How to do an upsert with SqlAlchemy?

Question

I have a record that I want to exist in the database if it is not there, and if it is there already (primary key exists) I want the fields to be updated to the current state

Answer 1

This allows access to the underlying models based on string names

def get_class_by_tablename(tablename):
  """Return class reference mapped to table.
  https://stackoverflow.com/questions/11668355/sqlalchemy-get-model-from-table-name-this-may-imply-appending-some-function-to
  :param tablename: String with name of table.
  :return: Class reference or None.
  """
  for c in Base._decl_class_registry.values():
    if hasattr(c, '__tablename__') and c.__tablename__ == tablename:
      return c


sqla_tbl = get_class_by_tablename(table_name)

def handle_upsert(record_dict, table):
    """
    handles updates when there are primary key conflicts

    """
    try:
        self.active_session().add(table(**record_dict))
    except:
        # Here we'll assume the error is caused by an integrity error
        # We do this because the error classes are passed from the
        # underlying package (pyodbc / sqllite) SQLAlchemy doesn't mask
        # them with it's own code - this should be updated to have
        # explicit error handling for each new db engine

        # add explicit error handling for each db engine 
        active_session.rollback()
        # Query for conflic class, use update method to change values based on dict
        c_tbl_primary_keys = [i.name for i in table.__table__.primary_key] # List of primary key col names
        c_tbl_cols = dict(sqla_tbl.__table__.columns) # String:Col Object crosswalk

        c_query_dict = {k:record_dict[k] for k in c_tbl_primary_keys if k in record_dict} # sub-dict from data of primary key:values
        c_oo_query_dict = {c_tbl_cols[k]:v for (k,v) in c_query_dict.items()} # col-object:query value for primary key cols

        c_target_record = session.query(sqla_tbl).filter(*[k==v for (k,v) in oo_query_dict.items()]).first()

        # apply new data values to the existing record
        for k, v in record_dict.items()
            setattr(c_target_record, k, v)