I have two tables, users and contacts. I query the contacts table and get a list of a user's contacts. I would then like to be able to write Contact.first_name (where first_name is a row from the users table) and print out that contact's first name.
Currently, my Contact object does not recognize any attributes of the user table.
Here is some code:
class User(Base):
""" Basic User definition """
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
first_name = Column(Unicode(255))
last_name = Column(Unicode(255))
contacts = relationship('Contact', backref='users')
class Contact(Base):
__tablename__ = 'contacts'
id = Column(Integer, primary_key=True)
user_id = Column(Integer)
contact_id = Column(Integer)
__table_args__ = (ForeignKeyConstraint([id], [User.id]), {})
Here is my query:
Contact.query.filter(Contact.user_id == self.user_id).filter(Contact.state == True).all()
To be honest, I'm unsure of how to properly map my two foreign keys Contact.user_id and Contact.contact_id to the User.id row. Maybe this is the source of my problem?
I'm very new to using SQLAlchemy, so this is a learning experience here. Thanks for your help.
What you have here is class User which essentially refers to itself. In other words, it's a self-referential many-to-many relationship. Your model definitions should look like this:
# This is so called association table, which links two tables in many-to-many
# relationship. In this case it links same table's ('users') different rows.
user_contacts = Table(
'user_contacts', Base.metadata,
Column('user_id', Integer, ForeignKey('users.id'), primary_key=True),
Column('contact_id', Integer, ForeignKey('users.id'), primary_key=True),
)
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
first_name = Column(String)
last_name = Column(String)
contacts = relationship(
'User',
secondary=user_contacts,
primaryjoin=id==user_contacts.c.user_id,
secondaryjoin=id==user_contacts.c.contact_id
)
Then you can do things like the following:
u1 = User(first_name='Foo', last_name='Foo')
u2 = User(first_name='Bar', last_name='Bar')
u3 = User(first_name='Baz', last_name='Baz')
u1.contacts = [u2, u3]
session.add(u1)
session.commit()
# ... and in some other place in your code ...
u = User.query.get(1)
print u.contacts[0].first_name
Related
My models look like this:
class Company(DB_BASE):
__tablename__ = 'Company'
id = Column(Integer, primary_key=True, index=True)
...
products = relationship('Product', secondary=Company_Products, backref='Company')
class Product(DB_BASE):
__tablename__ = 'Product'
id = Column(Integer, primary_key=True, index=True)
...
companies = relationship('Company', secondary=Company_Products, backref='Product')
This is my association table
Company_Products = Table(
'Company_Products',
DB_BASE.metadata,
Column('id', Integer, primary_key=True),
Column('company_id', Integer, ForeignKey('Company.id')),
Column('product_id', Integer, ForeignKey('Product.id')),
Column('quantity', Integer, default=0),
Column('price_per_unit', Integer, default=0),
)
And this is how I'm querying the association table.
company_product = db.query(Company_Products).filter_by(product_id=id, company_id=user.company_id).first()
company_product.quantity = data.data['quantity']
company_product.price = data.data['price']
After creating the many-to-many relationship between a Company and a Product, I would like to modify the relationship extra data, quantity and price_per_unit in this instance. After querying the association object, modifying any attribute yields:
AttributeError: can't set attribute 'quantity'
Follow up on my question, the solution which ended up working for me is making a new model and using it to somewhat simulate an association table.
class Company_Products(DB_BASE):
__tablename__ = 'Company_Products'
id = Column(Integer, primary_key=True, index=True)
...
quantity = Column(String) # 1 - client, 2 - furnizor
price_per_unit = Column(String)
company_id = Column(Integer, ForeignKey('Company.id'))
company = relationship('Company', back_populates='products', lazy='select')
product_id = Column(Integer, ForeignKey('Product.id'))
product = relationship('Product', back_populates='companies', lazy='select')
This is definitely not the best solution, if I come up with something else or come across something which might work out, I will edit this.
I've three tables User, Device and Role. I have created a many-to-many relation b/w User and Device like this;
#Many-to-Many relation between User and Devices
userDevices = db.Table("user_devices",
db.Column("id", db.Integer, primary_key=True),
db.Column("user_id", db.Integer, db.ForeignKey("user.id")),
db.Column("device_id", db.Integer, db.ForeignKey("device.id"))))
class User(db.Model):
__tablename__ = 'user'
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(60), index=True, unique=True)
devices = db.relationship("Device", secondary=userDevices, backref=db.backref('users'), lazy="dynamic")
class Device(db.Model):
__tablename__ = 'device'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(60), unique=True)
This works quiet well. I can assign a device d1 to user u1 > d1.users.append(u1), and user to device > u1.devices.append(d1) and db.session.commit().
