如何在Django模板中將我的for回圈的回應數限制為3？-有解無憂

在我當前的 Django 模板中，我使用了兩個模型，它們在我的views.py中定義為：

'tasks' : IndividualTask.objects.all(),
'updates' : TaskUpdate.objects.all(),

我已經設定了信號，以便在有任務更新時創建更新。

目前，我遍歷每個任務，然后是它們的每個更新，并為每個任務提取相關更新，如下所示。

{% for task in tasks %}
{% for update in updates %} 
    {% if task.id == update.task.id %}
        {{ update.update }}
    {% endif %}
{% endfor %} 
{% endfor %}

但是，我想將顯示的更新數量限制為三個。

我曾嘗試使用切片，如下所示，但這會將所有更新限制為所有更新的前 3 個，而不是每個任務更新的前 3 個。

{% for task in tasks %}
{% for update in updates|slice:":3" %} 
    {% if task.id == update.task.id %}
        {{ update.update }}
    {% endif %}
{% endfor %} 
{% endfor %}

Models.py如下：


class IndividualTask(models.Model):
    task = models.CharField( 
        max_length = 256,
        blank=False,
        null=True,
        )

    task_description = models.CharField(
        max_length = 256,
        blank=False,
        null=True,
        )

    expected_completion = models.DateField(
        max_length = 64,
        null=True,
        )

    goal = models.ForeignKey(
        IndividualGoal,
        on_delete=models.CASCADE,
        related_name="goals",
        blank=False,
        null=True,
    )

    creator = models.ForeignKey(
        User,
        on_delete=models.CASCADE,
        related_name="creator",
        blank=False,
        null=True,
    )

    owner = models.ForeignKey(
        User,
        on_delete=models.CASCADE,
        blank=False,
        null=True,
    )


    status_choices = [
        ("", "Select Current Status"),
        ("Preparation", "Preparation"),
        ("Review", "Review"),
        ("Update", "Update"),
        ("Finalised", "Finalised"),
    ]

    current_status = models.CharField(
        max_length=32,
        choices = status_choices,
        default = "Select current status",
    )

    created = models.DateField(
        auto_now_add = True,
    )

    def __str__(self):
        return f"{self.task}"

class TaskUpdate(models.Model):
    update = models.CharField(
        max_length = 5000,
    )

    task = models.ForeignKey(
        IndividualTask,
        on_delete=models.CASCADE,
        null = True,
    )

    update_created = models.DateField(
        auto_now_add = True,
    )

    update_time_created = models.TimeField(
        auto_now_add = True,
    )

    author = models.ForeignKey(
        User,
        on_delete=models.CASCADE,
        related_name="update_author",
        blank=True,
        null=True,
    )

    update_choices = [
        ("New Task", "New Task"),
        ("New Commentary", "New Commentary"),
    ]

    update_status = models.CharField(
        max_length=32,
        choices = update_choices,
        null = True,
    )

    class Meta:
        ordering = ["-update_created", "-update_time_created"]

對于如何將每個任務顯示的更新數量限制為 3 的任何建議，我將不勝感激？

編輯：

完整回溯如下所示：

Environment:


Request Method: GET
Request URL: http://127.0.0.1:8000/tasks/

Django Version: 4.0.2
Python Version: 3.9.10
Installed Applications:
['tasks.apps.TasksConfig',
 'notes',
 'accounts',
 'django.contrib.admin',
 'django.contrib.auth',
 'django.contrib.contenttypes',
 'django.contrib.sessions',
 'django.contrib.messages',
 'django.contrib.staticfiles']
Installed Middleware:
['django.middleware.security.SecurityMiddleware',
 'django.contrib.sessions.middleware.SessionMiddleware',
 'django.middleware.common.CommonMiddleware',
 'django.middleware.csrf.CsrfViewMiddleware',
 'django.contrib.auth.middleware.AuthenticationMiddleware',
 'django.contrib.messages.middleware.MessageMiddleware',
 'django.middleware.clickjacking.XFrameOptionsMiddleware']


