I have a comments table what is linked to blog post. For each comment in the database table it is listed as it's own row on the template. I would like to lazy load each comment so users browsers don't need to load thousands of comments in their browsers.
Is this what SQLAlchemy's lazy='dynamic' does? The docs confuse me on the subject of lazy and eager loading. I am only use to using lazy load libraries to lazily load images. I am new to Python, Flask and SQLAlchemy.
If per your comment, you're loading the comments via a query with yield_per, the lazy attribute is somewhat irrelevant as it applies to entity relationship mapping (e.g. if you were loading posts which each had their own comments mapped as a relationship attribute).
Unless you're planning to stream the comments over an HTTP connection that you will keep open, I'm not sure yield_per is the best choice.
An easiest solution would be to leverage http://flask-sqlalchemy.pocoo.org/2.1/api/#flask.ext.sqlalchemy.Pagination where you initially load the first page of comments, e.g. 25. Then upon a js scrolling event, kick an ajax call kicking the same query asking for page 2, and so on.
Hope it helps.
Related
What I have been trying to find, with no answer yet, is how I could have a user click on link to a template, then instead of waiting for the whole page to load, allow the user to view what has already loaded while they wait for more load heavy content to arrive, similar to what Facebook does when you first get to a page and see things loading.
There is not much more I can say as the question is pretty self-explanatory. I have checked google and stack overflow.
In order to allow the use to view the loaded page and dynamically view the rest of the page, you use a technology known as AJAX. It allows you to make asynchronous calls to the database, which can be triggered by some JS event(like onscroll) and load the queried data without reloading the entire page.
AJAX in Django is pretty straightforward, though some knowledge of JQuery(or even Javascript) will be required. You may also use the python package django-dajax which will make things easier. I think you will find the following links useful:
Tango with Django ajax guide (one of the best, but a bit tough)
django-dajax docs
Hope this helps!
My view function takes a long time until returning a template. So, I'd like to show something to a user while running the function.
Is it possible to show loader until a start page is loaded?
What's important is the loader should be shown when loading the first page after first visit of a user?
Thank you for reading my question.
You would have to fetch the page using JS. You could use something like Intercooler or PJAX which provides HTML attributes that show a spinning animation while loading the content via AJAX.
A better solution would be to make your page faster. There are several things you should consider:
Check that all Model fields that you are using for filtering or sorting have set db_index=True unless the tables are small (few hundred entries) or the fields are already unique or foreign/primary keys. Also check that your DB does sorting and merging in RAM not on disk (== the DB has enough RAM resources and has also the correct configuration to use it).
Sometimes, if you show a list of model instances you end up making separate DB requests per row if you access related models in your template. Again, check which statements your DB executes and have a look at Django's select_related, prefetch_related, values and values_list methods that can dramatically increase lookup performance. Make sure your template context contains all necessary data and only the necessary data (e.g. pageing, how much, or maybe you should consider a search index like SOLR or Elastic which can be integrated nicely via Django Haystack).
Load everything except heavy data at once in your main view, which also includes JS. The JS then uses AJAX to load the rest from a second Django view which returns an HTML snippet that your JS simply adds to the DOM.
It really depends on how comfortable you are with JS and how much you want to stick to HTML to make as much use of Django as possible (thinking of Django Forms for example). But first, tune your DB setup (disclaimer: I have written that article).
it's better to make a request with javascript to your Django endpoint, until you get a response back from your server you should show your loader, and when you get the response back successfully you should make display: none for loader and mak display: block for your loaded content
Create a function in views.py and send JsonResponse. URL example: http://localhost:8000/somedata
Render any other HTMLlet's say it's index.html. URL example: http://localhost:8000/home
That index.html file need to have some JavaScript, let's say main.js
In main.js make a request to http://localhost:8000/somedata and fetch data. Use async javascript that way you can easily track fetched data or not
I developed an application in JSPs and Servlets involving drop down menus that kept growing with how many authors per publication their were.
This was done in JavaScript and then in my application iterated through them using a loop. Is this possible using Django? This would be useful in my application.
This link might help you out if you don't want to dive into javascript (too much)
http://www.dajaxproject.com/
Or have a look at this stackoverflow question/awnser:
What is the best AJAX library for Django?
In any case, you need to serialize your array to a JSON string.
Then pass the JSON with an XMLHTTPRequest (ajax) to the server.
Add the javascript tag to your question if you don't mind more JS solutions.
Otherwise look for a Django Ajax framework to do the heavy lifting for you.
Plone has a beautiful search box with a "Google suggest" like functionality for its site. It even indexes uploaded documents like PDFs. Does anyone know of a module that can provide this kind of functionality in a Django site?