What I want more is to extend the table user_devices with one more column as role_id which will be ForeignKey for Role table. So that this table user_devices will clearly describe a Role for specific User on specific Device. after adding a column role_id in table user_devices I described Role table as;
class Role(db.Model):
__tablename__ = 'role'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(60), unique=True)
device = db.relationship("Device", secondary=userDevices, backref=db.backref('roles'), lazy="dynamic")
In this way, how can I assign a Role r1 to User u1 on Device d1 ?
here is what I tried:
# First get the device, user and role
deviceRow = db.session.query(Device).filter(Device.name=="d1").first()
userRow = db.session.query(User).filter(User.username=="u1").first()
roleRow = db.session.query(Role).filter(Role.name == "r1").first()
# Then add the user on that device
deviceRow.users.append(userRow)
deviceRow.roles.append(roleRow)
This creates two rows in the table user_devices
Is there any way that we could add two attributes into the table like this ?;
deviceRow.users.append(userRow).roles.append(roleRow)
so that it creates only one row after commit() ?
An association of 3 entities is no more a simple many to many relationship. What you need is the association object pattern. In order to make handling the association a bit easier map it as a model class instead of a simple Table:
class UserDevice(db.Model):
__tablename__ = "user_devices"
id = db.Column(db.Integer, primary_key=True)
user_id = db.Column(db.Integer, db.ForeignKey("user.id"), nullable=False)
device_id = db.Column(db.Integer, db.ForeignKey("device.id"), nullable=False)
role_id = db.Column(db.Integer, db.ForeignKey("role.id"), nullable=False)
__table_args__ = (db.UniqueConstraint(user_id, device_id, role_id),)
user = db.relationship("User", back_populates="user_devices")
device = db.relationship("Device")
role = db.relationship("Role", back_populates="user_devices")
class User(db.Model):
__tablename__ = "user"
id = db.Column(db.Integer, primary_key=True)
username = db.Column(db.String(60), index=True, unique=True)
user_devices = db.relationship("UserDevice", back_populates="user")
class Role(db.Model):
__tablename__ = "role"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(60), unique=True)
user_devices = db.relationship("UserDevice", back_populates="role")
To associate a user with a device and a role create a new UserDevice object:
device = db.session.query(Device).filter(Device.name == "d1").first()
user = db.session.query(User).filter(User.username == "u1").first()
role = db.session.query(Role).filter(Role.name == "r1").first()
assoc = UserDevice(user=user, device=device, role=role)
db.session.add(assoc)
db.session.commit()
Note that the ORM relationships are no longer simple collections of Device etc., but UserDevice objects. This is a good thing: when you iterate over user.user_devices for example, you get information on both the device and the role the user has on it. If you do wish to provide the simpler collections as well for situations where you for example don't need the role information, you can use an associationproxy.
There is a way to have 3-way many-to-many that is not a composition of two many-to-many relationships. You need an association object because the syntax for using just a Table doesn't allow 3-way many-to-many (because secondary explicitly refers to a 2-way many-to-many).
Here is a minimum example of how to do that in general:
from sqlalchemy import ForeignKey, Column, Integer, String
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base, declared_attr
Base = declarative_base()
# Helper classes to simplify the other classes:
# 1. Adds ch column
# 2. Defines how to print it
class Ch:
ch = Column(String, nullable=False)
def __str__(self):
return self.ch
# 3. Automatically determines table name (for foreign key)
class AutoNamed:
#declared_attr
def __tablename__(cls):
return cls.__name__
class ABC(AutoNamed, Base):
a_id = Column(Integer, ForeignKey('A.a_id'), primary_key=True)
b_id = Column(Integer, ForeignKey('B.b_id'), primary_key=True)
c_id = Column(Integer, ForeignKey('C.c_id'), primary_key=True)
a = relationship('A', back_populates='abcs')
b = relationship('B', back_populates='abcs')
c = relationship('C', back_populates='abcs')
def __repr__(self):
return f'{self.a} {self.b} {self.c}'
class A(Ch, AutoNamed, Base):
a_id = Column(Integer, primary_key=True)
abcs = relationship('ABC', back_populates='a')
class B(Ch, AutoNamed, Base):
b_id = Column(Integer, primary_key=True)
abcs = relationship('ABC', back_populates='b')
class C(Ch, AutoNamed, Base):
c_id = Column(Integer, primary_key=True)
abcs = relationship('ABC', back_populates='c')
Ok, now a little explanation:
ABC is an association table that needs a single instance of each of the tables in the 3-way many-to-many.
