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python-2.7jinja2flask-sqlalchemy

Length of list in jinja template, where the list is the result of a DBSession.query

How do I find the length of a list of objects in a jinja template when the list of objects has been created by querying a database?

I thought There are {{ items|length }} items in this category. would work, but items is a result of:

items = db_session.query(Item).filter_by(category_id=category.id)

and I get the error

TypeError: object of type 'Query' has no len()

Obviously, I could calculate the length separately and pass into render_template(), but I wondered if there was a better way?

Any help from the community would be much appreciated :)

Solution

  • items object is not a list yet, it is an unprocessed Query object as you see in the error. You can use Query.all() method to get a list of items:

    items = db_session.query(Item).filter_by(category_id=category.id).all()

    After that length filter can be applicable.