Django: AJAX code needed for dependent dropdowns - javascript

Since I'm new to Django and have absolutely no knowledge of JS/AJAX, I'm trying to code in the most simple possible way dependent dropdowns. I managed to get my dropdowns populated with values from my database (data_immo). Now I need to have the second dropdown updated after user selection in the first one.
Here is my home.html file with the two dropdowns (regions and departements):
<select name="regions" id="regions">
{% for item in query_results_dict %}
<option value={{ item.nom_reg }}>{{ item.nom_reg }}</option>
{% endfor %}
</select>
<select name="departements" id="departements">
{% for item in departements %}
<option val="{{ item.insee_dep }}"> {{ item.insee_dep }} </option>
{% endfor %}
</select>
views.py:
def MyView(request):
query_results = data_immo.objects.all()
regions = data_immo.objects.values_list("nom_reg", flat=True).distinct()
departements = data_immo.objects.values_list("insee_dep", flat=True).distinct()
query_results_dict = {
'query_results': query_results,
'regions': regions,
'departements': departements,
}
return render(request,'home.html', query_results_dict)
models.py:
class data_immo(models.Model):
id = models.AutoField(primary_key=True)
insee_dep = models.IntegerField(db_column='INSEE_DEP', blank=True, null=True)
nom_reg = models.TextField(db_column='NOM_REG', blank=True, null=True)
class Meta:
managed = True
db_table = 'immo'
My understanding is that I need to retrieve the selected value from the "regions" dropdown and use an onChange function to trigger an action that will use that variable and inspect the db so only matching depatements are selected. Unfortunately I don't know how to proceed. I know there are a few examples out there, but none of them were really satisfying, and those I tried failed due to my lack of JS/AJAX knowledge.
Let me know if need more details.
EDIT 1: added models.py; also, the website that has been recommended in the comments has values stored in different tables whereas mine are all in the same one. Surely this must have an impact on my code and cannot be replicated per se.

Related

How to deal with dependable dropdowns in Django

I am trying to create a dependable dropdown on Django but since my JavaScript/ajax knowledge is not great, I have hit rock bottom. Note: I have read previous questions on this matter but none of them fully solved my problem.
Problem Description:
Due to my database size, I am retrieving partial data from the server whenever a view is requested. This makes my job of using forms harder since I am using the username of the user to filter my server. Here is a simplified version of my code.
urls.py
urlpatterns = [
url(r'^SpecificVessel', views.SpecificVessel, name="goSpecificVessel"),
]
views.py
#login_required
def SpecificVessel(request):
#Get the username to filter the tables from SQL Server:
username = None
if request.user.is_authenticated:
username = request.user.username
#Get the shipnames.
cursor.execute("select distinct SHIPNAME from Table where [GROUP]=" + "'" + username + "'")
row = cursor.fetchall()
df_listofships = pd.DataFrame(data=row, columns=['SHIPNAME'])
shipnames = list(df_listofships['SHIPNAME'].tolist()) # LIST FOR SHIP SELECTION
#Get All the data from database.
cursor.execute("select * from Table2 where [GROUP]=" + "'" + username + "'")
row = cursor.fetchall()
df = pd.DataFrame(data=row)
colnames = list(dftrans.columns.values.tolist()) #LIST FOR YEAR DROPDOWN SELECTION
#getting the dropdown selections:
Dropdown_shipname = request.POST.get('Dropdown_shipname')
Dropdown = request.POST.getlist('Dropdown')
return render(request, 'SpecificVessel.html',
{'colnames': colnames, 'Dropdown': Dropdown, 'shipnames': shipnames, 'Dropdown_shipname': Dropdown_shipname,})
SpecificVessel.html
<form method="post">
{% csrf_token %}
<div class="form-group col-md-4">
<label for="Dropdown_shipname"><b>Select Vessel</b></label>
<select name="Dropdown_shipname" id="Dropdown_shipname" data-style="btn-default" class="selectpicker form-control" >
{% for i in shipnames %}
<option value="{{ i }}" {% if Dropdown_shipname == i %} selected {% endif %}>{{ i }} </option>
{% endfor %}
</select>
</div>
<div class="form-group col-md-4">
<label for="Dropdown"><b> Select Month </b></label>
<select name="Dropdown" id="Dropdown" data-style="btn-default" class="selectpicker form-control" multiple>
{% for i in colnames %}
<option value="{{ i }}" {% if Dropdown == i %} selected {% endif %} >{{ i }} </option>
{% endfor %}
</select>
</div>
<div class="form-group col-md-1 margin_top_25">
<input type="submit" value="Submit" />
</div>
</form>
What is the problem?
The solution I have in the code above provides me with independent dropdowns. That is, whenever there is a mismatch, it throws me an error. I have been trying to approach this in different way, however, after long research online, I found out that javascript or ajax may be the way to go about this. My question is this: Is there any way in which I could get what the user has selected in Dropdown_shipname before he submits the results? If yes, how would you solve this problem?
I hope I was clear enough. Please let me know if I should explain the problem any better.
There's a lot I feel I need to address before answering your main question.
The if request.user.is_authenticated bit is unnecessary; you already decorate the view with #login_required, so there's no way the user isn't authenticated.
Where does cursor come from? It doesn't look like you're using Django's database stuff (the ORM, or even raw cursors), but something else? Why is that?
Having a global cursor may lead to trouble down the line in production, when it's being shared between requests in a multithreaded situation. (Using Django's database functionality the database connections are correctly reset between requests, and each thread gets its own connection.)
Your SQL queries are vulnerable to SQL injection attacks, since you're just concatenating strings together. You need to use placeholders (parametrized queries) instead. How that's done depends on the database and database driver you're using.
You definitely don't need Pandas and a Pandas dataframe to extract the data from your database result! (My pet peeve: useless use of Pandas.)
The first retrieval would be shipnames = [row[0] for row in cursor].
The second retrieval would be colnames = [d[0] for d in cursor.description] (or similar; depends on your database). (However, you really don't want to fetch a number of rows just to get the column names; one row, e.g. LIMIT 1 in standard SQL, would do.)
You should be using Django forms to manage, well, forms. That way you don't need to manage rendering the <select>s and <option>s and selecteds manually.
This view would likely become a FormView subclass.
You say "This makes my job of using forms harder since I am using the username of the user to filter my server.", but that's a non-issue. You can well pass in your Django request, or just the User, or an username, to a custom form class, and have it modify or even add fields dynamically to the form based on it.
That said, the most minimal solution here is a tiny bit of JavaScript, to refresh the page with an added query string argument for the first selection. That is, when the user changes the shipname field, you'd refresh the page with e.g. ?shipname=selection-here, and deal with figuring out the correct choices for the other field in your view code.
The most minimal way I can think of is
<script>
document.getElementById("Dropdown_shipname").addEventListener("change", (event) => {
location.href = `?shipname=${event.target.value}`;
}, false);
</script>
Beyond that, you could use an AJAX request to selectively refresh only part of the page, and beyond that, maybe refactor the form into, say, a React.js or Vue.js component that deals with the form.
But either way, no, you're not going to be able to dynamically change the other field without JavaScript.

