Django中实现每日数据最大值与平均值展示的类及视图求助

Hey there! As someone new to Python and Django, I get that figuring out how to aggregate and display daily stats can feel overwhelming at first. Let’s walk through this step by step, starting with the simplest approach that doesn’t require extra models, then moving to a more scalable option if you need it later.

If your dataset isn’t huge (like hundreds of entries per day max), you can use Django’s built-in aggregation functions to calculate daily averages and max values directly when someone visits the stats page.

Step 1: Write the View #

In your app’s views.py, add this function:

from django.db.models import Avg, Max, TruncDate
from django.utils import timezone
from django.shortcuts import render
from .models import Entry

def daily_stats(request):
    # Group entries by date, then compute averages and maxes for each field
    daily_data = Entry.objects.annotate(
        # Truncate the `time` field to just the date part for grouping
        date=TruncDate('time')
    ).values('date').annotate(
        # Calculate averages and maxes for each metric
        avg_inside=Avg('inside'),
        max_inside=Max('inside'),
        avg_outside=Avg('outside'),
        max_outside=Max('outside'),
        avg_gavg=Avg('gavg'),
        max_gavg=Max('gavg'),
        avg_ghigh=Avg('ghigh'),
        max_ghigh=Max('ghigh')
    ).order_by('-date')  # Show newest dates first

    # Pass the stats to your template
    return render(request, 'daily_stats.html', {'daily_data': daily_data})

Step 2: Create a Template #

Make a daily_stats.html file in your app’s templates folder to display the data:

<h1>Daily Temperature & G-Metric Stats</h1>
<table style="border-collapse: collapse; width: 100%; margin-top: 20px;">
    <thead>
        <tr style="border-bottom: 2px solid #ddd;">
            <th style="padding: 8px; text-align: left;">Date</th>
            <th style="padding: 8px; text-align: right;">Avg Inside</th>
            <th style="padding: 8px; text-align: right;">Max Inside</th>
            <th style="padding: 8px; text-align: right;">Avg Outside</th>
            <th style="padding: 8px; text-align: right;">Max Outside</th>
            <th style="padding: 8px; text-align: right;">Avg Gavg</th>
            <th style="padding: 8px; text-align: right;">Max Gavg</th>
            <th style="padding: 8px; text-align: right;">Avg Ghigh</th>
            <th style="padding: 8px; text-align: right;">Max Ghigh</th>
        </tr>
    </thead>
    <tbody>
        {% for stats in daily_data %}
        <tr style="border-bottom: 1px solid #eee;">
            <td style="padding: 8px;">{{ stats.date|date:"Y-m-d" }}</td>
            <td style="padding: 8px; text-align: right;">{{ stats.avg_inside|floatformat:2 }}</td>
            <td style="padding: 8px; text-align: right;">{{ stats.max_inside|floatformat:2 }}</td>
            <td style="padding: 8px; text-align: right;">{{ stats.avg_outside|floatformat:2 }}</td>
            <td style="padding: 8px; text-align: right;">{{ stats.max_outside|floatformat:2 }}</td>
            <td style="padding: 8px; text-align: right;">{{ stats.avg_gavg|floatformat:0 }}</td>
            <td style="padding: 8px; text-align: right;">{{ stats.max_gavg }}</td>
            <td style="padding: 8px; text-align: right;">{{ stats.avg_ghigh|floatformat:0 }}</td>
            <td style="padding: 8px; text-align: right;">{{ stats.max_ghigh }}</td>
        </tr>
        {% empty %}
        <tr>
            <td colspan="9" style="padding: 16px; text-align: center;">No data available yet. Check back after your first 5-minute entry!</td>
        </tr>
        {% endfor %}
    </tbody>
</table>

Step 3: Add a URL #

In your app’s urls.py, map the view to a URL so users can access it:

from django.urls import path
from .views import daily_stats

urlpatterns = [
    # ... your other URLs go here
    path('daily-stats/', daily_stats, name='daily_stats'),
]

If you end up with thousands of entries per day, calculating stats on-the-fly might slow down your page. Instead, we can precompute and store daily stats in a separate model, then just query that model for display.

Step 1: Create a Daily Stats Model #

Add this to your models.py:

from django.db import models
from django.utils import timezone

class DailyStats(models.Model):
    date = models.DateField(unique=True)  # One entry per date
    avg_inside = models.FloatField()
    max_inside = models.FloatField()
    avg_outside = models.FloatField()
    max_outside = models.FloatField()
    avg_gavg = models.FloatField()
    max_gavg = models.IntegerField()
    avg_ghigh = models.FloatField()
    max_ghigh = models.IntegerField()

    class Meta:
        ordering = ['-date']  # Newest dates first

    def __str__(self):
        return f"Stats for {self.date}"

Don’t forget to run python manage.py makemigrations and python manage.py migrate to create the table.

Step 2: Write a Function to Compute & Save Stats #

Add this function to your models.py (or a separate utils.py file):

from django.db.models import Avg, Max
from .models import Entry, DailyStats
from django.utils import timezone

def calculate_daily_stats(target_date=None):
    # Default to yesterday if no date is provided
    if not target_date:
        target_date = timezone.now().date() - timezone.timedelta(days=1)

    # Get all entries from the target date
    daily_entries = Entry.objects.filter(time__date=target_date)
    if not daily_entries.exists():
        return  # Skip if there's no data for the date

    # Compute the stats
    stats = daily_entries.aggregate(
        avg_inside=Avg('inside'),
        max_inside=Max('inside'),
        avg_outside=Avg('outside'),
        max_outside=Max('outside'),
        avg_gavg=Avg('gavg'),
        max_gavg=Max('gavg'),
        avg_ghigh=Avg('ghigh'),
        max_ghigh=Max('ghigh')
    )

    # Save or update the stats (prevents duplicate entries)
    DailyStats.objects.update_or_create(
        date=target_date,
        defaults=stats
    )

Step 3: Automate the Calculation #

You’ll want to run this function daily. For simplicity, you can use Django’s django-crontab package to set up a scheduled task:

1. Install it: pip install django-crontab
2. Add it to INSTALLED_APPS in settings.py
3. Add this to settings.py:

   CRONJOBS = [
       # Run at 1 AM every day to compute yesterday's stats
       ('0 1 * * *', 'yourapp.utils.calculate_daily_stats')
   ]
   

4. Run python manage.py crontab add to activate the task.

Step 4: Update the View #

Now your view can just fetch the precomputed stats, which is much faster:

from django.shortcuts import render
from .models import DailyStats

def daily_stats(request):
    daily_data = DailyStats.objects.all()
    return render(request, 'daily_stats.html', {'daily_data': daily_data})

The template from the first approach will work perfectly here—no changes needed!

Either approach will get you up and running. Start with the first one if you’re still learning, and switch to the second if you notice performance issues as your dataset grows.

内容的提问来源于stack exchange，提问作者Blake Russell