I have a issue using SQLAlchemy.
Base = declarative_base()
node_to_node = Table("node_to_node", Base.metadata,
Column("left_node_id", Integer, ForeignKey("node.id"), primary_key=True),
Column("right_node_id", Integer, ForeignKey("node.id"), primary_key=True)
)
class Node(Base):
__tablename__ = 'node'
id = Column(Integer, primary_key=True)
label = Column(String)
right_nodes = relationship("Node",
secondary=node_to_node,
primaryjoin=id==node_to_node.c.left_node_id,
secondaryjoin=id==node_to_node.c.right_node_id,
backref="left_nodes"
)
metadata = Base.metadata
engine = create_engine("postgres+psycopg2://postgres:admin#localhost:5432/test")
Base.metadata.drop_all(engine)
Base.metadata.create_all(engine)
session = sessionmaker()
session.configure(bind=engine)
s = session()
node1 = Node(label="node1")
node2 = Node(label="node2")
node3 = Node(label="node3")
node1.right_nodes.append(node2)
node1.right_nodes.append(node3)
s.add_all([node1, node2, node3])
s.commit()
what I want is to have the IDs of all the right nodes of node 1 as an array, so here [2, 3]
Do you know a method that allows me to do that?
Thanks in advance for any help!
EDIT :
class NeedTag(Base):
__tablename__ = 'need_tags'
tag_id = Column(Integer, ForeignKey('tags.id'), primary_key=True)
text_id = Column(Integer, ForeignKey('texts.id'), primary_key=True)
class Text(Base) :
__tablename__ = 'texts'
id = Column(Integer, primary_key=True)
text = Column(Text, nullable=False)
need_tag = relationship("Tag",
secondary="need_tags")
class Tag(Base):
__tablename__ = 'tags'
id = Column(Integer, primary_key=True)
name = Column(String(), nullable=False)
I have a problem with the SQL Alchemy synthax.
For example, I defined the Text and Tags class and a many-to-many relationship between Text and Tags: To use a text, you need to have some tags that must be present.
An example of a condition is:
If tag1 or tag2 :
If tag3 or tag 4 :
Text1 can be used
I would like to do this:
text1.need_tags = [ [tag1, tag2],[tag3, tag4] ]
And therefore to use text1, you need at least 1 tag in the 1st list AND 1 tag in the 2nd list
But I tried so many techniques and they all failed
Do you know if it is possible to do that with SQLAlchemy ? Or something like that that accomplish the same thing
Related
Using SQLAlchemy I have three models: Parent1, Parent2, and Child, where Parent1 has one-to-one relationship with Parent2, and both of them has the same relationship with Child. Here are they:
from extensions import db_session
class Parent1(Base):
__tablename__ = 'parent1'
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
parent2 = relationship("Parent2", backref="parent1", uselist=False)
child = relationship("Child", backref="parent1", uselist=False)
class Parent2(Base):
__tablename__ = 'parent2'
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
parent1_id = Column(Integer, ForeignKey('parent1.id'))
child = relationship("Child", backref="parent2", uselist=False)
class Child(Base):
id = Column(Integer, primary_key=True)
parent1_id = Column(Integer, ForeignKey('parent1.id'))
parent2_id = Column(Integer, ForeignKey('parent2.id'))
What I am trying to achieve is to fill Child table with its parents' foreign keys.
So, when I execute this:
parent1 = Parent1(name="Adil")
parent1.parent2 = Parent2(name="Aisha")
parent1.child = Child()
db_session.add(parent1)
db_session.commit()
to the parents tables it inserts data as needed, however to the Child table it inserts data like this:
Child
id parent1_id parent2_id
1 1 NULL
How to properly set relationships, so that on any insert to the Parent1->Parent2 tables it also inserts its ids as foreign keys to Child table?
