I use flask-sqlalchemy on a Flask project to model my database.
I need to sort the elements of a many-to-many relationship based on properties of different child elements of one side.
I have "Work" (the parent element), "Tag" (the children), "Type" (a one-to-many relationship on Tag) and "Block" (a one-to-many relationship on Type). Tags and Works are joined with a mapping table "work_tag_mapping".
In essence, each tag has exactly one type, each type belongs to exactly one block, and many tags can be added on many works.
I now want the list of tags on a work be sorted by block first and type second (both have a "position" column for that purpose).
Here are my tables (simplified for the sake of the question):
class Work(db.Model):
__tablename__ = 'work'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(255, collation='utf8_bin'))
tags = db.relationship('Tag', order_by="Tag.type.block.position, Tag.type.position", secondary=work_tag_mapping)
class Tag(db.Model):
__tablename__ = 'tag'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(255, collation='utf8_bin'))
type_id = db.Column(db.Integer, db.ForeignKey('type.id'), nullable=False)
type = db.relationship('Type')
work_tag_mapping = db.Table('work_tag_mapping',
db.Column('id', db.Integer, primary_key=True),
db.Column('work_id', db.Integer, db.ForeignKey('work.id'), nullable=False),
db.Column('tag_id', db.Integer, db.ForeignKey('tag.id'), nullable=False)
)
class Type(db.Model):
__tablename__ = 'type'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(255, collation='utf8_bin'))
position = db.Column(db.Integer)
block_id = db.Column(db.Integer, db.ForeignKey('block.id'), nullable=False)
block = db.relationship('Block')
class Block(db.Model):
__tablename__ = 'block'
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(255, collation='utf8_bin'))
position = db.Column(db.Integer)
Now, it is the "order_by" in the "tags" relationship that doesn't work as I initially hoped.
The error I get is "sqlalchemy.exc.InvalidRequestError: Property 'type' is not an instance of ColumnProperty (i.e. does not correspond directly to a Column)."
I am new to SQLalchemy, Flask and indeed Python, and none of the ressources or questions here mention a case like this.
While this appears not to be possible directly, adding a getter and performing the sorting on retrieval does the trick. Adding lazy='dynamic' ensures the collection behaves as a query, so joins can be performed.
_tags = db.relationship('Tag', lazy='dynamic')
#hybrid_property
def tags(self):
return self._tags.join(Type).join(Block).order_by(Block.position, Type.position)
Related
So I have a parent child relationship between Topic models with the relationship represented by this class:
class ParentChildRelation(db.Model):
__tablename__ = 'parent_child_relation'
id = db.Column(db.Integer, primary_key=True)
child_topic_id = db.Column(db.Integer, db.ForeignKey('topic.id'), nullable=False)
parent_topic_id = db.Column(db.Integer, db.ForeignKey('topic.id'), nullable=False)
And the topics defined as such:
class Topic(db.Model):
__tablename__ = 'topic'
id = db.Column(db.Integer, primary_key=True)
parent = db.relationship(
'Topic',
secondary='parent_child_relation',
primaryjoin='Topic.id == ParentChildRelation.child_topic_id',
secondaryjoin='Topic.id == ParentChildRelation.parent_topic_id'
)
I'd like to have parent be a one-to-one relationship for now (I might change it later on), but it comes back as an InstrumentedList. Is there a simple way of stating that parent should be a one-to-one relationship such that it links directly to a Topic model instead of being an InstrumentedList?
So it turns out I had previously found the correct answer, but I must have had a typo :/. Adding uselist=False did the trick.
parent = db.relationship(
'Topic',
secondary='parent_child_relation',
primaryjoin='Topic.id == ParentChildRelation.child_topic_id',
secondaryjoin='Topic.id == ParentChildRelation.parent_topic_id',
uselist=False
)
I have a SQLAlchemy model named NoteType with a relationship named sections. The NoteSection table is joined to the NoteType table through NoteTypeToSectionMap.
I want the sections list on the NoteType model to be ordered by the position field on the NoteTypeToSectionMap model. The code I have below seems to randomly be ordering the sections.
Does anyone know how to get the ordering to work?
