I've seen a few questions similar to this but none quite hit the nail on the head. Essentially I have three table models Center(), Business(), and CenterBusiness() in a Flask Application using SQLAlchemy. Currently I'm adding to said relationship in this manner:
biz = Business(typId=form.type.data, name=form.name.data,
contact=form.contact.data, phone=form.phone.data)
db.session.add(biz)
db.session.commit()
assoc = CenterBusiness(bizId=biz.id, cenId=session['center'])
db.session.add(assoc)
db.session.commit()
As you can see that's a bit ugly and I know there is a way to do it in one hit with the relationship as they are defined. I see on SQLAlchemy's docs they have a explanation of working with such a table but I can't seem to get it to work.
#Directly from SQLAlchemy Docs
p = Parent()
a = Association(extra_data="some data")
a.child = Child()
p.children.append(a)
#My Version Using my Tables
center = Center.query.get(session['center']
assoc = CenterBusiness()
assoc.business = Business(typId=form.type.data, name=form.name.data,
contact=form.contact.data, phone=form.phone.data)
center.businesses.append(assoc)
db.session.commit()
Unfortunately, that doesn't seem to be doing the trick... Any help would be greatly appreciated and below I've posted the models involved.
class Center(db.Model):
id = db.Column(MEDIUMINT(8, unsigned=True), primary_key=True,
autoincrement=False)
phone = db.Column(VARCHAR(10), nullable=False)
location = db.Column(VARCHAR(255), nullable=False)
businesses = db.relationship('CenterBusiness', lazy='dynamic')
employees = db.relationship('CenterEmployee', lazy='dynamic')
class Business(db.Model):
id = db.Column(MEDIUMINT(8, unsigned=True), primary_key=True,
autoincrement=True)
typId = db.Column(TINYINT(2, unsigned=True),
db.ForeignKey('biz_type.id',
onupdate='RESTRICT',
ondelete='RESTRICT'),
nullable=False)
type = db.relationship('BizType', backref='businesses',
lazy='subquery')
name = db.Column(VARCHAR(255), nullable=False)
contact = db.Column(VARCHAR(255), nullable=False)
phone = db.Column(VARCHAR(10), nullable=False)
documents = db.relationship('Document', backref='business',
lazy='dynamic')
class CenterBusiness(db.Model):
cenId = db.Column(MEDIUMINT(8, unsigned=True),
db.ForeignKey('center.id',
onupdate='RESTRICT',
ondelete='RESTRICT'),
primary_key=True)
bizId = db.Column(MEDIUMINT(8, unsigned=True),
db.ForeignKey('business.id',
onupdate='RESTRICT',
ondelete='RESTRICT'),
primary_key=True)
info = db.relationship('Business', backref='centers',
lazy='joined')
archived = db.Column(TINYINT(1, unsigned=True), nullable=False,
server_default='0')
I was able to get this working, my problem lied in the following bit of code (error in bold):
#My Version Using my Tables
center = Center.query.get(session['center']
assoc = CenterBusiness()
**assoc.info** = Business(typId=form.type.data, name=form.name.data,
contact=form.contact.data, phone=form.phone.data)
center.businesses.append(assoc)
db.session.commit()
As explained in my comment in the question:
Alright my issue was that I was not using the relationship key "info"
I have in my CenterBusiness model to define the appended association.
I was saying center.business thinking that the term business in that
case was arbitrary. However, I needed to actually reference that
relationship. As such, the appropriate key I had setup already in
CenterBusiness was info.
I will still accept any updates and/or better ways to handle this situation, though I think this is the best route at the time.
