python,google-app-engine,flask , Flask Python - Pull information from google datastore and display on own url


Flask Python - Pull information from google datastore and display on own url

Question:

Tag: python,google-app-engine,flask

This is my flask applicaion running on google app engine, the code below is a bit of my views.py file. All I'm trying to do is display the stored database information on it's own page with the URL being the ID. The top route works, but the bottom doesn't.

@app.route('/')
def list_posts():
    posts = Post.all()
    return render_template('list_posts.html', posts=posts)

@app.route('/posts/<int:id>')
def display_posts(id):
    posts = Post.all()
    return render_template('display_posts.html', posts=posts)

And this is my template:

{% extends "base.html" %}

{% block content %}
<ul>
    <h1 id="">Posts registered on the database</h1>
    <li>
        {{ post.title }} (written by {{ post.author.nickname() }})<br />
        {{ post.content }}
    </li>
</ul>
{% endblock %}

This is the error I get:

<class 'jinja2.exceptions.UndefinedError'>: 'post' is undefined
Traceback (most recent call last):
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/main.py", line 4, in <module>
    run_wsgi_app(app)
  File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/webapp/util.py", line 99, in run_wsgi_app
    run_bare_wsgi_app(add_wsgi_middleware(application))
  File "/base/data/home/runtimes/python/python_lib/versions/1/google/appengine/ext/webapp/util.py", line 117, in run_bare_wsgi_app
    result = application(env, _start_response)
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/flask/app.py", line 874, in __call__
    return self.wsgi_app(environ, start_response)
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/flask/app.py", line 864, in wsgi_app
    response = self.make_response(self.handle_exception(e))
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/flask/app.py", line 861, in wsgi_app
    rv = self.dispatch_request()
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/flask/app.py", line 696, in dispatch_request
    return self.view_functions[rule.endpoint](**req.view_args)
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/blog/views.py", line 26, in display_posts
    return render_template('display_posts.html', posts=posts)
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/flask/templating.py", line 81, in render_template
    context, ctx.app)
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/flask/templating.py", line 65, in _render
    rv = template.render(context)
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/jinja2/environment.py", line 891, in render
    return self.environment.handle_exception(exc_info, True)
  File "/base/data/home/apps/s~smart-cove-95709/1.384716942984350887/blog/templates/display_posts.html", line 1, in <module>
    {% extends "base.html" %}

Answer:

Both your render_template calls only pass a posts object:

# in list_posts:
return render_template('list_posts.html', posts=posts)
# in display_posts:
return render_template('display_posts.html', posts=posts)

Your template however only refers to a singular post:

{{ post.title }} (written by {{ post.author.nickname() }})<br />
{{ post.content }}

So when jinja tries to render the template, it tries to fill in the placeholders using what’s stored in the variable post, but there is none.

So for this template to work, you would have to pass a single post to the template, e.g.:

return render_template('list_posts.html', post=single_post)

However, the way you have written your template, it makes more sense that you intended to show multiple posts in a list. So in that case, you should pass a list of posts as posts—as you do right now—but change the template to iterate over that list and generate the output for each single post in that list instead:

{% block content %}
<ul>
    <h1 id="">Posts registered on the database</h1>
    {% for post in posts %}
    <li>
        {{ post.title }} (written by {{ post.author.nickname() }})<br />
        {{ post.content }}
    </li>
    {% endfor %}
</ul>
{% endblock %}

The /posts/<id> route should probably work like this:

@app.route('/posts/<int:id>')
def display_post(id):
    q = Post.all()
    post = q.filter('id =', id)
    return render_template('display_post.html', post=post)

Note that we only pass a single post, so the template should only expect a single post. You should always try to make it clear whether you are talking about a single or multiple objects by using singular or plural in your variable names, your method names, and your template names (E.g. display_post, display_post.html, and post versus list_posts, list_posts.html, and posts).


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