I've the following class
class Comision(Base):
__tablename__ = 'comision'
id = Column(Integer, primary_key=True)
key = Column(Integer, default=process())
in the column key i've the def process and i need to make some operations with the primary key of that table, it is possible to pass it like argument?
Try
key = Column(Integer, default=process)
or
key = Column(Integer, default=lambda:process())
Defined as key = Column(Integer, default=process()), process() is called once only when class Comision is defined.
Take a look at Context-Sensitive Default Functions in http://docs.sqlalchemy.org/en/rel_0_8/core/defaults.html for more detail.
Related
I am trying to set-up a cascade delete on a join relationship. However, whenever I try to delete a post in my application, I receive an error saying that, "update or delete on table "post" violates foreign key constraint" Here is a photo of the error message:
Here is my code:
class Post(db.Model):
"""Blog posts"""
__tablename__ = "posts"
id = db.Column(db.Integer,
primary_key=True,
autoincrement=True)
title = db.Column(db.String(25),
nullable=False)
content = db.Column(db.String(500),
nullable=False)
created_at = db.Column(db.DateTime,
default=db.func.current_timestamp())
user_table = db.Column(db.Integer,
db.ForeignKey('users.id',
ondelete='CASCADE'))
tags = db.relationship('Tag',
secondary="post_tags",
back_populates="posts",
cascade="all, delete"
)
class Tag(db.Model):
__tablename__ = "tags"
id = db.Column(db.Integer,
primary_key=True,
autoincrement=True)
name = db.Column(db.String,
unique=True)
posts = db.relationship('Post',
secondary="post_tags",
back_populates="tags")
class Post_Tag(db.Model):
__tablename__ = "post_tags"
post_id = db.Column(db.Integer,
db.ForeignKey('posts.id'), primary_key=True)
tag_id = db.Column(db.Integer,
db.ForeignKey('tags.id'), primary_key=True)
Based on the documentation and other questions I've viewed, I seem to be setting this up correctly. What am I doing wrong here?
UPDATE
I can delete Tags, but cannot delete Posts
You may be recieving this error because you're using backref instead of back_populates...
Also, I'd suggest defining your relationship bidirectionally, meaning in both the parent Post and child Tag models. This allows cascade deletion to the secondary table with different rules depending on which object is being deleted.
The following changes to your models should fix the error you're receiving:
# Modify your tags relationship to the following:
class Post(db.Model):
...
tags = db.relationship(
'Tag',
secondary="post_tags",
back_populates="posts", # use back-populates instead of backref
cascade="all, delete"
)
# Also, define your relationship from your tag model
class Tag(db.Model):
__tablename__ = "tags"
id = db.Column(db.Integer, primary_key=True, autoincrement=True)
name = db.Column(db.String, unique=True)
posts = db.relationship(
'Post',
secondary="post_tags",
back_populates="tags", # use back-populates instead of backref
# When a parent ("post") is deleted, don't delete the tags...
passive_deletes=True
)
So I'm building an app and I'm trying to save new changes to my database but when I try to commit the changes in the flask using db.session.commit() it returns me the following error:
sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column 'products.country_id' could not find table 'countries' with which to generate a foreign key to target column 'id'
In my models.py I have the following:
from app import db
from . import db
from datetime import datetime
def now():
return datetime.now()
class Countries(db.Model):
__tablename__ = 'countries'
__table_args__ = {'schema': 'products_data'}
id = db.Column(db.Integer, primary_key=True, unique=True, autoincrement=True)
name = db.Column(db.String(255))
code = db.Column(db.String(45))
def __repr__(self):
return f'Id {self.id}'
class Categories(db.Model):
__tablename__ = 'categories'
__table_args__ = {'schema': 'products_data'}
id = db.Column(db.Integer, primary_key=True, unique=True, autoincrement=True)
name = db.Column(db.String(255))
def __repr__(self):
return f'Id {self.id}'
class Brands(db.Model):
__tablename__ = 'brands'
__table_args__ = {'schema': 'products_data'}
id = db.Column(db.Integer, primary_key=True, unique=True, autoincrement=True)
name = db.Column(db.String(255))
logo = db.Column(db.String(5000))
feed = db.Column(db.String(5000))
feed_type = db.Column(db.String(45))
category_id = db.Column(db.Integer, db.ForeignKey('categories.id'))
country_id = db.Column(db.Integer, db.ForeignKey('countries.id'))
awinmid = db.Column(db.Integer)
def __repr__(self):
return f'Id {self.id}'
class Products(db.Model):
__tablename__ = 'products'
__table_args__ = {'schema': 'products_data'}
id = db.Column(db.Integer, primary_key=True, unique=True, autoincrement=True)
name = db.Column(db.String(255))
url = db.Column(db.Text)
category_id = db.Column(db.Integer, db.ForeignKey('categories.id'))
country_id = db.Column(db.Integer, db.ForeignKey('countries.id'))
price = db.Column(db.Float)
currency = db.Column(db.String(45))
discount_price = db.Column(db.Float)
shipping = db.Column(db.Float)
brand_id = db.Column(db.Integer, db.ForeignKey('brands.id'))
Am I doing anything wrong when associating a column in products with a foreign key? This is the first time I encounter this error so I'm really lost on what to do right now.
To fix I just added the schema to the db.ForeignKey and it worked
Example:
db.ForeignKey('products_data.countries.id')
PS:
Not my idea. Just wanted to post the answer in case someone visits the post later with the same problem.
Gord Thompson thanks for the help!
First of all, I don t see any table Categories. Secondly, you copy pasted your schema from the Products table into your Countries one.
PS: By default sqlalchemy gives the tables the name of the class (lower cased). So your __tablename__='products' does nothing actually.
