Adding indexes to SQLAlchemy models after table creation

Question

I have a flask-sqlalchemy model:

class MyModel(db.Model):
__tablename__ = \'targets\'
id = db.Column(db.Integer, primary_key=True)
url = db.Column(db.String(2048         


        

Answer 1

I am not sure if this conforms to best practices but I found Alembic would notify me of Indexes in the __table_args__ but not actually make them for me during migrations. I made this small script that can generate new indexes found in the __table_args__ property. It makes use of Index.create() as mentioned above, but will generate new indexes if they do not exist.

def create_indexes(db, drop_index=False):
    """
    Creates all indexes on models in project if they do not exists already. Assumes all models
    inherit from RequiredFields class, otherwise will need to adjust search for subclasses. If the index
    exists SQLAlchemy throws an error and we assume everything is ok. 
    :param db: The app db object, acts as the engine param for the Index.create()
    :param drop_index: specifies whether the indexes should be dropped or created
    :return:
    """
    from application.base_models import RequiredFields
    from sqlalchemy import Index
    from sqlalchemy.exc import ProgrammingError
    for klass in RequiredFields.__subclasses__():
        if hasattr(klass, '__table_args__'):
            for item in getattr(klass, '__table_args__'):
                if isinstance(item, Index):
                    try:
                        if not drop_index:
                            item.create(db.engine)
                        else:
                            item.drop(db.engine)
                    except ProgrammingError:  # If index exists, creation fails on error
                        pass
    return

Here is a sample class showing the indexes.

class MyModel(RequiredFields):

    __table_args__ = (
         db.Index( ... ),
         db.Index( ... ),
    )