Django模板使用'=='整数比较时渲染报错问题排查

问题描述 #

在Django模板中使用==进行整数比较时触发TemplateSyntaxError，报错提示无法解析==1部分。

视图函数代码 #

def mailtemplate_GetSchema(request, id=None):
  if id == None:
    svars = []
    this_var = {}
    this_var['s_id']=str(uuid4())
    this_var['varname'] = f"varname_{this_var['s_id']}"
    this_var['varlabel'] = f"varlabel_{this_var['s_id']}"
    this_var['vartype'] = f"vartype_{this_var['s_id']}"
    this_var['varformat'] = f"varformat_{this_var['_sid']}"
    this_var['varname_value'] = ''
    this_var['varlabel_value'] = ''
    this_var['vartype_value'] = 1
    this_var['varformat_value'] = ''
    svars.append(this_var)

    return render(request, 'mailtemplate_all.html', {'svars': svars})

  try :
    obj = MailTemplate.objects.get(pk=id)
    schema = obj.schema
    schema = json.loads(schema)
    # it's a list of dictionary
    vars = []
    for s in schema:
      this_var = {}
      this_var['field_id']=str(uuid4())
      this_var['varname'] = f"varname_{this_var['field_id']}"
      this_var['varlabel'] = f"varlabel_{this_var['field_id']}"
      this_var['vartype'] = f"vartype_{this_var['field_id']}"
      this_var['varformat'] = f"varformat_{this_var['field_id']}"
      this_var['varname_value'] = s.get('name','')
      this_var['varlabel_value'] = s.get('label','')
      this_var['vartype_value'] = s.get('type',1)
      this_var['varformat_value'] = s.get('format',None)
      if this_var['varformat_value'] == '':
        this_var['varformat_value']=False
      vars.append(this_var)

    print(f'VARS:{vars}')
    return render(request, 'mailtemplate_all.html', {'vars': vars})

  except MailTemplate.DoesNotExist:
    return HttpResponseNotFound()

模板文件mailtemplate_all.html代码 #

{% for v in vars%}
<div id={{ v.field_id }} class="divTableRow">
  <div class="divTableCell">
    <input type="text" name={{v.varname}} value={{ v.varname_value}} class="vTextField" maxlength="20" >
  </div>

  <div class="divTableCell">
    <input type="text" name={{v.varlabel}} value={{ v.varlabel_value}} class="vTextField" maxlength="20" >
  </div>

  <div class="divTableCell">
    <select name={{v.vartype}}>
      {% if v.vartype_value==1 %}
        <option value=1 selected>
      {% else %}
        <option value=1>
      {% endif %}
      Integer</option>

      {% if v.vartype_value==2 %}
        <option value=2 selected>
      {% else %}
        <option value=2>
      {% endif %}
      String</option>

      {% if v.vartype_value==3 %}
        <option value=3 selected>
      {% else %}
        <option value=3>
      {% endif %}
      Date</option>

    </select>
  </div>

  <div class="divTableCell">
    <input type="text" name={{v.varformat}} {% if v.varformat_value %}value={{v.varformat_value}}{% endif %}  class="vTextField" maxlength="20" >
  </div>
</div>
{% endfor %}

报错信息 #

[13/Jan/2023 08:23:12] "GET /static/admin/fonts/Roboto-Bold-webfont.woff HTTP/1.1" 200 86184
VARS:[{'field_id': 'ac9a3707-3906-4e75-9efd-514959056ddb', 'varname': 'varname_ac9a3707-3906-4e75-9efd-514959056ddb', 'varlabel': 'varlabel_ac9a3707-3906-4e75-9efd-514959056ddb', 'vartype': 'vartype_ac9a3707-3906-4e75-9efd-514959056ddb', 'varformat': 'varformat_ac9a3707-3906-4e75-9efd-514959056ddb', 'varname_value': 'kepada', 'varlabel_value': 'Kepada', 'vartype_value': 2, 'varformat_value': False}]
Internal Server Error: /mst/htmx/get_schema/2
Traceback (most recent call last):
  File "/home/bino/.venv/htmx01/lib/python3.10/site-packages/django/template/smartif.py", line 179, in translate_token
    op = OPERATORS[token]
KeyError: 'v.vartype_value==1'

During handling of the above exception, another exception occurred:

