Django学习路22_empty为空,forloop.counter 从1计数,.counter0 从0计数 .revcounter最后末尾数字是1,.revcounter0 倒序,末尾为 0

当查找的数据不存在,返回为 空时
在 html 中使用 {%empty%} 语句  进行显示

def getstudents(request):

    students = Student.objects.all().filter(s_name = 'qwer')
    # 指定一个不存在的值,
    # students = Student.objects.all()
    stu_dict = {
    #     自己定义的字典
        'hobby':'play',
        'time':'5 years'
    }

    stu_data = {
        'students':students,
        'stu_dict':stu_dict
    #     stu_dict 是自己定义的字典
    }

    return render(request,'students.html',context=stu_data)

 

html 中语句

    {% for stu in students %}
    <li> {{ stu.s_name }}</li>
        {% empty %}
        <h3>不存在该学生</h3>
    {% endfor %}
    <hr/><br/><br/>
注: 
如果为 空,则输出 <h3> 不存在该学生</h3> 这条语句

---

---

def getstudents(request):

    students = Student.objects.all()
    # 指定一个不存在的值,
    # students = Student.objects.all()
    stu_dict = {
    #     自己定义的字典
        'hobby':'play',
        'time':'5 years'
    }

    stu_data = {
        'students':students,
        'stu_dict':stu_dict
    #     stu_dict 是自己定义的字典
    }

    return render(request,'students.html',context=stu_data)

forloop.counter 示例

    {% for stu in students %}
    <li> {{ forloop.counter }} : {{ stu.s_name }}</li>
    {% endfor %}
  

 

---

forloop.counter0 示例

    {% for stu in students %}
    <li> {{ forloop.counter0 }} : {{ stu.s_name }}</li>
    {% endfor %}

 

---

forloop.revcounter 示例

    {% for stu in students %}
    <li> {{ forloop.revcounter }} : {{ stu.s_name }}</li>
    {% endfor %}

 

---

forloop.revcounter0 示例

    {% for stu in students %}
    <li> {{ forloop.revcounter0 }} : {{ stu.s_name }}</li>
    {% endfor %}

 

---

_2020-05-14