I try to add a record to a joined-inheritance table.
For some reason I cannot fathom, the dependent table is not INSERTed into.
## Inheritance test case.
from sqlalchemy import create_engine, Column, Integer, String, ForeignKey
from sqlalchemy.orm import Session, relationship, backref
from sqlalchemy.ext.declarative import declarative_base
Base = declarative_base()
class Employee(Base):
__tablename__ = 'personnel'
__mapper_args__ = { 'polymorphic_on': 'etyp' }
id = Column(Integer, primary_key=True)
name = Column(String(50))
etyp = Column(String(10))
class Engineer(Employee):
__mapper_args__ = { 'polymorphic_identity':'eng' }
__tablename__ = "engineers"
id = Column(Integer, ForeignKey(Employee.id), index=True)
eng_data = Column(String(50))
engine = create_engine('sqlite:///', echo=True)
Base.metadata.create_all(engine)
session = Session(bind=engine)
e1 = Engineer(name="wally", eng_data="lazy guy")
session.add(e1)
session.commit()
# note that the Engineer table is not INSERTed into
e1 = session.query(Employee).filter_by(name="wally").one()
# the next line triggers an exception because it tries to lookup
# the Engineer row, which is missing
print e1.eng_data
This is Python 2.7, sqlalchemy 0.9.4 (Debian testing).
Making engineers.id a primary key will solve the problem:
class Engineer(Employee):
# ...
id = Column(Integer, ForeignKey(Employee.id), primary_key=True)
Related
I'm trying to create a Self-Referential Many-to-Many Relationship. The example outlined in the SQLAlchemy documentation works great. Here are the models I created:
from sqlalchemy import Integer, ForeignKey, String, Column, Table
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
Base = declarative_base()
Table('NodeToNode', Base.metadata,
Column('leftNodeId', Integer, ForeignKey('Node.id'), primary_key=True),
Column('rightNodeId', Integer, ForeignKey('Node.id'), primary_key=True)
)
class Node(Base):
__tablename__ = 'Node'
id = Column(Integer, primary_key=True)
label = Column(String)
rightNodes = relationship('Node',
secondary='NodeToNode',
primaryjoin='Node.id==NodeToNode.c.leftNodeId',
secondaryjoin='Node.id==NodeToNode.c.rightNodeId',
backref='leftNodes'
)
And the script for adding data in:
from sqlalchemy import create_engine
from sqlalchemy.orm import Session
engine = create_engine('sqlite:///practice.sqlite3')
session = Session(bind=engine)
nodes = [
Node(label='A'),
Node(label='B'),
Node(label='C'),
Node(label='D'),
Node(label='E'),
]
nodes[0].rightNodes = [nodes[1], nodes[3], nodes[2]]
nodes[0].leftNodes = [nodes[4]]
session.add_all(nodes)
session.commit()
I want to add a column to the association table so I'd assume I need to convert the association table to its own class:
class NodeToNode(Base):
__tablename__ = 'NodeToNode'
leftNodeId = Column(Integer, ForeignKey('Node.id', onupdate='CASCADE'), primary_key=True)
rightNodeId = Column(Integer, ForeignKey('Node.id', onupdate='CASCADE'), primary_key=True)
sortOrder = Column(Integer, nullable=False)
This, however, results in the following error:
sqlalchemy.exc.InvalidRequestError: Class <class 'models.node.NodeToNode'> does not have a mapped column named 'c'
Any idea what I'm doing wrong here?
