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sqlalchemy column_property in self-referential

I can't describe the column "invited_name" (column_property). I don't know how to do this correctly.
class Worker(declarative_base()):
__tablename__ = "staff_worker_info"
id = Column(Integer, primary_key=True)
first_name = Column(String(40), nullable=False)
last_name = Column(String(40), nullable=False)
invited_id = Column(Integer, ForeignKey('staff_worker_info.id'))
invited = relationship("Worker", uselist=False, remote_side=[id], join_depth=1)
# I don't know how to describe this column
invited_name = column_property(
select([Worker.first_name]). \
where(Worker.id == invited_id).\
label('invited_n'))
I understand why this doesn't work, but I don't know how to write it differently.
I should get such a SQL query.
SELECT staff_worker_info.id, staff_worker_info.first_name staff_worker_info.last_name, staff_worker_info.invited_id,
(SELECT worker_invited.first_name
FROM staff_worker_info AS worker_invited
WHERE staff_worker_info.invited_id = worker_invited.id) AS invited_n,
FROM staff_worker_info

Might be a bit late, but I recently faced a similar question. I think your problem is quite easy to solve with only the relationship. If you want you can also solve it by using a column_property.
First, using the relationship. If you make the invited relationship joined, then the actual query that is send to the database is a self-join. You can access the first name via that relationship (reference https://docs.sqlalchemy.org/en/14/orm/self_referential.html).
class Worker(declarative_base()):
__tablename__ = "staff_worker_info"
id = Column(Integer, primary_key=True)
first_name = Column(String(40), nullable=False)
last_name = Column(String(40), nullable=False)
invited_id = Column(Integer, ForeignKey('staff_worker_info.id'))
invited = relationship("Worker", uselist=False, remote_side=[id], join_depth=1, lazy='joined')
#property
def invited_name(self):
return self.invited.first_name
Then, if the query you want to do is more complex, and it requires you to create a column_property, you can also do it as follows (reference https://docs.sqlalchemy.org/en/14/orm/mapped_sql_expr.html):
from sqlalchemy import inspect
from sqlalchemy.orm import aliased
class Worker(declarative_base()):
__tablename__ = "staff_worker_info"
id = Column(Integer, primary_key=True)
first_name = Column(String(40), nullable=False)
last_name = Column(String(40), nullable=False)
invited_id = Column(Integer, ForeignKey('staff_worker_info.id'))
invited = relationship("Worker", uselist=False, remote_side=[id], join_depth=1)
# Requires alias
worker = aliased(Worker)
inspect(Worker).add_property(
"invited_name",
column_property(
select([worker.first_name]). \
where(worker.id == Worker.invited_id)
)
)

I found a method. But he did not like it.
invited_name = column_property(
select([text("invited_table.first_name")]).
where(text("invited_table.id = staff_worker_info.invited_id")).
select_from(text("staff_worker_info AS invited_table")).
label('invited_n'))

Sqlalchemy: Can't execute sync rule (in many to many relationship)

I am struggling with "many to many" relationships in Sqlalchemy.
My data model:
a chain consists of one or multiple jobs
a job may be part of one or multiple chains
class Chain(Base):
__tablename__ = "chain"
__table_args__ = {'extend_existing': True}
__guarded__ = ['id']
id = Column(Integer, primary_key=True)
name = Column(Text, nullable=False)
# .. some other fields
class JobConfig(Base):
__tablename__ = "jobconfiguration"
__table_args__ = {'extend_existing': True}
__guarded__ = ['id']
chain = relationship("Chain", secondary='chain_job')
id = Column(Integer, primary_key=True)
jobname = Column(String(250).evaluates_none(), nullable=False, unique=True)
# some other fields
class ChainJob(Base):
__tablename__ = "chain_job"
__table_args__ = {'extend_existing': True}
__guarded__ = ['id']
id = Column(Integer, primary_key=True)
chain_id = Column(Integer, ForeignKey('chain.id'))
job_id = Column(Integer, ForeignKey('jobconfiguration.id'))
Now when I try to create a new chain and append a new job I get an error message:
chain = Chain()
chain.name='MyFirstChain'
job = JobConfig()
job.jobname="PartOfChain1"
job.chain.append(chain)
session.add(job)
session.add(chain)
session.commit()
sqlalchemy.orm.exc.UnmappedColumnError: Can't execute sync rule for
source column 'jobconfiguration.id'; mapper 'mapped class
JobConfig->jobconfiguration' does not map this column. Try using an
explicit foreign_keys collection which does not include destination
column 'chain_job.job_id' (or use a viewonly=True relation).
How can I fix this?

SQLAlchemy column_property basics

I have two models:
class Report(Base):
__tablename__ = 'report'
id = Column(Integer, primary_key=True)
class ReportPhoto(Base):
__tablename__ = 'report_photo'
id = Column(Integer, primary_key=True)
report_id = Column(Integer, ForeignKey(Report.id), nullable=False)
report = relationship(Report, uselist=False, backref=backref('report_photo', uselist=True))
And I would like to add column to Report model which indicates is there any records within ReportPhoto. I try to use column_property this way:
class Report(Base):
__tablename__ = 'report'
id = Column(Integer, primary_key=True)
has_photo = column_property(
select(ReportPhoto.any())
)
but get an error NameError: name 'ReportPhoto' is not defined. How I can fix this issue?

something like that should work:
class ReportPhoto(Base):
__tablename__ = 'report_photo'
id = Column(Integer, primary_key=True)
report_id = Column(Integer, ForeignKey('report.id'), nullable=False)
class Report(Base):
__tablename__ = 'report'
id = Column(Integer, primary_key=True)
report_photos = relationship(ReportPhoto, backref='report')
has_photo = column_property(
exists().where(ReportPhoto.report_id==id)
)

I will add to #Vladimir lliev's response with some clarification for anyone else that might not see how to do this.
Place the table that will have the 'foreign table referencing' column_property after that which it references. In this case, it means placing Report after ReportPhoto. This will solve your NameError, however, you would be left with a new error on your ReportPhoto foreign key reference. To solve this, place your foreign key table reference in quotes. You can read more by referencing the declarative documentation (e.g., declarative.py) and looking under "Configuring Relationships" --- specifically, read the portion on quoting your foreign references.
With your code, this would look like:
class ReportPhoto(Base):
# This now goes first
__tablename__ = 'report_photo'
id = Column(Integer, primary_key=True)
# Notice the quotations around Report references here
report_id = Column(Integer, ForeignKey("Report.id"), nullable=False)
# Notice the quotations around Report references here
report = relationship("Report",
uselist=False,
backref=backref("report_photo", uselist=True))
class Report(Base):
# This is now _after_ ReportPhoto
__tablename__ = 'report'
id = Column(Integer, primary_key=True)
# ReportPhoto now exists and we will not trip a NameError exception
has_photo = column_property(
select(ReportPhoto.any())
)

Sqlalchemy many to many mapping with extra fields

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.

How to build many-to-many relations using SQLAlchemy: a good example

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')