I am trying to do a many-to-many relationship table with more information than just the two ids. It doesnt work. I obviously standardised my table with generic names. But the use case could be like a user table , with a post table and a likes relationship table, something like that. when i do these table, python gave me that :
sqlalchemy.exc.NoForeignKeysError: Could not determine join condition between parent/child tables on relationship Table2.rela1 - there are no foreign keys linking these tables. Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or specify a 'primaryjoin' expression.
So here is my relationship table
class Relationship(db.Model):
id = db.Column(db.Integer, primary_key = True)
table1_id = db.Column(db.Integer, db.ForeignKey('Table1.id')),
table2_id = db.Column(db.Integer, db.ForeignKey('Table2.id')),
value = db.Column(db.Integer), #a number
date = db.Column(db.DateTime) #actual time of the entry
here is my table1
class Table1(db.Model):
id = db.Column(db.Integer, primary_key = True)
rela1 = db.relationship('Relationship', backref = 'rel1', lazy = 'dynamic')
rela2 = db.relationship('Table2', backref = 'rel2', lazy = 'dynamic')
here is my table 2
class Table2(db.Model):
id = db.Column(db.Integer, primary_key = True)
table1_id = db.Column(db.Integer, db.ForeignKey('table1.id'))
rela1 = db.relationship('Relationship', backref = 'rel3', lazy = 'dynamic')
Thanks for helping me.
If that can be solved then my second issue is creating a function to compute the total 'value' per Table2 object, regardless of the which table1 object post the value. something like a select with sum and group by table2.id , but i dont really understand how to do it with python and flask and sqlalchemy.
Thanks.
EDIT1
Using http://docs.sqlalchemy.org/en/rel_0_9/orm/relationships.html#association-object
i changed to
class Relationship(db.Model):
__tablename__ = 'relationship'
table1_id = db.Column(db.Integer, db.ForeignKey('Table1.id'), primary_key = True),
table2_id = db.Column(db.Integer, db.ForeignKey('Table2.id'), primary_key = True),
value = db.Column(db.Integer), #a number
date = db.Column(db.DateTime) #actual time of the entry
table2obj = db.relationship("Table2", backref="table2_assocs")
then
class Table2(db.Model):
__tablename__ = 'table2'
id = db.Column(db.Integer, primary_key = True)
table1_id = db.Column(db.Integer, db.ForeignKey('table1.id'))
and table 1 is unchanged except the addition of tablename
but now i get
sqlalchemy.exc.ArgumentError: Mapper Mapper|Relationship|relatioship could not assemble any primary key columns for mapped table 'Relationship'
there are two relationship declarations on Table1, but from the code you've posted, I can see only one path to Table2, through Relationship.table2_id.
It looks like you are trying to have a many-to-many relationship with extra metadata on the intermediate relation. This is called the association object pattern in the sqlalchemy docs. For that, everything you've got so far, except the Table1.rela2 is good, you pretty well have it. That "rogue" relationship needs to be removed.
to get the convenience of having a real relationship from Table1 to Table2, you need to use an association proxy.
Related
Please note: this question is related but separate from my other currently open question SQLAlchemy secondary join relationship on multiple foreign keys.
The SQLAlchemy documentation describes handling multiple join paths in a single class for multiple relationships:
from sqlalchemy import Integer, ForeignKey, String, Column
from sqlalchemy.ext.declarative import declarative_base
from sqlalchemy.orm import relationship
Base = declarative_base()
class Customer(Base):
__tablename__ = 'customer'
id = Column(Integer, primary_key=True)
name = Column(String)
billing_address_id = Column(Integer, ForeignKey("address.id"))
shipping_address_id = Column(Integer, ForeignKey("address.id"))
billing_address = relationship("Address")
shipping_address = relationship("Address")
class Address(Base):
__tablename__ = 'address'
id = Column(Integer, primary_key=True)
street = Column(String)
city = Column(String)
state = Column(String)
zip = Column(String)
Within the same section the documentation shows three separate ways to define the relationship:
billing_address = relationship("Address", foreign_keys=[billing_address_id])
billing_address = relationship("Address", foreign_keys="[Customer.billing_address_id]")
billing_address = relationship("Address", foreign_keys="Customer.billing_address_id")
As you can see in (1) and (2) SQLAlchemy allows you to define a list of foreign_keys. In fact, the documentation explicitly states:
In this specific example, the list is not necessary in any case as there’s only one Column we need: billing_address = relationship("Address", foreign_keys="Customer.billing_address_id")
But I cannot determine how to use the list notation to specify multiple foreign keys in a single relationship.
