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Starter material for forms maintenance - online edit of handbook/troggle/trogforms.html - on dev machine 'Mohawk'

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Philip Sargent at home 2024-12-31 06:26:31 +00:00 committed by Philip Sargent
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<html><head><title>Handbook Troggle and HTML Forms</title></head><body>
<style>body { background: #fff url(/images/style/bg-system.png) repeat-x 0 0 }</style>
<h2 id="tophead">CUCC Expedition Handbook</h2>
<h1>Django and Troggle</h1>
<h1>Troggle and Django Forms</h1>
<h3>Django Versions and troggle</h3>
<h3>HTTP resquest/response</h3>
<p>OK the following assumes that you already have experience in creating and using HTML forms and that you know your way around HTTP requests (GET and POST) and HTTP responses (status + body). You may have used PHP, JSP or ASP for this in the past. If you haven't, then <a href="https://duckduckgo.com/?q=http+get+and+response&atb=v457-1&ia=web">start here</a>.
<h4>Django Forms History</h4>
<p>Django has several generations of quite different clever mechanisms to make creating HTML forms "easier". Yes, making them might be easier, but maintaining this opinionated stuff is a nightmare without adequately educating yourself how the architecture works. This will take time: do not hurry.
<p>WARNING: when reading the Django documentation on <a href="https://docs.djangoproject.com/en/5.1/topics/forms/">Forms</a> (unbound and <a href="https://docs.djangoproject.com/en/5.1/ref/forms/api/">bound</a>) and <a href="https://docs.djangoproject.com/en/dev/topics/forms/modelforms/">ModelForms</a>, do not get diverted into looking at Formsets or ModelFormsets. We do not use any formsets in troggle - of any kind.
<h4>Django Forms</h4>
<p>Just don't. Django has several generations of quite different clever mechanisms to make creating HTML forms "easier". Yes, making them might be easier, but maintaining this opinionated stuff is a nightmare. Really don't.
<hr />
<h3>Django 'Form' object</h3>
<ul>
<li>In <em>all</em> our data entry webpages we use a Django Form object to work with the response that the form sends back to the server, where we have to interpret the data and make an update to the database. The form is <em>bound</em> to the data that the user has provided.
<li>In <em>many</em> (but not all) we use a Django Form object in a Django template to render [some or all of the] the HTML which displays the input fields for the user. An empty form can be rendered to the user using an <em>unbound</em> form.
</ul>
<p>This is now a hint that you need to refresh your knowledge of <a href="https://docs.djangoproject.com/en/5.1/topics/templates/">the Django template system</a>. Fortunately you only need to know a tiny part of this to work with forms, basically just this idiom:
<code>{{ my_object.attribute }}</code>
and maybe also
<code>{{ my_dict.key }}</code>
<p>Now have a look at the Django templates for some of the forms you will already be familiar with from using them as a caver entering data, e.g. <a href="/logbookedit/2024-08-01c">Logbook entry editing</a> which uses the Django template <a href="/repositories/troggle/.git/tree/templates/logbookform.html">logbookform.html</a>...
<p>Hah, that was a nasty shock wasn't it? OK, most of that stuff is not the stuff which manages the data entry form. Concentrate on just the bits between the &lt;form&gt; ....&lt;/form&gt; tags.
<p>It might help you at this point to remind yourself how an ordinary webapge works, without a form. So look at <a href="/logbookentry/2024-08-01/2024-08-01c">a logbook entry</a> which just displays the data and the corresponding template <a href="/repositories/troggle/.git/tree/templates/logbookentry.html">logbookentry.html</a>.
<h4>HTML &lt;form&gt and fields</h4>
But if you haven't worked with HTML forms before, then you actually have <a href="https://developer.mozilla.org/en-US/docs/Web/HTML/Element/form">a whole lot of HTML</a> you will need to learn from scratch: how the <code>&lt;form&gt; ....&lt;/form&gt; </code> tag works, and how fields and labels and stuff works, and "input" and "textarea" and "submit".
<p>
You will also need to know about <a href="https://docs.djangoproject.com/en/5.1/ref/forms/widgets/">Django Widgets</a>.
<p>So that's enough to get you started. Now you are on your own, apart from help on the Website room of the Matrix chat and the nerd email list of course.
<h3>ModelForms</h3>
<p>A few of our data entry pages use <a href="https://docs.djangoproject.com/en/5.1/topics/forms/modelforms/">ModelForms</a>, these are where the Form object is automagically created from a Model class.
<hr />
Go on to: <a href="trogdjangup.html">Troggle: updating Django</a><br />
Return to: <a href="trogintro.html">Troggle intro</a><br />
Return to: <a href="trognotes.html">Troggle programmers' guide</a><br />
Troggle index:
<a href="trogindex.html">Index of all troggle documents</a><br />
<hr /></body></body></html>