Django问题：ManyToMany字段返回非定义字段及多选分数求和存储

Hey there! Let's tackle your two Django issues one by one—since you're new to the framework, I'll keep things clear and actionable.

If your ManyToMany field is returning fields you didn't define, here are the most common causes and straightforward fixes:

Common Reasons & Solutions #

• Over-inclusive Serialization/Querying: If you're using Django REST Framework serializers or fetching related objects without limiting fields, you might be pulling in extra data from the linked model.

  • Fix for Serializers: Explicitly list the fields you need instead of using __all__:

    from rest_framework import serializers
    from .models import Asset
    
    class AssetSerializer(serializers.ModelSerializer):
        class Meta:
            model = Asset
            fields = ['id', 'selected_ff', 'total_score']  # Only include your desired fields
    

  • Fix for Template/View Output: When rendering data, avoid accessing unrelated attributes of linked objects. For example, if you only need the FF name, use {{ ff.ff }} instead of dumping the entire related object.

• Incorrect Model Setup: Double-check your ManyToMany field definition to ensure you're only linking to the intended model (your FF model). A misconfigured related_name or accidental model association can also pull in extra fields.

First, let's align your model structure with the data you described (this will make the calculation logic work smoothly):

from django.db import models

class RType(models.Model):
    rtype_name = models.CharField(max_length=50, unique=True)
    rtype_score = models.IntegerField()

    def __str__(self):
        return self.rtype_name

class FF(models.Model):
    ff = models.CharField(max_length=50, unique=True)
    ff_score = models.ForeignKey(RType, on_delete=models.CASCADE)  # Links FF to its corresponding RType

    def __str__(self):
        return self.ff

class Asset(models.Model):
    selected_ff = models.ManyToManyField(FF)
    total_score = models.IntegerField(default=0)  # Field to store the calculated total

    def __str__(self):
        return f"Asset {self.id} - Total Score: {self.total_score}"

Now, here's how to calculate the total score when the form is submitted:

Option 1: Using a Function-Based View #

If you're working with a basic function view, handle the calculation right after form validation:

from django.shortcuts import render, redirect
from .forms import AssetForm

def create_asset(request):
    if request.method == 'POST':
        form = AssetForm(request.POST)
        if form.is_valid():
            # Save the Asset without committing to the database yet
            asset = form.save(commit=False)
            
            # Calculate total score from selected FF entries
            total = 0
            for ff in form.cleaned_data['selected_ff']:
                total += ff.ff_score.rtype_score  # Grab the RType score linked to each selected FF
            asset.total_score = total
            
            # Save the Asset and then the ManyToMany relationships
            asset.save()
            form.save_m2m()  # Required when using commit=False with ManyToMany fields
            
            return redirect('asset_list')  # Redirect to your asset list page
    else:
        form = AssetForm()
    
    return render(request, 'assets/create_asset.html', {'form': form})

Option 2: Using a Class-Based View (e.g., CreateView) #

If you prefer class-based views, override the form_valid method to add the calculation logic:

from django.views.generic.edit import CreateView
from .models import Asset
from .forms import AssetForm

class AssetCreateView(CreateView):
    model = Asset
    form_class = AssetForm
    success_url = '/assets/'  # Update to your actual success URL

    def form_valid(self, form):
        # Calculate total score before saving the object
        self.object = form.save(commit=False)
        total = sum(ff.ff_score.rtype_score for ff in form.cleaned_data['selected_ff'])
        self.object.total_score = total
        self.object.save()
        form.save_m2m()
        return super().form_valid(form)

Key Notes #

• If you're using a ModelForm for Asset, the selected_ff field will be included by default—no extra setup needed.
• When updating an existing Asset, repeat the same calculation logic (override form_valid in UpdateView or add it to your update function view) to refresh the total score.

内容的提问来源于stack exchange，提问作者mrzap