CODEWITHSUNDEEP
python-3.xpostgresqlsqlalchemy
JeyJ
JeyJ

Reputation: 4080

Python sqlalchemy - saving the many objects of one vs many

In my db I have one to many model (parent vs many children). Content of files :

class Parent(Base):
    __tablename__ = 'parent'
    id = Column('id', bigint, primary_key=True)
    name = Column('name', TEXT, nullable=False)
    lname = Column('lname', TEXT, nullable=False)
    register_date = Column('register_date',DateTime(timezone=True), default=datetime.datetime.utcnow)
    children = relationship('Child')

    def __init__(self, id, name,lname,register_date):
        self.id=id
        self.name=name
        self.lname=lname 

class Child(Base):
    __tablename__ = 'children'
    id = Column('id', bigint, primary_key=True)
    parent_id = Column('parents', ForeignKey('parents.id'), nullable=False)
    name = Column('name', TEXT, nullable=False)
    lname = Column('lname', TEXT, nullable=False)
    register_date = Column('register_date',DateTime(timezone=True), 
   
    parent = relationship('Parent', back_populates="children")

    def __init__(self, id, name, lname, parent):
        self.id=id
        self.name=name
        self.lname=lname 
        self.parent=parent

My input of the program is an XML file in the following format :

<Parent>
<name> fname_example </name>
<lname> lname_example </lname>
<id> id_example </id>
<Children>
<Child>
<name> fname_example </name>
<lname> lname_example </lname>
<id> id_example </id>
</Child>
<Child>
<name> fname_example </name>
<lname> lname_example </lname>
<id> id_example </id>
</Child>
</Children>
</Parent>

<Parent>
....
</Parent>

After parsing this XML file I have a list of parents and of children. At first, I'm saving the parents :

session.add_all(parents)

And after a few checks I'm also saving the children :

    session.bulk_save_objects(children)

My issue is that in this way the mapper doesn't map the parent to the children and in the insert query I see that null is mapped as the parent :

sqlalchemy.exc.InvalidRequestError: This Session's transaction has been rolled back due to a previous exception during flush. 
To begin a new transaction with this Session, first issue Session.rollback(). 
Original exception was: (psycopg2.errors.NotNullViolation) null value in column "parent" violates not-null constraint
DETAIL:  Failing row contains (1, null, 'Roger', 'Prince','01-10-2019')

Upvotes: 0

Views: 144

Answers (1)

JeyJ
JeyJ

Reputation: 4080

The solution in my case : I added the next row to the init method of the child ; self.parent_id=parent.id

Upvotes: 1

Related Questions