SQLAlchemy update if unique key exists

Question

I've got a class:

class Tag(Base, TimestampMixin):
    """Tags"""
    __tablename__ = 'tags'
    __table_args__ = {'mysql_engine' : 'InnoDB', 'mysql_charset' : 'utf8' }

    id = Column(Integer(11), autoincrement = True, primary_key = True)
    tag = Column(String(32), nullable = False, unique = True)
    cnt = Column(Integer(11), index = True, nullable = False, default = 1)

    def __init__(self, tag):
        t = session.query(Tag).filter_by(tag=tag).first()
        if t:
            self.cnt = t.cnt+1
            self.tag = t.tag
        else:
            self.tag = tag

    def __repr__(self):
        return "<Tag('%s')>" % (self.tag, )

    def __unicode__(self):
        return "%s" % (self.tag, )

When adding tag:

tag = Tag('tag')
session.add(tag)
session.commit()

I want it to update existing tag.

Of course, I could've done this:

tag = session.query(Tag).filter_by(tag='tag').first()
if tag:
    tag.cnt++
else:
    tag = Tag('tag')
session.add(tag)
session.commit()

but, keeping such logic in Tag class seems to be more clear - possibly keeps me off of the shotgun surgery.

How do I get there? I'm pretty new to Python and SQLAlchemy, so any additional thoughts on my code will be appreciated.

Thank you.

P.S. SQLAlchemy is SO GIGANTIC and they don't provide a handy way to do INSERT ... ON DUPLICATE KEY UPDATE, huh? WOW!

Solution 1

You can try this

def get_or_increase_tag(tag_name):
    tag = session.query(Tag).filter_by(tag=tag_name).first()
    if not tag:
       tag = Tag(tag_name)
    else:
       tag.cnt += 1
    return tag

You can check the link https://stackoverflow.com/search?q=Insert+on+duplicate+update+sqlalchemy

Solution 2

From version 1.2 SQLAlchemy will support on_duplicate_key_update for MySQL

There is also examples of how to use it:

from sqlalchemy.dialects.mysql import insert

insert_stmt = insert(my_table).values(
    id='some_existing_id',
    data='inserted value')

on_duplicate_key_stmt = insert_stmt.on_duplicate_key_update(
    data=insert_stmt.values.data,
    status='U'
)

conn.execute(on_duplicate_key_stmt)

---

From version 1.1 SQLAlchemy support on_conflict_do_update for PostgreSQL

Examples:

from sqlalchemy.dialects.postgresql import insert

insert_stmt = insert(my_table).values(
    id='some_existing_id',
    data='inserted value')

do_update_stmt = insert_stmt.on_conflict_do_update(
    constraint='pk_my_table',
    set_=dict(data='updated value')
)

conn.execute(do_update_stmt)

Comments

[Emil M]

try session.merge(tag) instead of session.add(tag)

[Hennadii Madan]

+100 on the P.S.

[willyhakim]

There should be a create_or_update function django orm style

[bl79]

typo: data=insert_stmt.values.data instead data=insert_stmt.inserted.data

[Ken]

How can you do this with session?