Is there an alternative for onload on <select>?

I am using jinja templates to compile a form of multiple select blocks based on a template variable dictionary, like this:
{% for key, value in some_template_variable_dict.items %}
<select id="{{ key }}_selector" name="key">
{% for item in values %}
<option value="{{ item }}">{{ item }}</option>
{% endfor %}
</select>
{% endfor %}
I would like to fire the following wrapper function for selectize on all of the select blocks on loading the document:
function selectizeSingleChoice(selector) {
$('#'+selector).selectize({
sortField: 'text',
maxItems: 1,
create: false,
highlight: true,
openOnFocus: true
});
}
The select block does not have an onload event handler, and I cannot put it in a general $(document).ready(); section either, as the exact list of select blocks and their id-s is dependent on user choice. There is also an option that a slightly different version of the selectize wrapper is needed for some of them (e.g. not only one selected option allowed etc), so I cannot fire it on each and every select item either.
A working solution is to insert a script tag inside the for loop, but I dislike it for being messy.
Since your data is generated dynamically you could mark each select option with a class that specifies it's type like class="type1" and class="type2" so later you can do separate actions on them from the JS side. Or you could use the HTML data-* attribute to differentiate them.

Keep option selected on page refresh

So how my code works i'll give you a gist.
When there are no files in html_files, the default option is "---", but when there exists a file in html_files there are two options now,
1) "---"
2) file. But with default still as "---"
So what i want to do is, when there exists a file in html_files I want the default option change to the current file and not "---". I cant think of a way as to how to do it. Could someone help me?
<span title="list resources who's involved etc">About File:
<select class="experiment_file_selector" id="about_file" name="about_file">
<option value="None" {% if not exp.about_file %}selected="selected"{% endif %}>---</option>
{% for file in html_files %}
<option value="{{ file.id }}" {% if file == exp.about_file %}selected="selected"{% endif %} >{{ file.get_base_name }}</option>
{% endfor %}
</select></span>
I added a JS script as suggested below it does the work on getting the default file on the select input tag when the exp.about_file is present but for it to get displayed on the template it needs to be manually clicked.
To automate the process i tried using .click() which seems to fail somehow.
So basically how its working, of i select the first option from the select list "---" or listFile[0] and then select the second one exp.about_file or listFile[1] manually, it delivers the result some how but its not happening with the JS script.
So could someone suggest me a method to automate the mouse click event for
listFile[0] and listFile[1], somewhat like my JS code so that it works.
Thanks
$(document).ready(function(){
var listFile = document.getElementById('about_file');
if (listFile.length > 1)
{
listFile[1].setAttribute('selected', 'selected');
listFile[0].click();
listFile[1].click();
}
});
It will be easy if you use javascript. Just add attribute selected="selected" when your page loaded.
document.addEventListener('DOMContentLoaded', function(e) {
var listFile = document.getElementById('about_file');
if (listFile.length > 1) {
listFile[1].setAttribute('selected', 'selected');
}
});