Traceback (most recent call last):
  File "/home/bino/.venv/htmx01/lib/python3.10/site-packages/django/core/handlers/exception.py", line 55, in inner
    response = get_response(request)
  File "/home/bino/.venv/htmx01/lib/python3.10/site-packages/django/core/handlers/base.py", line 197, in _get_response
    response = wrapped_callback(request, *callback_args, **callback_kwargs)
  File "/home/bino/Documents/dynform/htmx01/myapp/views.py", line 48, in mailtemplate_GetSchema
    return render(request, 'mailtemplate_all.html', {'vars': vars})
...
  File "/home/bino/.venv/htmx01/lib/python3.10/site-packages/django/template/smartif.py", line 181, in translate_token
    return self.create_var(token)
  File "/home/bino/.venv/htmx01/lib/python3.10/site-packages/django/template/defaulttags.py", line 889, in create_var
    return TemplateLiteral(self.template_parser.compile_filter(value), value)
  File "/home/bino/.venv/htmx01/lib/python3.10/site-packages/django/template/base.py", line 600, in compile_filter
    return FilterExpression(token, self)
  File "/home/bino/.venv/htmx01/lib/python3.10/site-packages/django/template/base.py", line 703, in __init__
    raise TemplateSyntaxError(
django.template.exceptions.TemplateSyntaxError: Could not parse the remainder: '==1' from 'v.vartype_value==1'
[13/Jan/2023 08:23:12] "GET /mst/htmx/get_schema/2 HTTP/1.1" 500 200297
Not Found: /favicon.ico
[13/Jan/2023 08:23:12] "GET /favicon.ico HTTP/1.1" 404 2212

测试情况 #

将视图输出的vars数据取出，使用Jinja2测试相同模板，渲染正常且输出符合预期：

(htmx01)  bino@corobalap  ~/Documents/dynform/htmx01  python3
Python 3.10.6 (main, Nov 14 2022, 16:10:14) [GCC 11.3.0] on linux
Type "help", "copyright", "credits" or "license" for more information.
>>> from jinja2 import Template
>>> vars=[{'field_id': 'ac9a3707-3906-4e75-9efd-514959056ddb', 'varname': 'varname_ac9a3707-3906-4e75-9efd-514959056ddb', 'varlabel': 'varlabel_ac9a3707-3906-4e75-9efd-514959056ddb', 'vartype': 'vartype_ac9a3707-3906-4e75-9efd-514959056ddb', 'varformat': 'varformat_ac9a3707-3906-4e75-9efd-514959056ddb', 'varname_value': 'kepada', 'varlabel_value': 'Kepada', 'vartype_value': 2, 'varformat_value': False}]
>>> with open('myapp/templates/mailtemplate_all.html','r') as tfile:
...     template = Template(tfile.read())
... 
>>> o=template.render(vars=vars)
>>> print(o)


<div id=ac9a3707-3906-4e75-9efd-514959056ddb class="divTableRow">
  <div class="divTableCell">
    <input type="text" name=varname_ac9a3707-3906-4e75-9efd-514959056ddb value=kepada class="vTextField" maxlength="20" >
  </div>

  <div class="divTableCell">
    <input type="text" name=varlabel_ac9a3707-3906-4e75-9efd-514959056ddb value=Kepada class="vTextField" maxlength="20" >
  </div>

  <div class="divTableCell">
    <select name=vartype_ac9a3707-3906-4e75-9efd-514959056ddb>
      
        <option value=1>
      
      Integer</option>

      
        <option value=2 selected>
      
      String</option>

      
        <option value=3>
      
      Date</option>

    </select>
  </div>

  <div class="divTableCell">
    <input type="text" name=varformat_ac9a3707-3906-4e75-9efd-514959056ddb   class="vTextField" maxlength="20" >
  </div>
</div>

>>> 
>>> 

问题原因与解决方案 #

视图代码本身没有问题，错误出在Django模板的比较语法规则上：Django要求比较运算符==的两边必须添加空格，不能像Jinja2那样直接写v.vartype_value==1，正确格式应为v.vartype_value == 1。

修改模板中的if条件语句，给==两边加上空格即可解决：

<select name={{v.vartype}}>
  {% if v.vartype_value == 1 %}
    <option value=1 selected>
  {% else %}
    <option value=1>
  {% endif %}
  Integer</option>

  {% if v.vartype_value == 2 %}
    <option value=2 selected>
  {% else %}
    <option value=2>
  {% endif %}
  String</option>

  {% if v.vartype_value == 3 %}
    <option value=3 selected>
  {% else %}
    <option value=3>
  {% endif %}
  Date</option>
</select>

另外，也可以使用Django模板专属的{% ifequal %}标签替代==比较，写法如下：

{% ifequal v.vartype_value 1 %}
  <option value=1 selected>
{% else %}
  <option value=1>
{% endifequal %}

内容的提问来源于stack exchange，提问作者Bino Oetomo