below example can help u
more details http://docs.sqlalchemy.org/en/latest/orm/extensions/associationproxy.html
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String(64))
# association proxy of "user_keywords" collection
# to "keyword" attribute
keywords = association_proxy('user_keywords', 'keyword')
def __init__(self, name):
self.name = name
class UserKeyword(Base):
__tablename__ = 'user_keyword'
user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
keyword_id = Column(Integer, ForeignKey('keyword.id'), primary_key=True)
special_key = Column(String(50))
# bidirectional attribute/collection of "user"/"user_keywords"
user = relationship(User,
backref=backref("user_keywords",
cascade="all, delete-orphan")
)
# reference to the "Keyword" object
keyword = relationship("Keyword")
def __init__(self, keyword=None, user=None, special_key=None):
self.user = user
self.keyword = keyword
self.special_key = special_key
class Keyword(Base):
__tablename__ = 'keyword'
id = Column(Integer, primary_key=True)
keyword = Column('keyword', String(64))
def __init__(self, keyword):
self.keyword = keyword
def __repr__(self):
return 'Keyword(%s)' % repr(self.keyword)
Related
I seem to have a hard time locating an issue I have with the following many-to-many relationship:
class UserTable(Base):
__tablename__ = "user"
id = Column(String, primary_key=True)
name = Column(UnicodeText)
courses = relationship("CourseTable", secondary="user_course")
class CourseTable(Base):
__tablename__ = "course"
id = Column(String, primary_key=True)
title = Column(UnicodeText)
users = relationship("UserTable", secondary="user_course")
class UserCourseTable(Base):
__tablename__ = "user_course"
user_id = Column(String, ForeignKey('user.id'), primary_key=True)
course_id = Column(String, ForeignKey('course.id'), primary_key=True)
user = relationship("UserTable", backref=backref("user_course"))
course = relationship("CourseTable", backref=backref("user_course"))
When querying for User
user = await self.session.execute(
select(UserTable)
.where(UserTable.id == user_id)
)
I get the following error:
When initializing mapper mapped class UserCourseTable->user_course, expression 'CourseTable' failed to locate a name ('CourseTable'). If this is a class name, consider adding this relationship() to the <class 'app.models.db.user_course.UserCourseTable'> class after both dependent classes have been defined.
I tried everything described in their docs, but to no avail: the error still persists
Any suggestions?
Thanks!
EDIT:
SQLAlchemy==1.4.36
I am trying to build a model where there is the default values then there is the user defined values. So the default values would come from the spices table. Yes the spices table would contain default data. The user would define the composite spice and make modifications as desired for a specific recipe. If you think I am structuring this wrong please provide your expertise. I feel lost on how to do this.
class User(db.Model, UserMixin):
__tablename__ = 'user'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(100), nullable=True)
#... extra
#... extra
class Spice(db.Model):
__tablename__ = 'spices'
code = db.Column(db.String(5), primary_key=True) # this is the id code
name = db.Column(db.String(60))
origin = db.Column(db.String(15))
def __init__(self, code, name, origin):
self.code = code
self.name = name
self.origin = origin
class Seasoning(Spice):
__tablename__ = 'seasonings'
# Note that the below item should come from Recipe. How would I do this?
recipe_id = db.Column(db.Integer, db.ForeignKey('recipe.id'), nullable=False)
class Recipe(db.Model):
__tablename__ = 'recipe'
user = db.relationship(User)
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(60))
description = db.Column(db.Text(), nullable=False)
date = db.Column(db.DateTime, default=datetime.datetime.utcnow)
ingredient = db.relationship('Ingredient', backref='recipe', lazy='dynamic', primaryjoin="Recipe.id == Seasoning.recipe_id")
def __init__(self, id, name, description, date):
self.id = id
self.name = name
self.description = description
self.date = date
in my views.py I have
...
seasoning = Seasoning(code=from.code.data, name=form.name.data, origin=form.origin,
recipe_id=recipe_id)
db.session.add(seasoning)
db.create_all()
db.session.commit()
...
When I run this I do get an error when I try to commit() to seasoning. How do I resolve this?
sqlalchemy.exc.OperationalError: (raised as a result of Query-invoked
autoflush; consider using a session.no_autoflush block if this flush
is occurring prematurely) (sqlite3.OperationalError) table spices has
no column named recipe_id
You need to describe recipe_id in your spices class
table spices has no column named recipe_id
Context: I'm making an auctioning website for which I am using Flask-SQLAlchemy. My tables will need to have a many-to-many relationship (as one artpiece can have many user bids and a user can bid on many artpieces)
My question is: it is possible to add another column to my joining table to contain the id of the user bidding, the id of artpiece that they are bidding on and also how much they bid? Also if yes, how would I include this bid in the table when I add a record to said table?
bid_table = db.Table("bid_table",
db.Column("user_id", db.Integer, db.ForeignKey("user.user_id")),
db.Column("item_id", db.Integer, db.ForeignKey("artpiece.item_id"))
)
class User(db.Model):
user_id = db.Column(db.Integer, unique=True, primary_key=True, nullable=False)
username = db.Column(db.Integer, unique=True, nullable=False)
email = db.Column(db.String(50), unique =True, nullable=False)
password = db.Column(db.String(60), nullable=False)
creation_date = db.Column(db.DateTime, default=str(datetime.datetime.now()))
bids = db.relationship("Artpiece", secondary=bid_table, backref=db.backref("bids", lazy="dynamic"))
class Artpiece(db.Model):
item_id = db.Column(db.Integer, unique=True, primary_key=True, nullable=False)
artist = db.Column(db.String(40), nullable=False)
buyer = db.Column(db.String(40), nullable=False)
end_date = db.Column(db.String(40))
highest_bid = db.Column(db.String(40))
It is possible to do this with SQL Alchemy, but it's very cumbersome in my opinion.