Thanks!
class NoteType(ModelAbstract):
__tablename__ = "noteType"
id = db.Column(db.Integer, primary_key=True)
name = db.Column(db.String(255))
description = db.Column(db.String(255))
sections = db.relationship("NoteSection",
secondary=NoteTypeToSectionMap.__table__,
primaryjoin=id==NoteTypeToSectionMap.__table__.c.noteTypeId,
secondaryjoin=id==NoteTypeToSectionMap.__table__.c.noteSectionId,
order_by=NoteTypeToSectionMap.__table__.c.position)
-
class NoteTypeToSectionMap(ModelAbstract):
__tablename__ = "noteTypeToSectionMap"
id = db.Column(db.Integer, primary_key=True)
noteTypeId = db.Column(db.Integer, db.ForeignKey("noteType.id"))
noteSectionId = db.Column(db.Integer, db.ForeignKey("noteSection.id"))
position = db.Column(db.Integer)
Re-write the relationship as follows.
sections = db.relationship("NoteSection",
secondary=NoteTypeToSectionMap.__table__,
order_by=NoteTypeToSectionMap.__table__.c.position)
Situation
I have the Self-Referential Many-to-Many Relationship (almost identical to the sqlalchemy manual entry of the same heading). This relationship is governed by the table entity_weights. This code works!
Question
How do I include an attribute in class Entity representing the table column entity_weights.weight. Lets say the attribute would be called Entity.child_weights. It is important that the rank of Entity.child_entities and Entity.child_weights are identical.
entity_weights = Table('entity_weights', Base.metadata,
Column('id',Integer, primary_key=True),
Column('parent_entity_id',Integer, ForeignKey('entity.id')),
Column('entity_id',Integer, ForeignKey('entity.id')),
Column('weight',Float))
class Entity(Base):
__tablename__ = 'entity'
id = Column(Integer, primary_key=True)
name = Column(String)
domicile_id = Column(Integer, ForeignKey('domicile.id'))
entity_type = Column('type',Enum('asset','institution','model'))
source_table_id = Column(Integer)
child_entities = relationship('Entity',
secondary=entity_weights,
primaryjoin=id==entity_weights.c.parent_entity_id,
secondaryjoin=id==entity_weights.c.entity_id,
backref='parent_entity_id'
)
The cleanest solution I've found for this scenario is to break up the child_entities relationship by adding entity_weights as a one-to-many relationship on Entity and use an association proxy to proxy the weight value as well as the remote side of the many-to-many relationship:
class EntityWeight(Base):
__tablename__ = "entity_weights"
id = Column(Integer, primary_key=True)
parent_entity_id = Column(Integer, ForeignKey('entity.id'))
entity_id = Column(Integer, ForeignKey('entity.id'))
weight = Column(Float)
entity = relationship("Entity", primaryjoin=lambda: EntityWeight.entity_id == Entity.id)
class Entity(Base):
...
_child_weights = relationship(EntityWeight, primaryjoin=id == EntityWeight.parent_entity_id)
child_weights = association_proxy("_child_weights", "weight")
child_entities = association_proxy("_child_weights", "entity")
I have two models, related with many-to-many, one of them is hierarchical model:
#hierarchical model
class Tag(Base):
__tablename__ = "tags"
id = Column(Integer, primary_key=True)
name = Column(String)
Tag.parent_id = Column(Integer, ForeignKey(Tag.id, ondelete='CASCADE'))
Tag.childs = relationship(Tag, backref=backref('parent', remote_side=[Tag.id]),
cascade="all, delete")
class Subject(Base):
__tablename__ = "subjects"
id = Column(Integer, primary_key=True, doc="ID")
name = Column(String)
tags = relationship(Tag, secondary="tags_subjects", backref="subjects")
#many-to-many relations model
class TagsSubjects(Base):
__tablename__ = "tags_subjects"
id = Column(Integer, primary_key=True)
tag_id = Column(Integer, ForeignKey("tags.id"))
subject_id = Column(Integer, ForeignKey("subjects.id"))
So, I'll try to explain what I want to do... I want to make one (or several) query, for search all Subject's objects,
that have 'name' field value like 'foo' OR that has related tags having names with values like 'foo'
OR that has related tags, that has one or more parents (or above by hierarchy) tag with 'name' value like 'foo'
I've tried to do somethis like this:
>>> subjects = session.query(Subject).filter(or_(
Subject.name.ilike('%{0}%'.format('foo')),
Subject.tags.any(
Tag.name.ilike('%{0}%'.format('foo')))
)).order_by(Subject.name).all()
But it isn't correct and "flat" query, without hierarchical feature :(
How to do this by SQLAlchemy's API?