Template error:
In template /Users/Tom/Desktop/squeasy/tasks/templates/tasks/tasks.html, error at line 69
   'RelatedManager' object is not iterable
   59 :                         Expected Completion Date
   60 :                     </div>
   61 :                     <div class = expected_completion>
   62 :                     {{ task.expected_completion }}
   63 :                     </div>
   64 :                 </div>
   65 :             </div>
   66 :             <div class = task_sub_header>
   67 :                 Latest updates:
   68 :             </div>
   69 :                  {% for update in task.taskupdate_set|slice:":3" %} 
   70 :                     {% if task.id == update.task.id %}
   71 :                     <div class = individual_update>
   72 :                         {% if update.update_status == "New Task" %}
   73 :                             {{ update.author }} created this task on {{ update.update_created|date:"l jS F" }} at {{ update.update_time_created|time:"H:i" }}
   74 :                         {% elif update.update_status == "New Commentary" %}
   75 :                             {{ update.author }} updated the commentary for {{ update.task }} on {{ update.update_created|date:"l jS F" }} at {{ update.update_time_created|time:"H:i" }}
   76 :                         {% endif %}
   77 :                     </div>
   78 :                     {% endif %}
   79 :                 {% endfor %} 


Traceback (most recent call last):
  File "/usr/local/lib/python3.9/site-packages/django/core/handlers/exception.py", line 47, in inner
    response = get_response(request)
  File "/usr/local/lib/python3.9/site-packages/django/core/handlers/base.py", line 181, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/Users/Tom/Desktop/squeasy/tasks/views.py", line 28, in tasks
    return render(request, "tasks/tasks.html", context)
  File "/usr/local/lib/python3.9/site-packages/django/shortcuts.py", line 19, in render
    content = loader.render_to_string(template_name, context, request, using=using)
  File "/usr/local/lib/python3.9/site-packages/django/template/loader.py", line 62, in render_to_string
    return template.render(context, request)
  File "/usr/local/lib/python3.9/site-packages/django/template/backends/django.py", line 61, in render
    return self.template.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 176, in render
    return self._render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 168, in _render
    return self.nodelist.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 977, in render
    return SafeString(''.join([
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 978, in <listcomp>
    node.render_annotated(context) for node in self
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 938, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/loader_tags.py", line 153, in render
    return compiled_parent._render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 168, in _render
    return self.nodelist.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 977, in render
    return SafeString(''.join([
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 978, in <listcomp>
    node.render_annotated(context) for node in self
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 938, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/loader_tags.py", line 65, in render
    result = block.nodelist.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 977, in render
    return SafeString(''.join([
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 978, in <listcomp>
    node.render_annotated(context) for node in self
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 938, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/defaulttags.py", line 298, in render
    return nodelist.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 977, in render
    return SafeString(''.join([
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 978, in <listcomp>
    node.render_annotated(context) for node in self
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 938, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/defaulttags.py", line 217, in render
    nodelist.append(node.render_annotated(context))
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 938, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/defaulttags.py", line 217, in render
    nodelist.append(node.render_annotated(context))
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 938, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/defaulttags.py", line 298, in render
    return nodelist.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 977, in render
    return SafeString(''.join([
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 978, in <listcomp>
    node.render_annotated(context) for node in self
  File "/usr/local/lib/python3.9/site-packages/django/template/base.py", line 938, in render_annotated
    return self.render(context)
  File "/usr/local/lib/python3.9/site-packages/django/template/defaulttags.py", line 173, in render
    values = list(values)

Exception Type: TypeError at /tasks/
Exception Value: 'RelatedManager' object is not iterable

uj5u.com熱心網友回復：

在背景關系中，您可以使用物件 ^[Django-doc]按降序傳遞IndividualTasks ：TaskUpdatePrefetch

from django.db.models import Prefetch

context = {
    'tasks' : IndividualTask.objects.prefetch_related(
                  Prefetch('taskupdate_set', TaskUpdate.objects.order_by('-update_created', '-update_time_created'))
              )
}

然后在模板中列舉taskupdate_set：

{% for task in tasks %}
    {% for update in task.taskupdate_set.all|slice:":3" %}
        {{更新.更新}}
    {% endfor %}
{%endfor %}

注意：通常使用^[Django-doc]參考用戶模型比直接使用模型 ^[Django-doc]更好。有關更多資訊，您可以查看檔案的參考模型部分。settings.AUTH_USER_MODEL UserUser

轉載請註明出處，本文鏈接：https://www.uj5u.com/gongcheng/479429.html

標籤：Python django for循环 django模型

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