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Flask SQLAlchemy Association Table: error creating backref

I have a Artist model, and a Venue model, and they have a many-to-many relationship facilitated by the Show model (the shows indicate the artist, venue and date of the concert).
class Venue(db.Model):
__tablename__ = 'Venue'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String, unique=True, nullable=False)
shows = db.relationship('Show', backref='venue', lazy=True)
class Artist(db.Model):
__tablename__ = 'Artist'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String, unique=True, nullable=False)
shows = db.relationship('Show', backref='artist', lazy=True)
class Show(db.Model):
__tablename__ = 'Show'
id = db.Column(db.Integer, primary_key=True)
venue_id = db.Column(db.Integer, db.ForeignKey('Venue.id'), nullable=False)
artist_id = db.Column(db.Integer, db.ForeignKey('Artist.id'), nullable=False)
start_time = db.Column(db.DateTime, nullable=False)
venue = db.relationship('Venue', back_populates='venue')
artist = db.relationship('Artist', back_populates='artist')
I'd like to have a query to get the venue name, artist name, and date of all upcoming shows so had in mind the following...
upcoming_shows = Show.query.filter_by(show.start_time >= datetime.now()).all()
...so that I can then access for example, upcoming_shows[0].Venue.name, upcoming_shows[0].Artist.name and upcoming_shows[0].start_time.
That query however returns the following:
sqlalchemy.exc.ArgumentError: Error creating backref 'venue' on
relationship 'Venue.shows': property of that name exists on mapper
'mapped class Show->Show'
Feel like I'm close but missing something fundamental!

Solved. I made the changes below to the code and it works now. It was rather straight-forward in the end, I simply had to ensure that the relationship names were unique :-\
class Venue(db.Model):
__tablename__ = 'Venue'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String, unique=True, nullable=False)
venue_shows = db.relationship('Show', back_populates='venue', lazy=True)
class Artist(db.Model):
__tablename__ = 'Artist'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String, unique=True, nullable=False)
artist_shows = db.relationship('Show', back_populates='artist', lazy=True)
class Show(db.Model):
__tablename__ = 'Show'
id = db.Column(db.Integer, primary_key=True)
venue_id = db.Column(db.Integer, db.ForeignKey('Venue.id'), nullable=False)
artist_id = db.Column(db.Integer, db.ForeignKey('Artist.id'), nullable=False)
start_time = db.Column(db.DateTime, nullable=False)
venue = db.relationship('Venue', back_populates='venue_shows')
artist = db.relationship('Artist', back_populates='venue_artist')

Here is a general example for what you are looking for
class Association(Base):
__tablename__ = 'association'
left_id = Column(Integer, ForeignKey('left.id'), primary_key=True)
right_id = Column(Integer, ForeignKey('right.id'), primary_key=True)
extra_data = Column(String(50))
child = relationship("Child", back_populates="parents")
parent = relationship("Parent", back_populates="children")
class Parent(Base):
__tablename__ = 'left'
id = Column(Integer, primary_key=True)
children = relationship("Association", back_populates="parent")
class Child(Base):
__tablename__ = 'right'
id = Column(Integer, primary_key=True)
parents = relationship("Association", back_populates="child")
For more details check the documentation

Writing a composite Key in Flask SQL Alchemy [duplicate]

This question already has answers here:
sqlalchemy unique across multiple columns
(4 answers)
Closed 3 years ago.
I have my table like something below:
class Dummies(db.Model):
__tablename__ = 'dummies'
id = db.Column(db.Integer, primary_key=True, autoincrement=True)
name = db.Column(db.String(100), index=True, nullable=True)
value = db.Column(db.String(100), index=True, nullable=True)
sum_id = db.Column(db.Integer, db.ForeignKey('pattern.id',
onupdate='CASCADE',
ondelete='CASCADE'),
index=True, nullable=False)
I am quite new to flask and trying to get around the syntax for this relationship, I want to represent. I want to use the name, value and sum_id to uniquely represent a row. Could someone help me how to write the relationship for this ?

