[FIXED] Why is Flask-SQLAlchemy object only being rendered when I am using pagination? (Jinja2)

Issue

I am new to web development and can't figure out why the data from my SQLite database isn't being rendered unless I include lines of code that cause it to be paginated.

Code without pagination:

@tools.route("/toolkit/feedback/user/<string:username>", methods=['GET', 'POST'])
@login_required
def feedback(username):
    user = User.query.filter_by(username=username).first_or_404()
    feedback = Feedback.query.filter_by(author=user).all()
    return render_template("comments.html", feedback=feedback, user=user)

Code with pagination:

@tools.route("/toolkit/feedback/user/<string:username>", methods=['GET', 'POST'])
@login_required
def feedback(username):
    page = request.args.get('page', 1, type=int)
    user = User.query.filter_by(username=username).first_or_404()
    feedback = Feedback.query.filter_by(author=user)\
            .paginate(page=page, per_page=10)
    return render_template("comments.html", feedback=feedback, user=user)

HTML/Jinja2:

{% extends 'layout.html' %}
{% block content %}
<ul class="list-group list-group-flush">
    {% for teacher_feedback in feedback.items %}
    <li class="list-group-item">{{ teacher_feedback.comment }}</li>
  {% endfor %}
</ul>


    {% for page_num in feedback.iter_pages(left_edge=1, right_edge=1, left_current=1, right_current=2) %}
    {% if page_num %}
      {% if feedback.page == page_num %}
        <a class="btn btn-info mb-4" href="{{ url_for('tools.feedback', username=user.username, page=page_num) }}">{{ page_num }}</a>
      {% else %}
        <a class="btn btn-outline-info mb-4" href="{{ url_for('tools.feedback', username=user.username, page=page_num) }}">{{ page_num }}</a>
      {% endif %}
    {% else %}
      ...
    {% endif %}
  {% endfor %}
{% endblock content %}

Solution

The paginate function returns a Pagination object which has the iter_pages method. A standard SQLAlchemy query doesn't have this method which is why you don't see anything when you try iterate over feedback in your template.

As this line feedback = Feedback.query.filter_by(author=user).all() gives you a list, in the HTML for you non-paginate method you could try as a test:

{% for f in feedback %}
    <p>{{f.AN_ATTRIBUTE_OF_FEEDBACK}}</p>
{% endfor %}

Answered By - PGHE