What I want to achieve is:
Child
id parent1_id parent2_id
1 1 1
I came up with this solution. I removed declared model Child and created association table between two models and added secondary parameter filling with assocation table name:
Base = declarative_base()
child = Table('child', Base.metadata,
Column('parent1_id', Integer, ForeignKey('parent1.id')),
Column('parent2_id', Integer, ForeignKey('parent2.id')))
class Parent1(Base):
__tablename__ = 'parent1'
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
parent2 = relationship("Parent2", secondary='child', uselist=False)
class Parent2(Base):
__tablename__ = 'parent2'
id = Column(Integer, primary_key=True)
name = Column(String, nullable=False)
parent1_id = Column(Integer, ForeignKey('parent1.id'))
I got 3 tables
class Article_Comment(Base):
__tablename__ = 'article_comment'
article_id = Column(Integer, ForeignKey('article.id'), primary_key=True)
comment_id = Column(Integer, ForeignKey('comment.id'), primary_key=True)
child = relationship("Comment", lazy="joined", innerjoin=True)
class Article(Base):
__tablename__ = 'article'
id = Column(Integer, primary_key=True)
title = Column(String)
children = relationship("Article_Comment", lazy="joined", innerjoin=True)
class Comment(Base):
__tablename__ = 'comment'
id = Column(Integer, primary_key=True)
text = Column(String)
I need to get specific Article with Comments. I do this like this:
Session = sessionmaker(bind=engine)
session = Session()
result = session.query(Article, Comment).join(Article_Comment).join(Comment).filter(Article_Comment.article_id == Article.id).filter(Article_Comment.comment_id == Comment.id).filter(Article.title=='music').all()
for i, j in result:
print i.title, j.text
But I want to make this query without using .join.
Can someone help me?
May be, I need to remake relationships?
My thx to univerio
Here is the full answer
set up a relationship on Article, comments = relationship(Comment, secondary=Article_Comment.__table__, lazy="joined")
session.query(Article).filter(Article.title=='music').one().comments
I have the following tables configured:
class User(Base):
__tablename__ = "user"
id = Column(Integer, primary_key=True)
name = Column(String)
class Gadget(Base):
__tablename__ = "gadget"
id = Column(Integer, primary_key=True)
brand = Column(String)
class UserGadget(Base):
__tablename__ = "user_gadget"
user_id = Column(Integer, ForeignKey('user.id'), primary_key=True)
gadget_id = Column(Integer, ForeignKey('gadget.id'), primary_key=True)
user = relationship("User", backref=backref('userGadgets', order_by=user_id))
gadget = relationship("Gadget", backref=backref('userGadgets', order_by=gadget_id))
class GadgetComponent(Base):
__tablename__ = "gadget_component"
id = Column(String, primary_key=True)
gadget_id = Column(Integer,ForeignKey('gadget.id'))
component_maker = Column(String)
host = relationship("Gadget", backref=backref('components', order_by=id))
class ComponentUsingMetal(Base):
__tablename__ = "component_metal"
id = Column(Integer, primary_key=True)
component_id = Column(Integer, ForeignKey('GadgetComponent.id'))
metal = Column(String)
component = relationship("GadgetComponent", backref=backref('gadgetComponentMetals', order_by=id))
On doing the following query:
session.query(User).join("userGadgets", "gadget", "components","gadgetComponentMetals").filter(ComponentUsingMetal.metal == 'iron') , component_metal gets attached to the query twice giving an error 'table name component_metal specified more than once'.
Any idea what I am doing wrong?
I traced the problem down to the following line in selectable.py:
froms = [f for f in froms if f not in toremove] This line removes the tables which are already covered by joins so that FROM clause doesn't have the same table specified more than once. The line didn't remove component_metal even though toremove had it meaning that I had two different Table objects for the same db table. And then I noticed the import for component_metal's class, ComponentUsingMetal, looked different. The others imports looked like:
from myschema import GadgetComponent
from myschema import Gadget
from python.myschema ComponentUsingMetal
As soon as fixed the import the issue went away.
