Django Admin 搜索框占位符实现：自定义 search_fields 提示文字

$ python manage.py startapp carousel
# settings.py
```
INSTALLED_APPS = [
  ...
  'carousel',
]
```
# carousel/models.py
```
from django.db import models
 
class Carousel(models.Model):
  community = models.IntegerField('小区ID')
  
  class Meta:
    verbose_name = verbose_name_plural = '轮播设置'
```

mkdir -p carousel/templatetags
touch carousel/templatetags/__init__.py
touch carousel/templatetags/search_with_placeholder.py

# carousel/templatetags/search_with_placeholder.py
from django.contrib.admin.templatetags.admin_list import (
  InclusionAdminNode,
  register,
  search_form,
)
 
 
def search_form_plus(cl, search_placeholder: str = ""):
  """
  Display a search form for searching the list with placeholder.
  """
  return dict(search_form(cl), search_placeholder=search_placeholder)
 
 
@register.tag(name="search_form_plus")
def search_form_tag(parser, token):
  return InclusionAdminNode(
    parser,
    token,
    func=search_form_plus,
    template_name="search_form_plus.html",
    takes_context=False,
  )

mkdir -p carousel/templates/admin
mkdir -p carousel/templates/custom_admin
touch carousel/templates/admin/search_form_plus.html
touch carousel/templates/custom_admin/change_list.html

<!-- carousel/templates/admin/search_form_plus.html -->
{% load i18n static %}
{% if cl.search_fields %}
<div id="toolbar"><form id="changelist-search" method="get">
<div><!-- DIV needed for valid HTML -->
<label for="searchbar"><img src="{% static "admin/img/search.svg" %}" alt="Search"></label>
<input type="text" size="40" name="{{ search_var }}" placeholder="{{ search_placeholder }}" value="{{ cl.query }}" id="searchbar" autofocus>
<input type="submit" value="{% translate 'Search' %}">
{% if show_result_count %}
  <span class="small quiet">{% blocktranslate count counter=cl.result_count %}{{ counter }} result{% plural %}{{ counter }} results{% endblocktranslate %} (<a href="?{% if cl.is_popup %}_popup=1{% endif %}" rel="external nofollow" >{% if cl.show_full_result_count %}{% blocktranslate with full_result_count=cl.full_result_count %}{{ full_result_count }} total{% endblocktranslate %}{% else %}{% translate "Show all" %}{% endif %}</a>)</span>
{% endif %}
{% for pair in cl.params.items %}
  {% if pair.0 != search_var %}<input type="hidden" name="{{ pair.0 }}" value="{{ pair.1 }}">{% endif %}
{% endfor %}
</div>
</form></div>
{% endif %}

<!-- carousel/templates/custom_admin/change_list.html -->
{% extends "admin/change_list.html" %}
{% load search_with_placeholder %}
 
{% block search %}{% search_form_plus cl search_placeholder %}{% endblock %}

# Django3.1
from django.contrib import admin
 
from .models import BoxCarousel, Carousel,
 
 
class PlaceholderMixin:
  change_list_template = "custom_admin/change_list.html"
 
  def changelist_view(self, request, extra_context=None):
    search_placeholder = getattr(self, "search_placeholder", False)
    if search_placeholder:
      extra_context = extra_context or {}
      extra_context["search_placeholder"] = search_placeholder
    return super().changelist_view(request, extra_context)
 
 
@admin.register(Carousel)
class CarouselAdmin(PlaceholderMixin, admin.ModelAdmin):
  search_fields = ["=community"]
  search_placeholder = "请输入小区ID"