Python : How to pass the value of a foreign key in my Django template?

Question

I have created a Bid model so that type-2 users can bid on some 'Post' created by type-1 users. For achieving this, I made a foreign key for post field in the model 'Bid'.

Actually i wanted to relate the bids to a particular post with auto generated 'id' in the 'post' model. So i placed the get_absolute_url beside Post 'id' in my template. I am new to django and I am not sure whether it works for what i want or not.

How can i relate the bid with post_id to a particular post in the template so that i can get a bid amount placed by various type-2 users for a particular post? I would appreciate helping me solve this.

Here's my code:

Models.py:

class Post(models.Model):

    post_id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    user = models.ForeignKey(settings.AUTH_USER_MODEL, default=1)
    from1 = models.CharField(max_length=20)
    timestamp = models.DateTimeField(auto_now=False, auto_now_add=True)

    objects = PostManager()

    def __str__(self):
        return self.post_id

    def get_absolute_url(self):
        return reverse("posts:detail", kwargs={"id": self.post_id})

    class Meta:
        ordering = ["-timestamp", "-Time"]

class Bid(models.Model):

    bid_id = models.UUIDField(primary_key=True, default=uuid.uuid4, editable=False)
    post = models.ForeignKey(Post, default=uuid.uuid4, related_name='bids' )
    user = models.OneToOneField(settings.AUTH_USER_MODEL, null=True, blank=True, unique=False)
    amount = models.IntegerField()

    def get_absolute_url(self):
        return reverse("accept_bid", kwargs={"bid_id": self.bid_id})

    def __unicode__(self):
        return self.amount

    def __str__(self):
        return self.amount

forms.py:

class BidForm(forms.ModelForm):
    // Defined a post field as ModelChoiceField
    post = forms.ModelChoiceField(queryset= Post.objects.all(), label="Post", widget=forms.RadioSelect(), initial=0)
    amount = forms.IntegerField(help_text='Place the bid for a Post')

    def __init__(self, *args, **kwargs):
        self.request = kwargs.pop('request', None)
        super(BidForm, self).__init__(*args, **kwargs)
        self.fields['post'].queryset = Post.objects.all

    class Meta:
        model = Bid
        fields = ["amount"]

views.py:

def live_bid_truck(request, **kwargs):
    if request.method=='post':
        form = BidForm(request.POST or None)

        if  form.is_valid():
         bid = form.save(post)
         bid = form.save(commit=False)
         print(form.cleaned_data.get('amount'))
         bid.user = request.user
         bid.post = form.cleaned_data['post'] // Set my post here


         bid.save()
    else:
        form=BidForm()
        post_queryset = Post.objects.all()
        context = {
        "post_queryset": post_queryset, 
        "title": "List",
        'form': form,

    }
        return render(request, 'loggedin_truck/live_bid_truck.html', context)

live_bid_truck.html

{% for post in post_queryset %}
<table class="table table-striped, sortable">
    <thead>
        <tr>

            <th>Load No.</th>
            <th>From</th>
        </tr>
    </thead>
    <tbody>
        <tr> // Returns the post_queryset with radio buttons
            <td >{{form.post}} </td>
            <td>{{ post.from1 }}</a><br/></td>
        </tr> 
    </tbody>
</table>
<table class="table table-striped, sortable "  style="margin-top: 10px">
    <thead>
        <tr>
            <th> Amount</th>
        </tr>
    </thead>
    <tbody>
        <tr>     
            <form class="nomargin" method='POST' action='' enctype='multipart/form-data'>{% csrf_token %}
            <td>{% render_field  form.amount  class="form-control" %}</td>
        </tr>
     </tbody>
 </table>

<input type='submit' value='Post Bid'/></form>

{% endfor %}

Update - 1:

Views.py:

def live_bids(request):
    post_queryset = Post.objects.all().prefetch_related('bids')
    bid_queryset = Bid.objects.all().order_by('amount')

    context = {
        "post_queryset": post_queryset,
        "bid_queryset": bid_queryset,
        "title": "List",
    }
    return render(request, 'loggedin_load/live_bids.html', context)

live_bids.html:

{% for post in post_queryset %}
{{post.id}}
{% for bid in post.bids.all %}
{{bid.amount}}
{% endfor %}
{% endfor %}

Answer 1

If I understood correctly, the goal is to be able to list the related bidders/bids on the post? If so, then you can use select_related (if you're selecting parents from child) of prefetch_related (if you're doing a reverse lookup)

1) First of all in your Bid model better related_name would be "bids", like so;

post = models.ForeignKey(Post, default=1, related_name='bids' )

2) Secondly inside def live_bid_truck(request): make the post query like this so that you would get all the related objects in one database hit.;

Post.objects.all().prefetch_related('bids') 

3) Then in your template you can use can access the related bids for the post

{% for bid in post.bids.all %} // In your case post is obj
    {{ bid }}  // Access whatever you need from the bid like {{ bid.user }}
{% endfor %}

You should be able to call post.bids.all and receive values even without prefetch by just following the backward relation. If you're not getting any values, then you probably are not setting them properly. prefetch_related helps with the performance as the number of posts increase.

---

FROM YOUR CODE

In your BidForm there is no reference to the post and I don't know if you have it in your custom save() method or not. When you save this form as it is, post_id will be the default value 1

# NO REFENCE TO post
class BidForm(forms.ModelForm):

 class Meta:
    model = Bid
    fields = ["amount"]  

Also in your view you don't set the post either.

def live_bid_truck(request):

    form = BidForm(request.POST or None)

    if  form.is_valid():
        bid = form.save(commit=False)

        print(form.cleaned_data.get("amount"))
        bid.user = request.user # YOU SET THE USER 
        bid.post = ?? # YOU DON'T SET THE POST HERE EITHER, 
                      # SO ALL YOUR BIDS HAVE THE DEFAULT POST id = 1
                      # DO YOU ACTUALLY HAVE POST with id = 1?

        bid.save()

        # WHAT HAPPENS IF YOU PRINT BID POST ID HERE ?? 
        # CHECK HERE IF YOU REALLY HAVE THE RELATED POST ID.
        print(bid.post.id)