I have this design
# coding: utf-8
from sqlalchemy import Column, VARCHAR, ForeignKey, create_engine
from sqlalchemy.dialects.mysql import INTEGER, TINYINT
from sqlalchemy.orm import relationship, sessionmaker
from sqlalchemy.inspection import inspect
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.ext.associationproxy import association_proxy
engine = create_engine('mysql://root:toor#localhost/test', echo=True)
Model = declarative_base()
Session = sessionmaker(bind=engine)
session = Session()
class A(Model):
__tablename__ = 'A'
id = Column(INTEGER(unsigned=True), primary_key=True)
name = Column(VARCHAR(32), nullable=False, index=True)
class AB(Model):
__tablename__ = 'AB'
A_id = Column(INTEGER(10, unsigned=True), ForeignKey('A.id'), nullable=False, primary_key=True)
B_id = Column(INTEGER(10, unsigned=True), ForeignKey('B.id'), nullable=False, primary_key=True)
type = Column(TINYINT(3, unsigned=True), nullable=False)
A_rel = relationship(
"A",
foreign_keys=[A_id]
)
B_rel = relationship(
"B",
foreign_keys=[B_id],
)
mapper_AB = inspect(AB)
class B(Model):
__tablename__ = 'B'
id = Column(INTEGER(10, unsigned=True), primary_key=True)
As = relationship("A", secondary=mapper_AB.local_table, uselist=False)
ABs = relationship("AB")
type = association_proxy('ABs', 'type')
Model.metadata.create_all(engine)
a = A(
name="test",
)
session.add(a)
session.commit()
b = B(
As=a,
type=2
)
print(b.type)
session.add(b)
session.commit()
This obviously fails, but I am trying to simplify the design by adding the AB extra information (type) via one (B) of the related classes constructor.
I have gone through tons of SQLAlchemy documentation, and even lost myself inside the source code but to no avail. The 3 table design of the database cannot be modified, as is part of a bigger system and belongs to another project. My goal is to map those table into a more simplified design for further development where this models will be used.
Is this possible using SQLAlchemy mechanisms with declarative style?
I have the following database schema:
Parent table:
id - primary key identifier.
type - polymorphic_identity.
name - string data column.
Child table - inherits Parent:
id - primary key identifier.
parent_id - foreignkey to Parent.
category - string data column.
Summing up I have two tables. Table Child inherits from Parent and also have a foreignkey to it.
UPD: I really need both inheritance and foreignkey. This example is only a short demo which reproduces the problem.
I used declarative_base to declare the schema:
# -*- coding: utf-8 -*-
from sqlalchemy import Column, String, Integer, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
Base = declarative_base()
class Parent(Base):
__tablename__ = "Parent"
id = Column(Integer, primary_key=True)
type = Column(String(250))
name = Column(String(250))
__mapper_args__ = {
'polymorphic_identity':'Parent',
'polymorphic_on':type
}
class Child(Parent):
__tablename__ = 'Child'
id = Column(Integer, ForeignKey('Parent.id'), primary_key=True)
parent_id = Column(ForeignKey("Parent.id"), nullable=True)
category = Column(String(250))
__mapper_args__ = {
'polymorphic_identity':'Child',
}
engine = create_engine('postgresql+psycopg2://joe:joe#localhost/alch')
session = sessionmaker()
session.configure(bind=engine)
Base.metadata.create_all(engine)
But when I run the code I get the following error:
sqlalchemy.exc.AmbiguousForeignKeysError: Can't determine join between 'Parent' and 'Child'; tables have more than one foreign key constraint relationship between them. Please specify the 'onclause' of this join explicitly.
I have tried to set relationship attribute myself for Parent or for Child separately and for both too. Tried to use primaryjoin and foreign_keys parameters of relationship. But the error was the same.
I'm totally confused about this error.
I need help.
I found the solution here.
SQLAlchemy needs a hint in this situation: a inherit_condition field in Child's __mapper_args__ does the trick.
# -*- coding: utf-8 -*-
from sqlalchemy import Column, String, Integer, ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy import create_engine
from sqlalchemy.orm import sessionmaker
Base = declarative_base()
class Parent(Base):
__tablename__ = "Parent"
id = Column(Integer, primary_key=True)
type = Column(String(250))
name = Column(String(250))
__mapper_args__ = {
'polymorphic_identity':'Parent',
'polymorphic_on':type
}
class Child(Parent):
__tablename__ = 'Child'
id = Column(Integer, ForeignKey('Parent.id'), primary_key=True)
parent_id = Column(ForeignKey("Parent.id"), nullable=True)
category = Column(String(250))
parent = relationship(Parent, foreign_keys=[parent_id])
__mapper_args__ = {
'polymorphic_identity':'Child',
'inherit_condition': id == Parent.id,
}
engine = create_engine('postgresql+psycopg2://joe:joe#localhost/alch')
session = sessionmaker()
session.configure(bind=engine)
Base.metadata.create_all(engine)
Have you tried removing the Foreign Key for the Child id field?