For the classes
class PostVersion(db.Model):
id = db.Column(db.Integer, primary_key=True)
...
tag_1_id = db.Column(db.Integer, db.ForeignKey("tag.id"))
tag_2_id = db.Column(db.Integer, db.ForeignKey("tag.id"))
tag_3_id = db.Column(db.Integer, db.ForeignKey("tag.id"))
tag_4_id = db.Column(db.Integer, db.ForeignKey("tag.id"))
tag_5_id = db.Column(db.Integer, db.ForeignKey("tag.id"))
class Tag(db.Model):
id = db.Column(db.Integer, primary_key=True)
tag = db.Column(db.String(127))
I have tried all of the following:
tags = db.relationship("Tag", foreign_keys=[tag_1_id, tag_2_id, tag_3_id, tag_4_id, tag_5_id]) resulting in
sqlalchemy.exc.AmbiguousForeignKeysError: Could not determine join condition between parent/child tables on relationship AnnotationVersion.tags - there are multiple foreign key paths linking the tables. Specify the 'foreign_keys' argument, providing a list of those columns which should be counted as containing a foreign key reference to the parent table.
tags = db.relationship("Tag", foreign_keys="[tag_1_id, tag_2_id, tag_3_id, tag_4_id, tag_5_id]") resulting in
sqlalchemy.exc.InvalidRequestError: When initializing mapper Mapper|AnnotationVersion|annotation_version, expression '[tag_1_id, tag_2_id, tag_3_id, tag_4_id, tag_5_id]' failed to locate a name ("name 'tag_1_id' is not defined"). If this is a class name, consider adding this relationship() to the class after both dependent classes have been defined.
And many others variations on the list style, using quotes inside and outside, using Table names and Class names.
I've actually solved the problem in the course of this question. Since there seems to be no direct documentation, I'll answer it myself instead of deleting this question.
The key is to define the relationship on a primary join and specify the uselist parameter.
tags = db.relationship("Tag", primaryjoin="or_(PostVersion.tag_1_id==Tag.id,"
"PostVersion.tag_2_id==Tag.id, PostVersion.tag_3_id==Tag.id,"
"PostVersion.tag_4_id==Tag.id, PostVersion.tag_5_id==Tag.id)",
uselist=True)
I am in the process of working with sqlalchemy and MySQL to build a database. I am currently having trouble defining a specific relationship between two tables.
class Experiment_Type(Base):
__tablename__='experiment_types'
id = Column(Integer, primary_key=True)
type = Column(String(100))
class Experiments(Base):
__tablename__ = 'experiments'
id = Column(Integer, primary_key=True)
type = Column(String(100))
sub_id = Column(Integer, ForeignKey('experiment_types.id'))
experiments = relationship('Experiments',
primaryjoin="and_(Experiment_Type.id == Experiments.sub_id,
'Experiments.type' == 'Experiment_Type.type')",
backref=backref('link'))
What I want to do is have values of sub_id in experiments match the id in experiment_types based on type (if an entry in experiment_types of type = 'type1' has id = 1, then an entry in experiments with type = 'type1' should have a sub_id = 1). I am not even sure if this is the best way to approach defining the relationship in this situation
so any advice is welcome.
The current error message is this:
sqlalchemy.exc.ArgumentError: Could not locate any relevant foreign key columns for primary join condition '0 = 1' on relationship Experiments.experiments. Ensure that referencing columns are associated with a ForeignKey or ForeignKeyConstraint, or are annotated in the join condition with the foreign() annotation.
The whole point of setting up relationships in relational dbs is to not have to duplicate data across tables. Just do something like this:
class ExperimentType(Base):
__tablename__='experiment_types'
id = Column(Integer, primary_key=True)
name = Column(String(100))
class Experiments(Base):
__tablename__ = 'experiments'
id = Column(Integer, primary_key=True)
description = Column(String(100))
type_id = Column(Integer, ForeignKey('experiment_types.id'))
type = relationship("ExperimentType")
Then, if you do need to display the experiment type stuff later, can access it with something like:
exp = session.query(Experiment).first()
print exp.type.name
I have two models in SQLAlchemy, having a many-to-many relationship
team_user_table = Table('team_user', Base.metadata,
Column('user_id', Integer, ForeignKey('users.id')),
Column('team_id', Integer, ForeignKey('teams.id'))
)
class User(Base):
""" The SQLAlchemy declarative model class for a User object. """
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
name = Column(String, unique=True)
class Team(Base):
""" The SQLAlchemy declarative model class for a Team object. """
__tablename__ = 'teams'
id = Column(Integer, primary_key=True)
name = Column(Text, unique=True)
members = relationship("User",
secondary=team_user_table,
backref="memberteams")
I would like to query those users that are not member of a specific team.
In SQL (for example):
SELECT u.id,u.name FROM users u WHERE u.id NOT IN (SELECT tu.user_id FROM team_user tu WHERE tu.team_id=?);
How can I do this in SQLAlchemy?