Each of A, B, C will have references to all ABC objects that involve them added automatically when you instantiate an ABC instance.
There is a gotchya: when you use relationship.secondary, the property on the object is a list of the other type (in their case, parent.children is a list of Children objects). However, in the docs for "association objects", when translating this to Association objects, although they still name the property on the parent object children, it is actually a list of Association objects. Here, I make this explicit by calling the property abcs.
You can instantiate these like normal:
anA = A(ch='x')
anB = B(ch='y')
anC = C(ch='z')
anABC = ABC(a=anA, b=anB, c=anC)
sess.add(anABC)
As a sanity check, here's the SQL that gets generated from this for SQLite. Exactly what we expect.
CREATE TABLE "A" (
ch VARCHAR NOT NULL,
a_id INTEGER NOT NULL,
PRIMARY KEY (a_id)
);
CREATE TABLE "B" (
ch VARCHAR NOT NULL,
b_id INTEGER NOT NULL,
PRIMARY KEY (b_id)
);
CREATE TABLE "C" (
ch VARCHAR NOT NULL,
c_id INTEGER NOT NULL,
PRIMARY KEY (c_id)
);
CREATE TABLE "ABC" (
a_id INTEGER NOT NULL,
b_id INTEGER NOT NULL,
c_id INTEGER NOT NULL,
PRIMARY KEY (a_id, b_id, c_id),
FOREIGN KEY(a_id) REFERENCES "A" (a_id),
FOREIGN KEY(b_id) REFERENCES "B" (b_id),
FOREIGN KEY(c_id) REFERENCES "C" (c_id)
);
Still wrapping my head around SqlAlchemy and have run into a few issues. Not sure if it is because I am creating the relationships incorrectly, querying incorrect, or both.
The general idea is...
one-to-many from location to user (a location can have many users but users can only have one location).
many-to-many between group and user (a user can be a member of many groups and a group can have many members).
Same as #2 above for desc and user.
My tables are created as follows:
Base = declarative_base()
class Location(Base):
__tablename__ = 'location'
id = Column(Integer, primary_key=True)
name = Column(String)
group_user_association_table = Table('group_user_association_table', Base.metadata,
Column('group_id', Integer, ForeignKey('group.id')),
Column('user_id', Integer, ForeignKey('user.id')))
class Group(Base):
__tablename__ = 'group'
id = Column(Integer, primary_key=True)
name = Column(String)
users = relationship('User', secondary=group_user_association_table, backref='group')
desc_user_association_table = Table('desc_user_association', Base.metadata,
Column('desc_id', Integer, ForeignKey('desc.id')),
Column('user_id', Integer, ForeignKey('user.id')))
class Desc(Base):
__tablename__ = 'desc'
id = Column(Integer, primary_key=True)
name = Column(String)
users = relationship('User', secondary=desc_user_association_table, backref='desc')
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
user_name = Column(String)
location_id = Column(Integer, ForeignKey('location.id'))
groups = Column(String, ForeignKey('group.id'))
descs = Column(String, ForeignKey('desc.id'))
location = relationship('Location', backref='user')
Here are some examples as to how I am creating the data (all being scraped from the web):
location = Location(id=city[1], name=city[0]) #city = ('name', id)
profile = User()
profile.id = int(str(span2class[0].a['href'][7:]))
profile.user_name = str(span2class[0].a.img['alt'])
profile.location_id = location.id
g = Group(id=gid, name=str(group.contents[0])) # add the group to the Group table
self.db_session.add(g)
# Now add the gid to a list that will be added to the profile that eventually gets added to the user table
profile.groups.append(str(gid)) # stick the gid into the list
profile.groups = ','.join(profile.groups) # convert list to csv string
# Repeat basically same thing above for desc
self.db_session.add(profile)
self.db_session.commit()
As far as queries go, I've got some of the basic ones working such as:
for instance in db_session.query(User).all():
print instance.id, instance.user_name
But when it comes to performing a join to get (for example) group.id and group.name for a specific user.id... nothing I've tried has worked. I am guessing that the form would be something like the following:
db_session.query(User, Group).join('users').filter(User.id==42)
but that didn't work.