SQLAlchemy uses a concept called an Association Proxy to turn a normal table into an association table. This table can have whatever data fields you want on it, but you have to manually tell SQLAlchemy which columns are foreign keys to the other two tables in question.
This is a good example from the documentation.
In your case, the UserKeyword table is the association proxy table that you want to build for your user/bid scenario.
The special_key column is the arbitrary data you would store like the bid amount.
from sqlalchemy import Column, Integer, String, ForeignKey
from sqlalchemy.ext.associationproxy import association_proxy
from sqlalchemy.orm import backref, declarative_base, relationship
Base = declarative_base()
class User(Base):
__tablename__ = 'user'
id = Column(Integer, primary_key=True)
name = Column(String(64))
# association proxy of "user_keywords" collection
# to "keyword" attribute
keywords = association_proxy('user_keywords', 'keyword')
def __init__(self, name):
self.name = name
class UserKeyword(Base):
__tablename__ = 'user_keyword'
user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
keyword_id = Column(Integer, ForeignKey('keyword.id'), primary_key=True)
special_key = Column(String(50))
# bidirectional attribute/collection of "user"/"user_keywords"
user = relationship(User,
backref=backref("user_keywords",
cascade="all, delete-orphan")
)
# reference to the "Keyword" object
keyword = relationship("Keyword")
def __init__(self, keyword=None, user=None, special_key=None):
self.user = user
self.keyword = keyword
self.special_key = special_key
class Keyword(Base):
__tablename__ = 'keyword'
id = Column(Integer, primary_key=True)
keyword = Column('keyword', String(64))
def __init__(self, keyword):
self.keyword = keyword
def __repr__(self):
return 'Keyword(%s)' % repr(self.keyword)
Check out the full documentation for instructions on how to access and create this kind of model.
Having used this in a real project, it's not particularly fun and if you can avoid it, I would recommend it.
https://docs.sqlalchemy.org/en/14/orm/extensions/associationproxy.html
While writing new test I found quite curious case:
models.ArticleTag(tag=tag, article=article)
Triggers INSERT statement on database even though there is no Session.add after.
However if I change code to look like this:
models.ArticleTag(tag.id=tag.id, article=article)
No INSERT will ever happen.
Article in this case is fresh object that is not in db yet and tag is something that we have already in db.
My models look like this:
class Tag(object):
__tablename__ = 'tag'
title = sqlalchemy.Column(sqlalchemy.Unicode(255), nullable=False)
type = sqlalchemy.Column(sqlalchemy.Unicode(255))
uid = sqlalchemy.Column(sqlalchemy.Unicode(32), primary_key=True, nullable=False)
__table_args__ = (
sqlalchemy.UniqueConstraint('type', 'title', name='title_type_unique'),
)
class ArticleTag(object):
"""Represent m2m table between Tags and Article.
association obj for mapping m2m articles<->tags
"""
__tablename__ = 'article_tag'
article_uid = sqlalchemy.Column(sqlalchemy.Unicode(32), sqlalchemy.ForeignKey('article.uid'), primary_key=True)
tag_uid = sqlalchemy.Column(sqlalchemy.Unicode(32), sqlalchemy.ForeignKey('tag.uid'), primary_key=True)
priority = sqlalchemy.Column(sqlalchemy.Integer, default=0)
tag = sqlalchemy.orm.relationship('Tag', backref='articles')
class Article(object):
__tablename__ = 'article'
uid = sqlalchemy.Column(sqlalchemy.Unicode(32), primary_key=True, nullable=False)
title = sqlalchemy.Column(sqlalchemy.Unicode(255), nullable=False)
meta_description = sqlalchemy.Column(sqlalchemy.Unicode(255))
meta_title = sqlalchemy.Column(sqlalchemy.Unicode(255))
body = sqlalchemy.Column(sqlalchemy.Unicode)
is_active = sqlalchemy.Column(sqlalchemy.Boolean, default=True)
# any tags we have
article_tags = sqlalchemy.orm.relationship('ArticleTag', backref='article', cascade='all, delete-orphan', order_by=lambda: sqlalchemy.desc(ArticleTag.priority))
#property
def tags(self):
"""Helper method that will return tags sorted by priority.
"""
return [art_tag.tag for art_tag in self.article_tags]
My guess is that I do not know something quite important about sqlalchemy.
Anyone can point me a direction?