If you want enforce the unique constraint on multiple columns you can explicitly set it like this:
__tablename__ = 'dummies'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(100), nullable=True)
value = db.Column(db.String(100), nullable=True)
sum_id = db.Column(db.Integer, db.ForeignKey('pattern.id'), nullable=False)
UniqueConstraint('name', 'value', 'sum_id'
name='myMultipleColumnUniqueConstraint')
This way you can enforce multiple column unique constraint. Also just wanted point out that
onupdate => refers to a default value for the column.
There is no ondelete in sqlAlchemy as far as I know. but you can use:
cascade = "all, delete-orphan" ```
on Parent Table relationship to achieve the same effect as ondelete="cascade" as in django.
class ParentDummies(db.Model):
dummies= relationship("Dummy", cascade="all, delete-orphan")
Also, if you are trying make those columns as composite primary key, you can do so like this:
``` class Dummies(db.Model):
__tablename__ = 'dummies'
id = db.Column(db.Integer)
name = db.Column(db.String(100), nullable=True)
value = db.Column(db.String(100), nullable=True)
sum_id = db.Column(db.Integer, db.ForeignKey('pattern.id', nullable=False),
PrimaryKeyConstrain('name', 'value', 'sum_id', name="myCompositePk")
OR
class Dummies(db.Model):
__tablename__ = 'dummies'
id = db.Column(db.Integer, primary_key=True, autoincrement=True)
name = db.Column(db.String(100), nullable=True, primary_key=True)
value = db.Column(db.String(100), nullable=True, primary_key=True)
sum_id = db.Column(db.Integer, db.ForeignKey('pattern.id'), nullable=False, primary_key=True)

How can I attach generic `Contact` to multiple different tables?

I'm trying to create a set of tables which can all have a Contactassigned to them.
class Contact(Base):
__tablename__ = "contact"
id = Column(Integer, primary_key=True)
name = Column(String, index=True, nullable=False, doc="Name of the contact.")
phone = Column(String, index=True, doc="Phone number of the contact.")
Contacts can be linked to from various other tables, and one record can have more than one contact in different fields.
class BusinessGroup(Base):
__tablename__ = "business_group"
id = Column(Integer, primary_key=True)
name = Column(String, index=True, nullable=False, doc="Name of the group.")
main_contact = Column(Integer, ForeignKey("contact.id"), doc="Main contact details for the group.")
second_contact = Column(Integer, ForeignKey("contact.id"), doc="Second contact details for the group.")
class Vendor(Base):
__tablename__ = "vendor"
id = Column(Integer, primary_key=True)
name = Column(String, index=True, nullable=False, doc="Name of the vendor.")
contact = Column(Integer, ForeignKey("contact.id"), doc="Main contact details for the vendor.")
This setup seems to work, but in flask-admin, no contact fields show up when creating a new item for either BusinessGroup or Vendor.
How can I make this design work? Or should I be modelling this kind of relationship in a different way entirely?

I ended up subclassing the Contact table so that I could have:
class MainContact(Contact):
__tablename__ = "main_contact"
id = Column(Integer, ForeignKey("contact.id"), primary_key=True)
business_group = relationship("BusinessGroup", back_populates="main_contact")
business_group_id = Column(Integer, ForeignKey("business_group.id"), nullable=False)
...
class SecondContact(Contact):
__tablename__ = "second_contact"
id = Column(Integer, ForeignKey("contact.id"), primary_key=True)
business_group = relationship("BusinessGroup", back_populates="second_contact")
business_group_id = Column(Integer, ForeignKey("business_group.id"), nullable=False)
...
class BusinessGroup(Base):
__tablename__ = "business_group"
id = Column(Integer, primary_key=True)
name = Column(String, index=True, nullable=False, doc="Name of the group.")
main_contact = relationship(
"MainContact", back_populates="business_group", uselist=False,
doc="Main contact details for the business_group."
)
second_contact = relationship(
"SecondContact", back_populates="business_group", uselist=False,
doc="Second contact details for the business_group."
)