I am using sqlalchemy to create a structure that resembles a graph, so that there are several types of nodes and links joining them. The nodes are defined like this:
class Node(Base):
__tablename__ = 'node'
id = Column(Integer, primary_key=True)
type = Column(Unicode)
__mapper_args__ = {'polymorphic_on': type}
class InputNode(Node):
__tablename__ = 'inputnode'
id = Column(Integer, ForeignKey('node.id'), primary_key=True)
__mapper_args__ = {'polymorphic_identity': 'input'}
class ThruNode(Node):
__tablename__ = 'thrunode'
id = Column(Integer, ForeignKey('node.id'), primary_key=True)
__mapper_args__ = {'polymorphic_identity': 'thru'}
class OutputNode(Node):
__tablename__ = 'outputnode'
id = Column(Integer, ForeignKey('node.id'), primary_key=True)
__mapper_args__ = {'polymorphic_identity': 'output'}
Now I want to create a Link table which would looks something like this:
class Link(Base):
__tablename__ = 'link'
input = Column(Integer, ForeignKey('node.id', where='type IN ("input", "thru")'))
output = Column(Integer, ForeignKey('node.id', where='type IN ("thru", "output")'))
The bit I'm struggling with is how to do the where part of it, since as I've written it is not valid in sqlalchemy. I had though of using a CheckConstraint or a ForeignKeyConstraint, but I can't see how either of them could actually be used to do this.
I haven't tryed it nor am I an expert of this, but shouldn't this work?
class Link(Base):
__tablename__ = 'link'
input = Column(Integer, ForeignKey('thrunode.id'))
output = Column(Integer, ForeignKey('outputnode.id'))
First I had another idea that maybe you could have used different names for the ids and than use those, kind of like:
instead of:
class InputNode(Node):
__tablename__ = 'inputnode'
id = Column(Integer, ForeignKey('node.id'), primary_key=True)
__mapper_args__ = {'polymorphic_identity': 'input'}
this:
class ThruNode(Node):
[...]
thrunode_id = Column(Integer, ForeignKey('node.id'), primary_key=True)
[...]
and then:
class Link(Base):
__tablename__ = 'link'
input = Column(Integer, ForeignKey('node.thrunode_id'))
output = Column(Integer, ForeignKey('node.outputnode_id'))
I got the idea from here sqlalchemy docs: declarative.html#joined-table-inheritance
I want to map a Tag entity using declarative method with SQLAlchemy. A tag can have a parent (another Tag).
I have:
class Tag(Base):
__tablename__ = 'tag'
id = Column(Integer, primary_key=True)
label = Column(String)
def __init__(self, label, parentTag=None):
self.label = label
How can I add the "parent" relationship?
You add a ForeignKey referencing the parent, and then create a relationship that specifies the direction via remote_side. This is documented under adjacency list relationships. For declarative you'd do something like this:
class Tag(Base):
__tablename__ = 'tag'
id = Column(Integer, primary_key=True)
label = Column(String)
parent_id = Column(Integer, ForeignKey('tag.id'))
parent = relationship('Tag', remote_side=[id])
If you want the reverse relation also, add backref='children' to the relationship definition.
If you need children, you need to use uselist:
class Tag(Base):
__tablename__ = 'tag'
id = Column(Integer, primary_key=True)
label = Column(String)
child_id = Column(Integer, ForeignKey('tag.id'))
children = relation('Tag', remote_side=[id], uselist=True)
class Company(BaseModel):
__tablename__ = 'companies'
companyName = db.Column(db.String(50))
contactPerson = db.Column(db.String(50))
email = db.Column(db.String(50))
mobile = db.Column(db.String(20))
parentID = db.Column(db.Integer, db.ForeignKey('companies.id')) # parent company ID
childrenCompany = db.relationship('Company', remote_side='Company.id',
backref=db.backref('children_company')) # parent Company
use:
In [2]: company_query = Company.query.get_or_404(1)
In [3]: company_query.children_company
Out[3]:
[<app.models.user.Company at 0x10f527850>,
<app.models.user.Company at 0x10f527c10>]
parent = relation('Tag') — see http://www.sqlalchemy.org/docs/05/reference/ext/declarative.html#configuring-relations.