complex math calculation from query set

[mab.mo...@gmail.com]

Hello,

I am trying to perform a complex math calculation from a django query set. How can I pass the results to the template for display? Annotations won't work since the math is not a simple sum, diff or average. 

MODEL

class TncData(models.Model):

    callsign = models.TextField(max_length=20)

    lat = models.FloatField(null=True, blank=True, default=None)

    lon = models.FloatField(null=True, blank=True, default=None)

    path = models.TextField(max_length=250)

    message = models.TextField(max_length=250)

    dt_heard = models.DateTimeField(auto_now_add=False)

    def __str__(self):

        return str(self.callsign)

VIEW

def position_view(request):

    packet_data = TncData.objects.exclude(lat=0).order_by('-dt_heard')[:100]

    # my complex math calculation

     # need to do something like append distance to packet_data like packet_data.distance

    distance = "# complex math formula using packet_data.lat and packet_data.lon"

    return render(request, 'main/position.html', {'packet_data':packet_data,})

TEMPLATE

{% for field in packet_data %}

    <tr class='atable'>

    <td class='atable'>{{field.callsign}}</td>

    <td class='atable'>{{field.lat|floatformat:2}} N {{field.lon|floatformat:2}} W </td>

    <td class='atable'></td>

    <td class='atable'>{{packet_data.distance}}</td>

    <td class='atable'>{{field.dt_heard|date:"D m/d H:i"}}</td>

    </tr>

{% endfor %}

                         

[Derek]

See:  https://stackoverflow.com/questions/54412377/adding-values-to-django-queryset 

VIEW

def position_view(request):

    packet_data = TncData.objects.exclude(lat=0).order_by('-dt_heard')[:100]

    for packet in packet_data:

        # my complex math calculation

        packet.distance = "# complex math formula using packet.lat and packet.lon"

    return render(

        request, 

        'main/position.html',

        {'packet_data': packet_data, 'distance': distance})

TEMPLATE

# suggest you use a better term than "field" => maybe "record"?

{% for field in packet_data %}

    <tr class='atable'>

    <td class='atable'>{{field.callsign}}</td>

    <td class='atable'>{{field.lat|floatformat:2}} N {{field.lon|floatformat:2}} W </td>

    <td class='atable'></td>

    <td class='atable'>{{field.distance}}</td>

HTH!

[Derek]

Ignore the "'distance': distance" in the return - that should not be there.

[mab.mo...@gmail.com]

Thanks Derek. I'll give it a try

[mab.mo...@gmail.com]

Thank you Derek for the information. For those that are having similar problems this is the solution that worked for me based on Derek's lead....

## METHOD 1 ##

# view

def position_view(request):

    packet_data = TncData.objects.exclude(lat=0).order_by('-dt_heard')[:100]

    # loop through query set and add new dictionary key-value pair

    for row in packet_data:

        

        row.distance = row.lat*row.lon # example only of calculation  only not real 

    return render(request, 'main/position.html', {'packet_data':packet_data,})

# html template snippet

{% for row in packet_data %}

    <tr class='atable'>

    <td class='atable'>{{row.callsign}}</td>

    <td class='atable'>{{row.lat|floatformat:2}} N {{row.lon|floatformat:2}} W </td>

    <td class='atable' style='text-align:right;'>{{row.distance|floatformat:1}} miles</td>

    <td class='atable' style='text-align:right;'>{{row.bearing|floatformat:0}} deg</td>

    <td class='atable' style='padding-left:20px;'>{{row.dt_heard|date:"D m/d H:i"}}</td>

    </tr>

{% endfor %}

## METHOD 2 use @property in the model.py file 

# Put the data calculations in the model.py file

class TncData(models.Model):

    callsign = models.TextField(max_length=20)

    lat = models.FloatField(null=True, blank=True, default=None)

    lon = models.FloatField(null=True, blank=True, default=None)

    path = models.TextField(max_length=250)

    message = models.TextField(max_length=250)

    dt_heard = models.DateTimeField(auto_now_add=False)

    def __str__(self):

        return str(self.callsign)

    ## HAVERSINE FORMULA

    @property

    def calculate_distance(self):

        # Variables

        r = 6371 # radius earth km

        lat_1 = radians(42.97)

        lon_1 = radians(89.77)

        lat_2 = radians(self.lat)

        lon_2 = radians(self.lon)

        dlat = lat_1 - lat_2

        dlon = lon_1 - lon_2

        a = sin(dlat / 2)**2 + cos(lat_1) * cos(lat_2) * sin(dlon / 2)**2

        c = 2 * asin(sqrt(a))

        distance_km = c*r

        distance = distance_km * 0.621

        return(distance)

# html template snippet

{% for row in packet_data %}

    <tr class='atable'>

    <td class='atable'>{{row.callsign}}</td>

    <td class='atable'>{{row.lat|floatformat:2}} N {{row.lon|floatformat:2}} W </td>

    <td class='atable' style='text-align:right;'>{{row.calculate_distance|floatformat:1}} miles</td>

    <td class='atable' style='text-align:right;'>{{row.bearing|floatformat:0}} deg</td>

    <td class='atable' style='padding-left:20px;'>{{row.dt_heard|date:"D m/d H:i"}}</td>

    </tr>

{% endfor %}

[esteem learning center]

If you want to do some basic django calculations, you can use django-mathfilters is simple to use for add, subtract, mul, and div

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