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Using SQLAlchemy-DataTables with Multiple Relationships Between the Same Tables


Using SQLAlchemy-DataTables with Multiple Relationships Between the Same Tables

By : Jack Liu
Date : October 17 2020, 01:08 AM
seems to work fine In order to join the same table multiple times you need aliases:
code :
In [9]: creator = db.aliased(User)

In [10]: last_modifier = db.aliased(User)
In [11]: columns = [
    ...:     ColumnDT(Post.id),
    ...:     ColumnDT(Post.subject),
    ...:     ColumnDT(creator.username),
    ...:     ColumnDT(last_modifier.username),
    ...:     ColumnDT(Post.modified_time)
    ...: ]
    ...: 
In [12]: query = db.session.query().\
    ...:     select_from(Post).\
    ...:     outerjoin(creator, Post.creator).\
    ...:     outerjoin(last_modifier, Post.last_modifier)


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SQLAlchemy relationships across multiple tables

SQLAlchemy relationships across multiple tables


By : Dacar Abdirisaq
Date : March 29 2020, 07:55 AM
this one helps. I'm trying to create a relationship that spans across 3 tables but I can't quite figure out the syntax.
SQLAlchemy Relationships between 3 tables

SQLAlchemy Relationships between 3 tables


By : Will Dai
Date : March 29 2020, 07:55 AM
around this issue This kind of query requires a join statement:
code :
q = session.query(Member).\
        join(Member.group).\
        join(Group.department).\
        filter(Department.name=='depart_name')

result = q.all()
SQLAlchemy Multiple relationships between tables

SQLAlchemy Multiple relationships between tables


By : jackpmccullough
Date : March 29 2020, 07:55 AM
it helps some times You've defined foreign_keys for the youngest_child relationship, but you also have to define it for the children and parent relationships:
code :
class Parent(Base):
    __tablename__ = 'parents'
    id = Column(Integer, primary_key=True)
    youngest_child_id = Column(Integer, ForeignKey('children.id'))
    youngest_child = relationship("Child", uselist=False, post_update=True,
                                  foreign_keys=[youngest_child_id])
    # Pass foreign_keys= as a Python executable string for lazy evaluation
    children = relationship("Child", back_populates='parent',
                            foreign_keys='[Child.parent_id]')

class Child(Base):
    __tablename__ = 'children'
    id = id = Column(Integer, primary_key=True)
    parent_id = Column(Integer, ForeignKey('parents.id'))
    parent = relationship("Parent", back_populates='children',
                          foreign_keys=[parent_id])
p = Parent()
c1, c2 = Child(), Child()
p.children = [c1, c2]
p.youngest_child = c1
session.add(p)
session.commit()
SQLAlchemy import tables with relationships

SQLAlchemy import tables with relationships


By : Habtamu Ayalew
Date : March 29 2020, 07:55 AM
To fix the issue you can do This should work (note that the TableC.table is replaced with the name of the table to avoid circular module loading):
Inserting relationships into a table which connects 3 tables with many to many relationships with SQLALchemy - python

Inserting relationships into a table which connects 3 tables with many to many relationships with SQLALchemy - python


By : Isidro A. López G.
Date : March 29 2020, 07:55 AM
like below fixes the issue You can always use an Association Object:
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