Joins works from left to right, so you should join on the relationship from User to Group:
db_session.query(User, Group).join(User.group).filter(User.id == 42)
But this return you a list of tuples (<User>, <Group>), so if the user belongs to 2 or more groups, you will receive 2 or more rows.
If you really want to load both the user and its groups in one (SQL) query, a better way would be to load a user, but configure query to preload groups:
u = (session.query(User)
.options(joinedload(User.group))
.get(42)
)
print("User = {}".format(u))
for g in u.group:
print(" Group = {}".format(g))
I created a many to many relationship with sqlalchemy like this:
subject_books = Table('subject_books', Base.metadata,
Column('subject_id', Integer, ForeignKey('subjects.id')),
Column('book_id', Integer, ForeignKey('books.id')),
Column('group', Integer)
)
class Subject(Base):
__tablename__ = 'subjects'
id = Column(Integer, primary_key=True)
value = Column(Unicode(255), unique=True)
class Book(Base):
__tablename__ = 'books'
id = Column(Integer, primary_key=True)
title = Column(Unicode(255))
isbn = Column(Unicode(24))
subjects = relationship('Subject', secondary=subject_books, collection_class=attribute_mapped_collection('group'), backref='books')
after that I created a test like following:
book = Book(title='first book',isbn='test')
book.subjects[0] = Subject(value='first subject')
book.subjects[1] = Subject(value='second subject')
session.add(book)
transaction.commit()
and it works fine. But what I really want is to store more than one subject with the same group value, so I tried the following test:
book = Book(title='first book',isbn='test')
book.subjects[0] = [Subject(value='first subject'),Subject(value='second subject')]
book.subjects[1] = [Subject(value='third subject'),Subject(value='forth subject')]
session.add(book)
transaction.commit()
but it does not work.
Can this be done using sqlalchemy?
Thanks in Advance
Razi
I think you are constructing wrong relation ship.
Your relation ship must be
book M2M subject
subject M2M group
So you have to create one more model for group and that must be assign as m2m in Subject
Your models will be like.
subject_books = Table('subject_books', Base.metadata,
Column('subject_id', Integer, ForeignKey('subjects.id')),
Column('book_id', Integer, ForeignKey('books.id')),
)
subject_group = Table('subject_groups', Base.metadata,
Column('group_id', Integer, ForeignKey('groups.id')),
Column('subject_id', Integer, ForeignKey('subjects.id')),
)
class Subject(Base):
__tablename__ = 'subjects'
id = Column(Integer, primary_key=True)
value = Column(Unicode(255), unique=True)
groups = relationship('Groups', secondary=subject_groups, backref='subjects')
class Groups(Base):
__tablename__ = 'groups'
id = Column(Integer, primary_key=True)
name = Column(Unicode(255), unique=True)
class Book(Base):
__tablename__ = 'books'
id = Column(Integer, primary_key=True)
title = Column(Unicode(255))
isbn = Column(Unicode(24))
subjects = relationship('Subject', secondary=subject_books, backref='books')
I also check the docs for attribute_mapped_collection. But each time I found that each key is associated with only one object not more then one. If you read anywhere then please provide the link so I can check that how it will be fit in your code.
I think this will be help you.
I have read the SQLAlchemy documentation and tutorial about building many-to-many relation but I could not figure out how to do it properly when the association table contains more than the 2 foreign keys.
I have a table of items and every item has many details. Details can be the same on many items, so there is a many-to-many relation between items and details
I have the following:
class Item(Base):
__tablename__ = 'Item'
id = Column(Integer, primary_key=True)
name = Column(String(255))
description = Column(Text)
class Detail(Base):
__tablename__ = 'Detail'
id = Column(Integer, primary_key=True)
name = Column(String)
value = Column(String)
My association table is (It's defined before the other 2 in the code):
class ItemDetail(Base):
__tablename__ = 'ItemDetail'
id = Column(Integer, primary_key=True)
itemId = Column(Integer, ForeignKey('Item.id'))
detailId = Column(Integer, ForeignKey('Detail.id'))
endDate = Column(Date)
In the documentation, it's said that I need to use the "association object". I could not figure out how to use it properly, since it's mixed declarative with mapper forms and the examples seem not to be complete. I added the line:
details = relation(ItemDetail)
as a member of Item class and the line:
itemDetail = relation('Detail')
as a member of the association table, as described in the documentation.
when I do item = session.query(Item).first(), the item.details is not a list of Detail objects, but a list of ItemDetail objects.