id = Column(Integer, ForeignKey('Parent.id'), primary_key=True)
parent_id = Column(ForeignKey("Parent.id"), nullable=True)
You need something like this:
id = Column(Integer, auto_increment=True, primary_key=True)
parent_id = Column(ForeignKey("Parent.id"), nullable=True)
I'm building an inheritance table schema like the following:
Spec Code
class Person(Base):
__tablename__ = 'people'
id = Column(Integer, primary_key=True)
discriminator = Column('type', String(50))
updated = Column(DateTime, server_default=func.now(), onupdate=func.now())
name = Column(String(50))
__mapper_args__ = {'polymorphic_on': discriminator}
class Engineer(Person):
__mapper_args__ = {'polymorphic_identity': 'engineer'}
start_date = Column(DateTime)
class Manager(Person):
__mapper_args__ = {'polymorphic_identity': 'manager'}
start_date = Column(DateTime)
UPDATED (WORKING) CODE
import os
import sys
from sqlalchemy import Column, create_engine, ForeignKey, Integer, String, DateTime
from sqlalchemy.orm import sessionmaker
from sqlalchemy.sql import func
from sqlalchemy.ext.declarative import declarative_base
try:
os.remove('test.db')
except FileNotFoundError:
pass
engine = create_engine('sqlite:///test.db', echo=True)
Session = sessionmaker(engine)
Base = declarative_base()
class People(Base):
__tablename__ = 'people'
discriminator = Column('type', String(50))
__mapper_args__ = {'polymorphic_on': discriminator}
id = Column(Integer, primary_key=True)
name = Column(String(50))
updated = Column(DateTime, server_default=func.now(), onupdate=func.now())
class Engineer(People):
__tablename__ = 'engineer'
__mapper_args__ = {'polymorphic_identity': 'engineer'}
id = Column(Integer, ForeignKey('people.id'), primary_key=True)
kind = Column(String(100), nullable=True)
Base.metadata.create_all(engine)
session = Session()
e = Engineer()
e.name = 'Mike'
session.add(e)
session.flush()
session.commit()
# works when updating the object
e.name = "Doug"
session.add(e)
session.commit()
# works using the base class for the query
count = session.query(People).filter(
People.name.is_('Doug')).update({People.name: 'James'})
# fails when using the derived class
count = session.query(Engineer).filter(
Engineer.name.is_('James')).update({Engineer.name: 'Mary'})
session.commit()
print("Count: {}".format(count))
Note: this is slightly modified example from sql docs
If I try to update the name for Engineer two things should happen.
update statement to the People table on column name
automatic trigger of update to the updated column on the People table
For now, i'd like to focus on number 1. Things like the example below (as also documented in the full code example) will result in invalid SQL
session.query(Engineer).filter(
Engineer.name.is_('James')).update({Engineer.name: 'Mary'})
I believe the above generates the following:
UPDATE engineer SET name=?, updated=CURRENT_TIMESTAMP FROM people WHERE people.name IS ?
Again, this is invalid. The statement is trying to update rows in incorrect table. name is in the base table.
I'm a little unclear about how inheritance tables should work but it seems like updates should work transparently with the derived object. Meaning, when I update Engineer.name querying against the Engineer object SQLAlchemy should know to update the People table. To complicate things a bit more, what happens if I try to update columns which exist in two tables
session.query(Engineer).filter(
Engineer.name.is_('James')).update({Engineer.name: 'Mary', Engineer.start_date: '1997-01-01'})
I suspect SQLAlchemy will not issue two update statements.