This does what you want:
team_id = 1
query = session.query(User.id).filter(~User.memberteams.any(Team.id == team_id))
This is the SQL it outputs (on MySQL):
SELECT users.id AS users_id, users.name AS users_name
FROM users
WHERE NOT (EXISTS (SELECT 1
FROM team_user, teams
WHERE users.id = team_user.user_id AND teams.id = team_user.team_id AND teams.id = %s))
This is not exactly what your query looks like now, but I think this is the way it should be done. Check the docs for this.
I tested this on MySQL. However, I think it should work on any other.
To have the exact query you are looking for, you might need to look into using subqueries in combination with the filter statement. I think you will need explicit reference to the team_user table in your code to make it work.
I believe this should work and it does not use subqueries.
session.query(User).join(team_users_table).filter(team_users_table.team_id != OTHER_TEAM)
I'm trying to perform a query that works across a many->many relation ship between bmarks and tags with a secondary table of bmarks_tags. The query involves several subqueries and I have a need to DISTINCT a column. I later want to join that to another table via the DISTINCT'd ids.
I've tried it a few ways and this seems closest:
tagid = alias(Tag.tid.distinct())
test = select([bmarks_tags.c.bmark_id],
from_obj=[bmarks_tags.join(DBSession.query(tagid.label('tagid'))),
bmarks_tags.c.tag_id == tagid])
return DBSession.execute(qry)
But I get an error:
⇝ AttributeError: '_UnaryExpression' object has no attribute 'named_with_column'
Does anyone know how I can perform the join across the bmarks_tags.tag_id and the result of the Tag.tid.distinct()?
Thanks
Schema:
# this is the secondary table that ties bmarks to tags
bmarks_tags = Table('bmark_tags', Base.metadata,
Column('bmark_id', Integer, ForeignKey('bmarks.bid'), primary_key=True),
Column('tag_id', Integer, ForeignKey('tags.tid'), primary_key=True)
)
class Tag(Base):
"""Bookmarks can have many many tags"""
__tablename__ = "tags"
tid = Column(Integer, autoincrement=True, primary_key=True)
name = Column(Unicode(255), unique=True)
Something like this should work:
t = DBSession.query(Tag.tid.distinct().label('tid')).subquery('t')
test = select([bmarks_tags.c.bmark_id], bmarks_tags.c.tag_id == t.c.tid)
return DBSession.execute(test)
It is hard to tell what you are trying to accomplish, but since you are using orm anyways (and there is not much reason anymore to go with bare selects in sa these days), you should probably start by establishing a many-to-many relation:
bmarks_tags = Table('bmark_tags', Base.metadata,
Column('bmark_id', Integer, ForeignKey('bmarks.bid'), primary_key=True),
Column('tag_id', Integer, ForeignKey('tags.tid'), primary_key=True)
)
class Tag(Base):
"""Bookmarks can have many many tags"""
__tablename__ = "tags"
tid = Column(Integer, primary_key=True)
name = Column(Unicode(255), unique=True)
class BMark(Base):
__tablename__ = 'bmarks'
bid = Column(Integer, primary_key=True)
tags = relation(Tag, secondary=bmarks_tags, backref="bmarks")
Then get your query and go from there:
query = DBSession.query(BMark).join(BMark.tags)
If not, give us the actual sql you are trying to make sqlalchemy emit.
I have a simple One-to-Many relation mapped with SqlAlchemy:
Base = declarative_base()
class Type(Base):
__tablename__ = "entity_types"
type = Column(String(100), primary_key=True)
description = Column(String(300))
class Entity(Base):
__tablename__ = "entities"
id = Column(Integer, primary_key=True)
type_id = Column('type', String(100), ForeignKey(Types.type),
nullable=False)
type = relation(Type, backref='entities')
value = Column(Text, nullable=False)
I want to query all types ever used in an entity. In pure SQL I would accomplish this by:
SELECT entity_types.*
FROM entities
JOIN entity_types ON entities.type == entity_types.type
GROUP BY entity_types.type
How do I solve this using SqlAlchemy's ORM-Engine?
I've tried these queries, but they all don't return what I want:
session.query(Action.type).group_by(Action.type).all()
session.query(Type).select_from(Action).group_by(Type).all()
I've also tried using options(joinedload('type')), but I found out, this is only used to force eager loading and to bypass lazy-loading.
ADDITION: I've just added the backref in the relation of Entity. I think the problem is solvable by querying count(Type.entities) > 0, but I cannot figure out how to exactly form a valid ORM query.
I've just figured it out:
session.query(ActionType).filter(ActionType.actions.any()).all()
The any() does the trick.