How can I get details properly in Item objects, i.e., item.details should be a list of Detail objects?
From the comments I see you've found the answer. But the SQLAlchemy documentation is quite overwhelming for a 'new user' and I was struggling with the same question. So for future reference:
ItemDetail = Table('ItemDetail',
Column('id', Integer, primary_key=True),
Column('itemId', Integer, ForeignKey('Item.id')),
Column('detailId', Integer, ForeignKey('Detail.id')),
Column('endDate', Date))
class Item(Base):
__tablename__ = 'Item'
id = Column(Integer, primary_key=True)
name = Column(String(255))
description = Column(Text)
details = relationship('Detail', secondary=ItemDetail, backref='Item')
class Detail(Base):
__tablename__ = 'Detail'
id = Column(Integer, primary_key=True)
name = Column(String)
value = Column(String)
items = relationship('Item', secondary=ItemDetail, backref='Detail')
Like Miguel, I'm also using a Declarative approach for my junction table. However, I kept running into errors like
sqlalchemy.exc.ArgumentError: secondary argument <class 'main.ProjectUser'> passed to to relationship() User.projects must be a Table object or other FROM clause; can't send a mapped class directly as rows in 'secondary' are persisted independently of a class that is mapped to that same table.
With some fiddling, I was able to come up with the following. (Note my classes are different than OP's but the concept is the same.)
Example
Here's a full working example
from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
from sqlalchemy.orm import declarative_base, relationship, Session
# Make the engine
engine = create_engine("sqlite+pysqlite:///:memory:", future=True, echo=False)
# Make the DeclarativeMeta
Base = declarative_base()
class User(Base):
__tablename__ = "users"
id = Column(Integer, primary_key=True)
name = Column(String)
projects = relationship('Project', secondary='project_users', back_populates='users')
class Project(Base):
__tablename__ = "projects"
id = Column(Integer, primary_key=True)
name = Column(String)
users = relationship('User', secondary='project_users', back_populates='projects')
class ProjectUser(Base):
__tablename__ = "project_users"
id = Column(Integer, primary_key=True)
notes = Column(String, nullable=True)
user_id = Column(Integer, ForeignKey('users.id'))
project_id = Column(Integer, ForeignKey('projects.id'))
# Create the tables in the database
Base.metadata.create_all(engine)
# Test it
with Session(bind=engine) as session:
# add users
usr1 = User(name="bob")
session.add(usr1)
usr2 = User(name="alice")
session.add(usr2)
session.commit()
# add projects
prj1 = Project(name="Project 1")
session.add(prj1)
prj2 = Project(name="Project 2")
session.add(prj2)
session.commit()
# map users to projects
prj1.users = [usr1, usr2]
prj2.users = [usr2]
session.commit()
with Session(bind=engine) as session:
print(session.query(User).where(User.id == 1).one().projects)
print(session.query(Project).where(Project.id == 1).one().users)
Notes
reference the table name in the secondary argument like secondary='project_users' as opposed to secondary=ProjectUser
use back_populates instead of backref
I made a detailed writeup about this here.
Previous Answer worked for me, but I used a Class base approach for the table ItemDetail. This is the Sample code:
class ItemDetail(Base):
__tablename__ = 'ItemDetail'
id = Column(Integer, primary_key=True, index=True)
itemId = Column(Integer, ForeignKey('Item.id'))
detailId = Column(Integer, ForeignKey('Detail.id'))
endDate = Column(Date)
class Item(Base):
__tablename__ = 'Item'
id = Column(Integer, primary_key=True)
name = Column(String(255))
description = Column(Text)
details = relationship('Detail', secondary=ItemDetail.__table__, backref='Item')
class Detail(Base):
__tablename__ = 'Detail'
id = Column(Integer, primary_key=True)
name = Column(String)
value = Column(String)
items = relationship('Item', secondary=ItemDetail.__table__, backref='Detail')