SQLAlchemy ON DUPLICATE KEY UPDATE

I should mention that ever since the v1.2 release, the SQLAlchemy 'core' has a solution to the above with that's built in and can be seen under here (copied snippet below):

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.inserted.data,
    status='U'
)

conn.execute(on_duplicate_key_stmt)

My way

import typing
from datetime import datetime
from sqlalchemy.dialects import mysql

class MyRepository:

    def model(self):
        return MySqlAlchemyModel

    def upsert(self, data: typing.List[typing.Dict]):
        if not data:
            return
        model = self.model()
        if hasattr(model, 'created_at'):
            for item in data:
                item['created_at'] = datetime.now()

        stmt = mysql.insert(getattr(model, '__table__')).values(data)
        for_update = []
        for k, v in data[0].items():
            for_update.append(k)

        dup = {k: getattr(stmt.inserted, k) for k in for_update}
        stmt = stmt.on_duplicate_key_update(**dup)
        self.db.session.execute(stmt)
        self.db.session.commit()

Usage:

myrepo.upsert([
    {
        "field11": "value11",
        "field21": "value21",
        "field31": "value31",
    },
    {
        "field12": "value12",
        "field22": "value22",
        "field32": "value32",
    },
])

The other answers have this covered but figured I'd reference another good example for mysql I found in this gist. This also includes the use of LAST_INSERT_ID, which may be useful depending on your innodb auto increment settings and whether your table has a unique key. Lifting the code here for easy reference but please give the author a star if you find it useful.

from app import db
from sqlalchemy import func
from sqlalchemy.dialects.mysql import insert

def upsert(model, insert_dict):
    """model can be a db.Model or a table(), insert_dict should contain a primary or unique key."""
    inserted = insert(model).values(**insert_dict)
    upserted = inserted.on_duplicate_key_update(
        id=func.LAST_INSERT_ID(model.id), **{k: inserted.inserted[k]
                               for k, v in insert_dict.items()})
    res = db.engine.execute(upserted)
    return res.lastrowid