sqlalchemy_upsert.py

from sqlalchemy.dialects import postgresql

def upsert(session, model, fields, returning=False, return_columns=None):
    table = model.__table__

    stmt = postgresql.insert(table).values(**fields)

    pk_columns = table.primary_key.columns.keys()
    update_cols = {col: val for col, val in fields.items() if col not in pk_columns}

    if update_cols:
        stmt = stmt.on_conflict_do_update(
            constraint=table.primary_key,
            set_=update_cols,
        )
    else:
        stmt = stmt.on_conflict_do_nothing()

    if returning:
        if not return_columns:
            return_columns = table.columns

        stmt = stmt.returning(*return_columns)

    result = session.execute(stmt)

    if returning:
        return model(**result.fetchone())

    return None