On Tuesday, 15 May 2018 12:21:26 UTC+1, Anton Smirnov wrote:
>
> I have two models: "Sensors" with information about its and "Measurments" .
>
> class Sensor(models.Model):
> date_start = models.DateField()
> Latitude = models.DecimalField(max_digits=18, decimal_places=15)
> Longitude = models.DecimalField(max_digits=18, decimal_places=15)
>
> def __str__(self):
> return 'id:%s / %s' % (self.id, self.date_start)
> class Measurment(models.Model):
> sens = models.ForeignKey(Sensor, on_delete=models.PROTECT)
> time_of_measurment = models.DateTimeField()
> humidity = models.PositiveSmallIntegerField()
> temperature1 = models.DecimalField(max_digits=5, decimal_places=2)
> temperature2 = models.DecimalField(max_digits=5, decimal_places=2)
> temperature3 = models.DecimalField(max_digits=5, decimal_places=2)
>
> def __str__(self):
> return 'sens_id:%s, time:%s' % (self.sens.id, self.time_of_measurment)
>
> From each sensor I serially recive measurments. On the page, it is
> necessary to display the sensor data and the one latest measurement data
> from the "Measurments" model corresponding for each sensor.
>
> for displaying sensors data I used ListView:
>
> view:
>
> from .models import Sensor, Measurmentclass SenorsListView(generic.ListView):
> model = Sensor, Measurment
> context_object_name = 'sensors_list'
> template_name = 'sensors_list.html'
> queryset = Sensor.objects.all().order_by('-date_start')
>
> template "sensors_list.html":
>
> {% extends "base_generic.html" %}{% block content %}
> <h1>Sensors List</h1>
> {% if sensors_list %}
> <table class="table">
> <tr>
> <td><h4>ID sens<h4></td>
> <td><h4>Date of install<h4></td>
> <td><h4>Latitude<h4></td>
> <td><h4>Longitude<h4></td>
> <td><h4>Data from last measurments<h4></td>
> </tr>
> {% for sensor in sensors_list %}
> <tr>
> <td>{{sensor.id}}</td>
> <td>{{sensor.date_start}}</td>
> <td>{{sensor.Latitude}}</td>
> <td>{{sensor.Longitude}}</td>
> <td>{{}}</td>
> </tr>
> {% endfor %}
> </table>
> {% else %}
> <p>There are no sensors in the DB.</p>
> {% endif %} {% endblock %}
>
> But dont know How to display data about last measurments. I think need
> using aggregate to calculate last_time how Max(time_of_measurment) for each
> id_sens. And then get it whith filter(sens=id_sens, time_of_measurment =
> last_time )
>
> How it can be done right?
>
An easy way to do this would be to define the default ordering for
Measurment to be by reverse time; then you can access
`sensor.measurment_set.first` directly in the template.
class Measurment:
...
class Meta:
ordering = ['-time_of_measurment']
...
{% for sensor in sensors_list %}
...
{% with sensor.measurment_set.first as last_measurment %}
{{ last_measurment.humidity }} # etc
{% endwith %}
{% endfor %}
--
DR.
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