Plone implements it's LiveSearch feature by maintaining a separate metadata table of indexed attributes (fields such as last modified, creator, title are copied from the content objects into this table). Content objects then send ObjectAdded/ObjectModified/ObjectRemoved events, and an event subscriber listens for these events and is responsible for updating the metadata table (in Django events are named signals). Then there is a Browser View exposed at a fixed URL that searches the metadata and returns the appropriate LiveSearch HTML, and finally each HTML page is sent the appropriate JavaScript to handle the autocomplete AJAX functionality to query this view and slot the resulting HTML results into the DOM.
If you want your LiveSearch to query multiple Models/Content Types, you are likely going to need to send your own events and have a subscriber handle them appropriately. This isn't necessary for a smaller data sets or lower traffic sites, where the performance penalty for doing multiple queries for a single search isn't a concern (or you only want to search a single content type) and you can just do several queries from your View.
As for the JavaScript side, you can roll-your-own or use an existing JavaScript library. This is usually called autocomplete in the JS library. There is YUI autocomplete and Scriptaculous autocomplete for starters, and likely lots more JavaScript autocomplete implementations out there. Plone uses KSS for it's JavaScript library, the KSS livesearch plugin is a good place to start if looking for example code to pluck from.
http://pypi.python.org/pypi/kss.plugin.livesearch
And a tutorial on using KSS with Django:
http://kssproject.org/docs/tutorial/kss-in-django-with-kss-django-application
KSS is quite nice since it cleanly separates behaviour from content on the client side (without needing to write JavaScript), but Scriptaculous is conceptually a little simpler and has somewhat better documentation (http://github.com/madrobby/scriptaculous/wikis/ajax-autocompleter).
What would be the best way to port an existing Drupal site to a Django application?
I have around 500 pages (mostly books module) and around 50 blog posts. I'm not using any 3rd party modules.
I would like to keep the current URLS (for SEO purposes) and migrate database to Django. I will create a simple blog application, so migrating blog posts should be ok. What would be the best way to serve 500+ pages with Django? I would like to use Admin to edit/add new pages.
All Django development is similar, and yours will fit the pattern.
Define the Django model for your books and blog posts.
Unit test that model using Django's built-in testing capabilities.
Write some small utilities to load your legacy data into Django. At this point, you'll realize that your Django model isn't perfect. Good. Fix it. Fix the tests. Redo the loads.
Configure the default admin interface to your model. At this point, you'll spend time tweaking the admin interface. You'll realize your data model is wrong. Which is a good thing. Fix your model. Fix your tests. Fix your loads.
Now that your data is correct, you can create templates from your legacy pages.
Create URL mappings and view functions to populate the templates from the data model.
Take the time to get the data model right. It really matters, because everything else is very simple if your data model is solid.
It may be possible to write Django models which work with the legacy database (I've done this in the past; see docs on manage.py inspectdb).
However, I'd follow advice above and design a clean database using Django conventions, and then migrate the data over. I usually write migration scripts which write to the new database through Django and read the old one using the raw Python DB APIs (while it is possible to tie Django to multiple databases simultaneously, too).
I also suggest taking a look at the available blogging apps for Django. If the one included in Pinax suits your need, go ahead and use Pinax as a starting point.
S.Lott answer is still valid after years, I try to complete the analysis with the tools and format to do the job.
There are many Drupal export tools out of there by now but with the very same request I go for Views Datasource choosing JSON as format. This module is very solid and available for the last version of Drupal. The JSON format is very fast in both parsing and encoding and it's easy to read and very Python-friendly (import json).
Using Views Datasource you can create a node view sorted by node id (nid), show a limited number of elements per page, configure a view path, add to it a filter identifier and pass to it the nid to read all elements until you get an empty JSON response.
When importing in Django you have a wide set of tools as well, starting from loaddata to load fixtures. Views Datasource exported JSON but it's not formatted as Django expects fixtures: you can write a custom admin command to do the import, where you can have the full control of the import flow.
You can start your command passing a nid=0 as argument and then let the procedure read, import and then fetch data from the next page passing simply the last nid read in the previous HTTP request. You can even restrict access to the path on view but you need additional configuration on the import side.
Regarding performance, just for example I parsed and imported 15.000+ nodes in less than 10 minutes via a Django 1.8 custom admin command on an 8 core / 8 GB Linux virtual machine and PostgreSQL as DBMS, logging success and error information into a custom model for each node.
These are the basics for import/export between these two platform, for detailed information I described all the major steps for export from Drupal and then import to Django in this guide.