Flask: remembering variables + DOM manipulation throughout application

I'm developing a Flask application that contains a ton of inputs. Some the inputs depend on other inputs so there is some DOM manipulation to expose these dependent inputs. I would like for the application to remember the DOM state when the user goes back so the user doesn't have to reenter everything. What's the best way to do this?
Below demonstrates what I think should work. I have an input box that takes a number. There is also a button that adds the same input field to the DOM. When the user clicks submit, these inputs are appended to input_list and the list is displayed on the UI. Because input_list is a global variable, the application will remember these inputs and their values (even if I go back in the browser or reload the page) - this is what I'm looking for.
Again, I'm not sure if this is the best way to do it. I know flask.g can be used to store application globals but I'm not sure this is the right use case for that (I've only seen that used to store database connections). I've also heard cookies may be useful for remembering changes in the DOM. Any thoughts/examples would be helpful and if anyone thinks my way is okay, I'd appreciate feedback on my code below.
app.py:
#app.route('/input_page', methods=['GET', 'POST'])
def input_page():
global input_list
input_list = []
if request.method == 'POST':
if request.form.get('empty_list'):
input_list = []
elif request.form.get('submit_list'):
input_list = [int(i) for i in request.form.getlist('x')]
return render_template('input_page.html', input_list=input_list)
input_page.html:
<p>{{ input_list }}</p>
<form method="POST" action="/input_page">
<div id="input_container">
{% if input_list %}
{% for i in input_list %}
<input type="number" name="x" value="{{ input_list[loop.index0] }}">
{% endfor %}
{% else %}
<input type="number" name="x">
{% endif %}
</div>
<button type="button" id="add_input">Add Input</button>
<input type="submit" value="Submit List" name="submit_list">
<input type="submit" value="Empty List" name="empty_list">
</form>
<script>
$(document).ready(function(){
$('#add_input').click(function(){
var $new_input = $('<input>', {type: 'number', name: 'x'});
$('#input_container').append($new_input);
});
})
</script>
You seem to be on the right track. However, I would shy away from a global variable because that essentially exposes the variable to other concurrent clients. I would however, recommend using the Flask session object:
from flask import Flask, session, ... # other flask modules you already have imported
Then in your Python code, you'd use:
def input_page():
if request.method == 'POST':
if request.form.get('empty_list'):
session['input_list'] = []
elif request.form.get('submit_list'):
session['input_list'] = [int(i) for i in request.form.getlist('x')]
input_list = session.get('input_list', False) # create an input_list var that either grabs the 'input_list' object from the session object or defaults to False if no key found
return render_template('input_page.html', input_list=input_list)

Javascript validation for dynamically generated forms in Django template

I am struggling with something that is probably very basic: I need to generate a form with marks for my University database application. Each student in each module has a class got "Performance" that stores all the marks for the module. There are different assessments and the Performance class calculates the average for them.
I need to be able to enter, for example, all the marks for the first assessment, and I did that with a dynamically generated Django Form as a table in the template:
{% for performance in performances %}
<tr>
<td>
{{ performance.student }}
</td>
<td>
{% if to_mark == 1 %}
<input type="text" class="input-mini" name="{{ student.student_id }}" value="{{ performance.assessment_1 }}">
{% else %}
{{ performance.assessment_1 }}
{% endif %}
</td>
And the same for the other assessments (to_mark gets passed on by views.py to indicate which assessments needs to be marked here)
I have failed to use Inlineformfields and therefore decided to generate a form dynamically and validate it with Javascript, also because the validation is simple (has to be a number between 1 and 100), and also because I want to use Javascript to calculate the average on the fly.
My problem is that I have no clue about Javascript. All the tutorials (like this one http://www.w3schools.com/js/js_form_validation.asp) use the name of the form field in the Javascript function, but in my case that name is dynamically generated, so that I can access it easily in the views.py:
if student.student_id in request.POST:
tmp = request.POST[student.student_id]
try:
mark = int(tmp)
if mark in range(0, 100):
performance = Performance.objects.get(student=student, module=module)
if to_change == 1:
performance.assessment_1 = mark
...and so on for the other assessments
except ValueError:
pass (in case someone accidentally enters a letter and not a number)
Is there a way I can use Javascript to address my form fields? Or should I use a different approach than taking the student_id as the name to read it out? How could I do that?
Thanks,
Tobi
There are at least 3 ways to get to the form fields using JavaScript:
By ID, by CSS class or by DOM traversal. If you're not familiar with JavaScript, I would suggest finding a django-friendly client-side form validator like: https://code.google.com/p/django-ajax-forms/

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