以一种形式组合两个模型？

Question

我正在创建一个发票应用程序。我希望能够在发票中添加一些项目。为此，该应用程序提供了两种模型：Invoice和InvoiceItem。我已将两种模型合并为一种形式。我现在想要实现的是能够在发票表格的表中添加一些项目。目前，我只能添加一项​​。我已经在表单中添加了一个按钮来添加新项目，但是s getting confusing and I wonder if there is a different way to achieve this. The button doesn目前不起作用，表中的项目也是如此。

非常感谢，

models.py

class Invoice(models.Model):
    TERMS = (      
        (0, '30 days'),
        (1, '45 days'),
        (2, '60 days'),        
        )
    user = models.ForeignKey(User, default=1, on_delete=models.CASCADE)
    currency = models.ForeignKey(Currency, on_delete=models.CASCADE, blank=True, null=True)
    project = models.ForeignKey(Project, on_delete=models.CASCADE, blank=True, null=True)
    address = models.ForeignKey(Company, on_delete=models.CASCADE, blank=True, null=True)
    invoice_id = models.CharField(unique=True, max_length=6, null=True, blank=True, editable=False)
    invoice_date = models.DateField(_("Date"), default=datetime.date.today)
    invoiced = models.BooleanField(default=False)

class InvoiceItem(models.Model):
    invoice = models.ForeignKey(Invoice, on_delete=models.CASCADE, blank=True, null=True)
    description = models.CharField(max_length=100)
    unit_price = models.DecimalField(max_digits=8, decimal_places=2)
    quantity = models.DecimalField(max_digits=8, decimal_places=2, default=1)
    vat = models.CharField(max_length=250)
    total = models.CharField(max_length=250)

views.py

def create_invoice(request):
    form = InvoiceForm(request.POST or None, request.FILES or None)
    if request.method == 'POST':
        invoice_form = InvoiceForm(request.POST)
        invoiceitem_form = InvoiceItemForm(request.POST)
        if invoice_form.is_valid() and invoiceitem_form.is_valid():
            invoice_form.save()
            invoiceitem_form.save()
            return HttpResponseRedirect('/success')        
        else:
            context = {
                'invoice_form': invoice_form,
                'invoiceitem_form': invoiceitem_form,
            }
    else:
        context = {
            'invoice_form': InvoiceForm(),
            'invoiceitem_form': InvoiceItemForm(),
        }
    return render(request, 'invoices/create_invoice.html', context)

forms.py

class InvoiceForm(forms.ModelForm):

    class Meta:
        model = Invoice
        fields = ['project','invoice_date','address','invoiced']   

class InvoiceItemForm(forms.ModelForm):

    class Meta:
        model = InvoiceItem
        fields = ['description','quantity','unit_price',] 

create_invoice.html

{% extends 'base.html' %}
{% block title %}New Invoice{% endblock %}
{% block invoices_active %}active{% endblock %}

{% load crispy_forms_tags %}

{% block body %}
<div class="container-fluid">
    <div class="row">
        <div class="col-sm-3"></div>
        <div class="col-sm-12 col-md-6">
            <div class="jumbotron text-center" style="padding: 0.5em 0.6em; h1 {font-size: 2em;}">
                <h1>New Invoice</h1>
            </div>
            <div class="card">
                <div class="card-header">Invoice Details</div>      
                <div class="card-body">                    
                    {% if error_message %}
                        <p><strong>{{ error_message }}</strong></p>
                    {% endif %}
                    <form class="form-horizontal" role="form" action="" method="post" enctype="multipart/form-data">
                        {% csrf_token %}
                        {{ invoice_form.as_p }}
                        <a href="" class="btn btn-sm btn-primary btn-create" role="button">New Item</button></a>
                        <table id="dtBasic" class="table table-striped table-hover">               
                            <thead>
                                    <tr>
                                        <th>#</th>
                                        <th>Description</th>
                                        <th>Unit Price</th>
                                        <th>Quantity</th>                                         
                                    </tr>
                                    </thead>
                                    <tbody> 
                                  //This is wrong below
                                    ***{% for invoiceitem in invoiceitems.all %}
                                        <tr>                                                              
                                            <td>{{ form.invoiceitem.id }}</td>
                                            <td>{{ form.invoiceitem.description }}</td>
                                            <td>{{ form.invoiceitem.unitprice }}</td>
                                            <td>{{ form.invoiceitem.quantity }}</td>                                             
                                        </tr>
                                    {% endfor %}***
                                             
                                    </tbody>
                                </table>
                        {{ invoiceitem_form.as_p }}
                        <button type="submit"></button>
                    </form>
                </div>
            </div>
        </div>       

    </div>

</div>
{% endblock %}