I have a model Region and each Region can have sub-regions. Each sub-region has a field parent_id which is the id of its parent region. Here is how my model looks like
class Region(db.Model):
__tablename__ = 'regions'
__table_args__ = {'schema': 'schema_name'}
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(100))
parent_id = db.Column(db.Integer, db.ForeignKey('regions.id'))
parent = db.relationship('Region', primaryjoin=('Region.parent_id==Region.id'), backref='sub-regions')
created_at = db.Column(db.DateTime, default=db.func.now())
deleted_at = db.Column(db.DateTime)
Bu when i try to do db.create_all i get this error sqlalchemy.exc.NoReferencedTableError: Foreign key associated with column 'regions.parent_id' could not find table 'regions' with which to generate a foreign key to target column 'id'
Why cant it find regions when i am specifying it in __tablename__? I am using flask-sqlalchemy version 1.0
EDIT --
i removed the line
__table_args__ = {'schema': 'schema_name'}
from my code and it works. Beats the hell out of me.
You must tell SQLAlchemy what the "remote side" of the relationship is, to distinguish between the current row and the row being joined to. The relevant explanation is located partway into this section of the documentation on relationships.
The relationship might look like this:
parent = db.relationship('Region', remote_side=id, backref='sub_regions')
This is an example demonstrating a self-referential relationship:
from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.engine import create_engine
from sqlalchemy.ext.declarative.api import declarative_base
from sqlalchemy.orm import sessionmaker, relationship
engine = create_engine('sqlite:///:memory:', echo=True)
Session = sessionmaker(engine)
Base = declarative_base(engine)
session = Session()
class Region(Base):
__tablename__ = 'region'
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
parent_id = Column(Integer, ForeignKey('region.id'), index=True)
parent = relationship(lambda: Region, remote_side=id, backref='sub_regions')
Base.metadata.create_all()
r1 = Region(name='United States of America')
r2 = Region(name='California', parent=r1)
session.add_all((r1, r2))
session.commit()
ca = session.query(Region).filter_by(name='California').first()
print ca.parent.name
There will be many lines of SQL output since echo is on, and the script will print 'United States of America' at the end.
I had the same issue with the schema name argument. What I changed to get it to work was to reference the table class directly in ForeignKey and relationships instead of using a string.
Example:
parent_id = Column(Integer, ForeignKey(Region.id), index=True)
parent = relationship(lambda: Region, remote_side=id, backref='sub_regions')
If you use a schema for any table, other tables that have foreign keys referencing those schema tables must provide the name of the schema. See the docs here
class Table(db.Model):
__tablename__ = 'table_1_name'
__table_args__ = {'schema': 'my_schema'}
id = Column('id', Integer, primary_key=True)
...
class AnotherTable(db.Model):
__tablename__ = 'table_2_name'
# Doesn't matter if this belongs to the same or different schema
# __table_args__ = {'schema': 'my_schema'}
id = Column('id', Integer, primary_key=True)
t1_id = Column(Integer, ForeignKey('my_schema.table_1_name.id'))
...
Works for both SQLAlchemy and Flask-SQLAlchemy. Hope this helps. :D
I only see slight differences from #davidism, but here's what works for me in straight SQLAlchemy.
from sqlalchemy import Column
from sqlalchemy import Integer
from sqlalchemy import ForeignKey
from sqlalchemy.orm import relationship
from sqlalchemy.orm import backref
class Region(Base):
__tablename__ = 'region'
id = Column(Integer, primary_key=True)
parent_id = Column(Integer, ForeignKey('region.id'), index=True)
sub_regions = relationship('Region', backref=backref('parent', remote_side='Region.id'))
As he points out I'm guessing you wont need the imports, but should prefix them with db, so something like:
class Region(db.Model):
__tablename__ = 'region'
id = db.Column(db.Integer, primary_key=True)
parent_id = db.Column(db.Integer, db.ForeignKey('region.id'), index=True)
sub_regions = db.relationship('Region', backref=db.backref('parent', remote_side='Region.id'))