它应该是：

company.parentcompany.companyName

不需要使用parentcompany_id，Django会自动检索链接对象。

而不是传递**{{company.parentcompany_id.companyName}}传递{{company.parentcompany.companyName}}**

models.py

class ComapnyModel(models.Model):
    name = models.CharField(max_length=100)
    email = models.EmailField()
    contact = models.CharField(max_length=12)
    parentcompany = models.ForeignKey('self',on_delete=models.CASCADE, blank=True, null=True)

views.py

def DemoView(request):
  data = ComapnyModel.objects.all()
  context = {
      'data': data
  }
  return render(request, 'index.html', context)

HTML代码

<div class="container p-5">
  <div class="row mx-auto">
    <div class="col-12">
      <table class="table">
        <thead>
          <tr>
            <th scope="col">No.</th>
            <th scope="col">Name</th>
            <th scope="col">E-Mail</th>
            <th scope="col">Contact</th>
            <th scope="col">Parent Company</th>
          </tr>
        </thead>
        <tbody>
          {% for i in data %}
          <tr>
            <td>{{forloop.counter}}</td>
            <td>{{i.name}}</td>
            <td>{{i.email}}</td>
            <td>{{i.contact}}</td>
            <td>
              {% if i.parentcompany %}
              {{i.parentcompany.name}}
              {% else %}
              <span><i> - </i></span>
              {% endif %}
            </td>
          </tr>
          {% endfor %}
        </tbody>
      </table>
    </div>
  </div>
</div>

浏览器输出