EDIT:
The problem with your code lies in how you set the __table_args__ attribute. You assign an object to it, which by their specifications is wrong.
Take a look at the following example and modify your code accordingly
__table_args__ = ({'schema': 'products_data'})
Also for further reference, take a look at this https://docs.sqlalchemy.org/en/13/orm/extensions/declarative/table_config.html
The columns of the primary key must be in specific order.
I see some code from document :
class User(Base):
__tablename__ = 'users'
id = Column(Integer)
__mapper_args__ = {
'primary_key':[id]
}
But it just does not work (I'm using mysql, and the id primary key will not be generated).
Any possible solutions?
In case columns are declared in the same order as they should be in the primary key:
class User(Base):
field1 = Column(Integer, primary_key=True)
field2 = Column(Integer, primary_key=True)
Otherwise declare it in __table_args__:
class User(Base):
field1 = Column(Integer)
field2 = Column(Integer)
__table_args__ = (
PrimaryKeyConstraint(field2, field1),
{},
)
I'm trying to make a self-referential many-to-many relationship (it means that Line can have many parent lines and many child lines) in sqlalchemy like this:
Base = declarative_base()
class Association(Base):
__tablename__ = 'association'
prev_id = Column(Integer, ForeignKey('line.id'), primary_key=True)
next_id = Column(Integer, ForeignKey('line.id'), primary_key=True)
class Line(Base):
__tablename__ = 'line'
id = Column(Integer, primary_key = True)
text = Column(Text)
condition = Column(Text)
action = Column(Text)
next_lines = relationship(Association, backref="prev_lines")
class Root(Base):
__tablename__ = 'root'
name = Column(String, primary_key = True)
start_line_id = Column(Integer, ForeignKey('line.id'))
start_line = relationship('Line')
But I get the following error:
sqlalchemy.exc.ArgumentError: Could not determine join condition between parent/
child tables on relationship Line.next_lines. Specify a 'primaryjoin' expressio
n. If 'secondary' is present, 'secondaryjoin' is needed as well.
Do you know how I could remedy this?
You should just need:
prev_lines = relationship(
Association,
backref="next_lines",
primaryjoin=id==Association.prev_id)
Since this specifies the next_lines back reference there is no need to have a next_lines relationship.
You can also do this using the remote_side parameter to a relationship: http://www.sqlalchemy.org/trac/browser/examples/adjacency_list/adjacency_list.py
The title may be not exactly, but I don't know how to express it.
I have 3 class: User, Question, Answer. The simple code is:
Session = scoped_session(sessionmaker())
Base = declarative_base()
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
questions = relationship('Question', backref="user")
answers = relationship('Answer', backref="user")
class Question(Base):
__tablename__ = 'questions'
id = Column(Integer, primary_key=True)
user_id = Column(Integer, ForeignKey('users.id'))
answers = relationship('Answer', backref="user")
class Answer(Base):
__tablename__ = 'answers'
user_id = Column(Integer, ForeignKey('users.id'))
question_id = Column(Integer, ForeignKey('questions.id'))
id = Column(Integer, primary_key=True)
Now, A user asked a question, so there will be an answer created:
user = get_user_from_session()
question = get_question(question_id)
# create answer
answer = Answer()
answer.user = user
answer.question = question
Session.add(answer) # !!!
Session.commit()
I hope the answer will be inserted to database, but unfortunately, there is an error reported:
AttributeError: 'module' object has no attribute '_sa_instance_state'
Is there something I've missed? How to fix it?
UPDATE
Thanks for #dhaffey, I've fixed the typos. I recreate a test file to test this, found no error happened again, but answer.user_id and answer.question_id are null in database after commit.
This is my code, you can run it directly.
from sqlalchemy import *
from sqlalchemy.orm import *
from sqlalchemy.ext.declarative import *
engine = create_engine('sqlite:///test.sqlite', echo=True)
Session = scoped_session(sessionmaker())
Base = declarative_base()
Base.metadata.bind=engine
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String)
questions = relationship('Question')
answers = relationship('Answer')
class Question(Base):
__tablename__ = 'questions'
id = Column(Integer, primary_key=True)
user_id = Column(Integer, ForeignKey('users.id'))
title = Column(String)
answers = relationship('Answer')
class Answer(Base):
__tablename__ = 'answers'
user_id = Column(Integer, ForeignKey('users.id'))
question_id = Column(Integer, ForeignKey('questions.id'))
id = Column(Integer, primary_key=True)
Base.metadata.create_all()
user = User()
user.name = 'aaa'
Session.add(user)
Session.flush()
question = Question()
question.title = 'ttt'
question.user = user
Session.add(question)
Session.flush()
answer = Answer()
answer.user = user
answer.question = question
Session.add(answer)
Session.commit()
print answer.id # not None
found = Session.query(Answer).filter_by(id=answer.id).one()
print found.user.name # not None
print found.question.title # not None
# !!! It seems all models are saved correctly,
# but please open the test.sqlite database, (not querying by sqlahchemy)
# the question.user_id and answer.user_id and answer.question_id are null
Your class declarations don't "compile" for me, so I'm wondering if you've run this code, and which SQLAlchemy version you're using if so. The line
user_id = Column(Integer, ForeignKey='users.id')
raises
sqlalchemy.exc.ArgumentError: Unknown arguments passed to Column: ['ForeignKey']
with SQLAlchemy 0.6.4. You're trying to declare the foreign key with a keyword argument, but the correct usage is to construct a ForeignKey object and pass it positionally, like this:
user_id = Column(Integer, ForeignKey('users.id'))
With the foreign keys fixed, your example works as expected for me.
Note that you don't need to explicitly provide the primaryjoin argument on these relationships when the corresponding foreign keys are appropriately declared - SQLAlchemy infers the correct join.