As well as requiring subclassing so that we can have two different contacts referred to from the same model, the other important part was adding the foreign key relationships, so that the contacts show up in the Flask Admin panel.

How to set relationship between two tables in SQLAlchemy?

I have got two tables:
Announcements
AnnouncementsSchedule
Relationship is one(Announcements) to many(AnnouncementsSchedule) by keys:
Announcements.id = AnnouncementsSchedule.announcements_id
I tried to describe models in SQLAlchemy:
The first table is described as model:
class Announcements(db.Model):
__tablename__ = 'announcements'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(150), nullable=False)
text = db.Column(db.Text(), nullable=False)
category = db.Column(db.Integer(), nullable=False)
subcategory = db.Column(db.Integer(), nullable=False)
offer_type = db.Column(db.Integer(), nullable=False)
url = db.Column(db.String(150), nullable=True)
status = db.Column(db.Integer(), nullable=False)
#children = relationship("AnnouncementsSchedule", back_populates="announcements")
Second is:
class AnnouncementsSchedule(db.Model):
__tablename__ = 'announcements_schedule'
id = Column(Integer, primary_key=True)
week_day = db.Column(db.Integer(), nullable=True)
week_all = db.Column(db.Integer(), nullable=False)
time = db.Column(db.Time(), nullable=False)
announcement_id = Column(Integer, ForeignKey('announcements.announcements_id'))
What I do wrong?

You have a mistake in the column name (announcements doesn't have announcement_id ):
# announcement_id = Column(Integer, ForeignKey('announcements.announcements_id'))
# change to ->
announcement_id = Column(Integer, ForeignKey('announcements.id'))

How to inserting data into interrelated relationship tables using SQLAlchemy (not flask_sqlalchemy or flask-merge)?

I am new to SQLAlchemy, I am trying to build a practice project using SQLAlchemy. I have created the database containing tables with the following relationship. Now my questions are :
How to INSERT data into the tables as they are interdependent?
Does this form a loop in database design?
Is the looping database design, a bad practice? How to resolve this if its a bad practice?
Department.manager_ssn ==> Employee.SSN
and
Employee.department_id ==> Department.deptid
database relationship diagram
and following is the current version of code creating this exact database.
# Department table
class Departments(Base):
__tablename__ = "Departments"
# Attricutes
Dname= Column(String(15), nullable=False)
Dnumber= Column(Integer, primary_key=True)
Mgr_SSN= Column(Integer, ForeignKey('Employees.ssn'), nullable=False)
employees = relationship("Employees")
# Employee table
class Employees(Base):
__tablename__ = "Employees"
# Attributes
Fname = Column(String(30), nullable=False)
Minit = Column(String(15), nullable=False)
Lname = Column(String(15), nullable=False)
SSN = Column(Integer, primary_key=True)
Bdate = Column(Date, nullable=False)
Address = Column(String(15), nullable=False)
Sex = Column(String(1), default='F', nullable=False)
Salary = Column(Integer, nullable=False)
Dno = Column(Integer, ForeignKey('Departments.Dnumber'), nullable=False)
departments = relationship("Departments")
Please provide the solution in SQLAlchemy only and not in flask-sqlalchemy or flask-migrate and I am using Python 3.6.

You can avoid such circular reference design altogether by
Declaring the foreign key constraint on just one side of the relationship
Use a boolean flag to denote if the employee is a manager
class Department(Base):
__tablename__ = 'departments'
department_id = Column(Integer, primary_key=True)
employees = relationship('Employee', lazy='dynamic', back_populates='department')
class Employee(Base):
__tablename__ = 'employees'
employee_id = Column(Integer, primary_key=True)
is_manager = Column(Boolean, nullable=False, default=False)
department_id = Column(Integer, ForeignKey('departments.department_id'), nullable=False)
department = relationship('Department', back_populates='employees')
You can find the manager of the department using
department = session.query(Department).get(..)
department.employees.filter(Employee.is_manager == True).one_or_none()