Thanks!
P.S. I'm using SQLite backend
My Python / SQLAlchemy application manages a set of nodes, all derived from a base class Node. I'm using SQLAlchemy's polymorphism features to manage
the nodes in a SQLite3 table. Here's the definition of the base Node class:
class Node(db.Base):
__tablename__ = 'nodes'
id = Column(Integer, primary_key=True)
node_type = Column(String(40))
title = Column(UnicodeText)
__mapper_args__ = {'polymorphic_on': node_type}
and, as an example, one of the derived classes, NoteNode:
class NoteNode(Node):
__mapper_args__ = {'polymorphic_identity': 'note'}
__tablename__ = 'nodes_note'
id = Column(None,ForeignKey('nodes.id'),primary_key=True)
content_type = Column(String)
content = Column(UnicodeText)
Now I need a new kind of node, ListNode, that is an ordered container of zero or more Nodes. When I load a ListNode, I want it to have its ID and title
(from the base Node class) along with a collection of its contained (child) nodes. A Node may appear in more than one ListNode, so it's not a proper hierarchy. I would create them along these lines:
note1 = NoteNode(title=u"Note 1", content_type="text/text", content=u"I am note #1")
session.add(note1)
note2 = NoteNode(title=u"Note 2", content_type="text/text", content=u"I am note #2")
session.add(note2)
list1 = ListNode(title=u"My List")
list1.items = [note1,note2]
session.add(list1)
The list of children should only
consist of Node objects -- that is, all I need is their base class stuff. They shouldn't be fully realized into the specialized classes
(so I don't get the whole graph at once, among other reasons).
I started along the following lines, cobbling together bits and pieces I found in various places without a complete understanding of
what was going on, so this may not make much sense:
class ListNode(Node):
__mapper_args__ = {'polymorphic_identity': 'list', 'inherit_condition':id==Node.id}
__tablename__ = 'nodes_list_contents'
id = Column(None, ForeignKey('nodes.id'), primary_key=True)
item_id = Column(None, ForeignKey('nodes.id'), primary_key=True)
items = relation(Node, primaryjoin="Node.id==ListNode.item_id")
This approach fails in several ways: it doesn't appear to allow an empty ListNode, and setting the items attribute to a list results
in SQLAlchemy complaining that 'list' object has no attribute '_sa_instance_state'. Not surprisingly, hours of random mutations on this theme haven't given any
good results,
I have limited experience in SQLAlchemy but really want to get this working soon. I'd very much appreciate any advice or direction you can
offer. Thanks in advance!
You need an additional table for many-to-many relation:
nodes_list_nodes = Table(
'nodes_list_nodes', metadata,
Column('parent_id', None, ForeignKey('nodes_list.id'), nullable=False),
Column('child_id', None, ForeignKey(Node.id), nullable=False),
PrimaryKeyConstraint('parent_id', 'child_id'),
)
class ListNode(Node):
__mapper_args__ = {'polymorphic_identity': 'list'}
__tablename__ = 'nodes_list'
id = Column(None, ForeignKey('nodes.id'), primary_key=True)
items = relation(Node, secondary=nodes_list_nodes)
Update: below is an example for ordered list using association_proxy:
from sqlalchemy.orm.collections import InstrumentedList
from sqlalchemy.ext.associationproxy import association_proxy
class ListNodeAssociation(Base):
__tablename__ = 'nodes_list_nodes'
parent_id = Column(None, ForeignKey('nodes_list.id'), primary_key=True)
child_id = Column(None, ForeignKey(Node.id), primary_key=True)
order = Column(Integer, nullable=False, default=0)
child = relation(Node)
__table_args__ = (
PrimaryKeyConstraint('parent_id', 'child_id'),
{},
)
class OrderedList(InstrumentedList):
def append(self, item):
if self:
item.order = self[-1].order+1
else:
item.order = 1
InstrumentedList.append(self, item)
class ListNode(Node):
__mapper_args__ = {'polymorphic_identity': 'list'}
__tablename__ = 'nodes_list'
id = Column(None, ForeignKey('nodes.id'), primary_key=True)
_items = relation(ListNodeAssociation,
order_by=ListNodeAssociation.order,
collection_class=OrderedList,
cascade='all, delete-orphan')
items = association_proxy(
'_items', 'child',
creator=lambda item: ListNodeAssociation(child=item))