__(self):
return f"User(id={self.id})"
class Mail(Base, Find):
__tablename__ = "mails"
id = Column(Integer, primary_key=True)
author_id = Column(Integer, ForeignKey("users.id"))
recipient_id = Column(Integer, ForeignKey("users.id"))
author = relationship("User", back_populates="sent_mails")
recipient = relationship("User", back_populates="received_mails")
def __repr__(self):
return f"Mail(id={self.id})"
When I try to use models I get an exception
sqlalchemy.exc.AmbiguousForeignKeysError: Could not determine join condition between parent/child tables on relationship User.sent_mails - there are multiple forei
gn key paths linking the tables. Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key refere
nce to the parent table.
What's my mistake?
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
I have follow model of my DB:
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
adr = relationship('Address', backref='uuu')
class Address(Base):
__tablename__ = 'addresses'
id = Column(Integer, primary_key=True)
email = Column(String, nullable=False)
# user_id = Column(Integer)
user_id = Column(Integer, ForeignKey('users.id'))
Base.metadata.create_all(engine)
answer = sess.query(User).first()
print(answer.adr)
It's print:
[<__main__.Address object at 0x7fed81592e50>]
But by the docs it should print value instead address.
The above configuration establishes a collection of Address objects on User called User.addresses. It also establishes a .user attribute on Address which will refer to the parent User object.
I tried follow code:
answer = sess.query(User).first()
print(answer.adr.email)
Error:
AttributeError: 'InstrumentedList' object has no attribute 'email'
What it prints is absolutely correct.
If you want values of individual columns, you need to print for example answer.adr.email. And note that answer.adr is a list, not an object, so you need to iterate through it as well.
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?
Hi im having some trouble with foreign key in sqlalchemy not auto incrementing on a primary key ID
Im using: python 2.7, pyramid 1.3 and sqlalchemy 0.7
Here is my models
class Page(Base):
__tablename__ = 'page'
id = Column(Integer, ForeignKey('mapper.object_id'), autoincrement=True, primary_key=True)
title = Column(String(30), unique=True)
title_slug = Column(String(75), unique=True)
text = Column(Text)
date_added = Column(DateTime)
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String(100), unique=True)
email = Column(String(100), unique=True)
password = Column(String(100))
class Group(Base):
__tablename__ = 'groups'
id = Column(Integer, primary_key=True)
name = Column(String(100), unique=True)
class Member(Base):
__tablename__ = 'members'
user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
group_id = Column(Integer, ForeignKey('groups.id'), primary_key=True)
class Resource(Base):
__tablename__ = 'resource'
id = Column(Integer, primary_key=True)
tablename = Column(Text)
action = Column(Text)
class Mapper(Base):
__tablename__ = 'mapper'
resource_id = Column(Integer, ForeignKey('resource.id'), primary_key=True)
group_id = Column(Integer, ForeignKey('groups.id'), primary_key=True)
object_id = Column(Integer, primary_key=True)
and here is my RAW SQL query which i've written in SQLAlchemys ORM
'''
SELECT g.name, r.action
FROM groups AS g
INNER JOIN resource AS r
ON m.resource_id = r.id
INNER JOIN page AS p
ON p.id = m.object_id
INNER JOIN mapper AS m
ON m.group_id = g.id
WHERE p.id = ? AND
r.tablename = ?;
'''
obj = Page
query = DBSession().query(Group.name, Resource.action)\
.join(Mapper)\
.join(obj)\
.join(Resource)\
.filter(obj.id == obj_id, Resource.tablename == obj.__tablename__).all()
the raw SQL Query works fine without any relations between Page and Mapper, but SQLAlchemys ORM seem to require a ForeignKey link to be able to join them. So i decided to put the ForeignKey at Page.id since Mapper.object_id will link to several different tables.
This makes the SQL ORM query with the joins work as expected but adding new data to the Page table results in a exception.
FlushError: Instance <Page at 0x3377c90> has a NULL identity key.
If this is an auto- generated value, check that the database
table allows generation of new primary key values, and that the mapped
Column object is configured to expect these generated values.
Ensure also that this flush() is not occurring at an inappropriate time,
such as within a load() event.
here is my view code:
try:
session = DBSession()
with transaction.manager:
page = Page(title, text)
session.add(page)
return HTTPFound(location=request.route_url('home'))
except Exception as e:
print e
pass
finally:
session.close()
I really don't know why, but i'd rather have the solution in SQLalchemy than doing the RAW SQL since im making this project for learning purposes :)
I do not think autoincrement=True and ForeignKey(...) play together well.
In any case, for join to work without any ForeignKey, you can just specify the join condition in the second parameter of the join(...):
obj = Page
query = DBSession().query(Group.name, Resource.action)\
.join(Mapper)\
.join(Resource)\
.join(obj, Resource.tablename == obj.__tablename__)\
.filter(obj.id == obj_id)\
.all()