I'm trying to create one-to-one and one-to-many relationship at the same time in Flask-SQLAlchemy. I want to achieve this:
"A group has many members and one administrator."
Here is what I did:
class Group(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(140), index=True, unique=True)
description = db.Column(db.Text)
created_at = db.Column(db.DateTime, server_default=db.func.now())
members = db.relationship('User', backref='group')
admin = db.relationship('User', backref='admin_group', uselist=False)
def __repr__(self):
return '<Group %r>' % (self.name)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
group_id = db.Column(db.Integer, db.ForeignKey('group.id'))
admin_group_id = db.Column(db.Integer, db.ForeignKey('group.id'))
created_at = db.Column(db.DateTime, server_default=db.func.now())
However I got an error:
sqlalchemy.exc.AmbiguousForeignKeysError: Could not determine join
condition between parent/child tables on relationship Group.members -
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.
Does anyone know how to do that properly?
The solution is to specify the foreign_keys argument on all relationships:
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
group_id = Column(Integer, ForeignKey('groups.id'))
admin_group_id = Column(Integer, ForeignKey('groups.id'))
class Group(Base):
__tablename__ = 'groups'
id = Column(Integer, primary_key=True)
members = relationship('User', backref='group', foreign_keys=[User.group_id])
admin = relationship('User', backref='admin_group', uselist=False, foreign_keys=[User.admin_group_id])
Perhaps consider the admin relation in the other direction to implement "a group has many members and one admin":
class User(Base):
__tablename__ = 'users'
id = Column(Integer, primary_key=True)
group_id = Column(Integer, ForeignKey('groups.id'))
group = relationship('Group', foreign_keys=[group_id], back_populates='members')
class Group(Base):
__tablename__ = 'groups'
id = Column(Integer, primary_key=True)
members = relationship('User', foreign_keys=[User.group_id], back_populates='group')
admin_user_id = Column(Integer, ForeignKey('users.id'))
admin = relationship('User', foreign_keys=[admin_user_id], post_update=True)
See note on post_update in the documentation. It is necessary when two models are mutually dependent, referencing each other.
The problem you're getting comes from the fact that you've defined two links between your classes - a User has a group_id (which is a Foreign Key), and a Group has an admin (which is also defined by a Foreign Key). If you remove the Foreign Key from the admin field the connection is no longer ambiguous and the relationship works. This is my solution to your problem (making the link one-to-one):
from app import db,app
class Group(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(140), index=True, unique=True)
description = db.Column(db.Text)
created_at = db.Column(db.DateTime, server_default=db.func.now())
admin_id = db.Column(db.Integer) #, db.ForeignKey('user.id'))
members = db.relationship('User', backref='group')
def admin(self):
return User.query.filter_by(id=self.admin_id).first()
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(80), unique=True)
group_id = db.Column(db.Integer, db.ForeignKey('group.id'))
created_at = db.Column(db.DateTime, server_default=db.func.now())
The one drawback to this is that the group object doesn't have a neat admin member object you can just use - you have to call the function group.admin() to retrieve the administrator. However, the group can have many members, but only one of them can be the administrator. Obviously there is no DB-level checking to ensure that the administrator is actually a member of the group, but you could add that check into a setter function - perhaps something like:
# setter method
def admin(self, user):
if user.group_id == self.id:
self.admin_id = user.id
# getter method
def admin(self):
return User.query.filter_by(id=self.admin_id).first()
Ok, I found a workaround for this problem finally. The many-to-many relationship can coexist with one-to-many relationship between the same two tables at the same time.
Here is the code:
groups_admins = db.Table('groups_admins',
db.Column('user_id', db.Integer, db.ForeignKey('user.id')),
db.Column('group_id', db.Integer, db.ForeignKey('group.id'))
)
class Group(db.Model):
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(140), index=True, unique=True)
description = db.Column(db.Text)
created_at = db.Column(db.DateTime, server_default=db.func.now())
members = db.relationship('User', backref='group')
admins = db.relationship('User',
secondary=groups_admins,
backref=db.backref('mod_groups', lazy='dynamic'),
lazy='dynamic')
def __repr__(self):
return '<Group %r>' % (self.name)
class User(db.Model):
id = db.Column(db.Integer, primary_key=True)
group_id = db.Column(db.Integer, db.ForeignKey('group.id'))
created_at = db.Column(db.DateTime, server_default=db.func.now())
I still want someone to tell me how to set one-to-many and one-to-one relationship at the same time, so I leave my answer here and won't accept it forever.
This link solved it for me
most important thing is to specify foreign_keys value in the relation as well as the primary join