zoukankan      html  css  js  c++  java
  • django获取指定列的数据

    django获取指定列的数据

    model一般都是有多个属性的,但是很多时候我们又只需要查询特定的某一个,这个时候可以用到valuesvalues_list

    [values()](https://docs.djangoproject.com/en/1.9/ref/models/querysets/#values)
    values()¶
    
    values(*fields)¶
    Returns a QuerySet that returns dictionaries, rather than model instances, when used as an iterable.
    
    Each of those dictionaries represents an object, with the keys corresponding to the attribute names of model objects.
    
    [values_list()](https://docs.djangoproject.com/en/1.9/ref/models/querysets/#values-list)
    values_list()¶
    
    values_list(*fields, flat=False)¶
    This is similar to values() except that instead of returning dictionaries, it returns tuples when iterated over. Each tuple contains the value from the respective field passed into the values_list() call — so the first item is the first field, etc.
    

    看下面的代码:

    利用values查询

    from attendence.models import Employee
    from attendence.models import EmployeeIP
    
    #获取一个字段
    ipList = EmployeeIP.objects.values("IP").first()
    print(type(ipList))
    # <class 'dict'>
    print(ipList)
    # {'IP': '192.168.1.41'}
    
    #获取多个字段
    empList = Employee.objects.values("first_name", "last_name", "email")[0:2]
    print(type(empList))
    # <class 'django.db.models.query.QuerySet'>
    print(empList)
    # [
    #   {'last_name': 'Wei', 'first_name': 'Vena', 'email': 'Vena@test.com'},
    #   {'last_name': 'Wan', 'first_name': 'Mark', 'email': 'mwan@test.com'}
    # ]
    

    利用values_list查询

    ipList = EmployeeIP.objects.values_list("IP").first()
    print(type(ipList))
    # <class 'tuple'>
    print(ipList)
    # ('192.168.1.111',)
    
    ipList = EmployeeIP.objects.values_list("IP")[0:2]
    print(type(ipList))
    # <class 'django.db.models.query.QuerySet'>
    print(ipList)
    # [('192.168.1.41',), ('192.168.1.44',)]
    print(type(ipList[0]))
    # <class 'tuple' >
    print(ipList[0])
    # 192.168.1.111
    

    values和values_list的差别

    从上面的代码中我们可以看到返回结果类型上细微的差别

    • vlaues -
      • 单条记录 - <class 'dict'>
      • 多条记录 - <class 'django.db.models.query.QuerySet'>
    • vlaues_list -
      • 单条记录 - <class 'tuple'>
      • 多条记录 - <class 'django.db.models.query.QuerySet'>
  • 相关阅读:
    CoreAnimation6-基于定时器的动画和性能调优
    CoreAnimation5-图层时间和缓冲
    CoreAnimation4-隐式动画和显式动画
    CoreAnimation3-专用图层
    CoreAnimation2-视觉效果和变换
    CoreAnimation1-图层树、寄宿图以及图层几何学
    Quartz-2D绘图之路径(Paths)详解
    Quartz-2D绘图之图形上下文详解
    Objective-C设计模式——抽象工厂模式Abstract Factory(对象创建)
    Objective-C设计模式——工厂方法模式virtual constructor(对象创建)
  • 原文地址:https://www.cnblogs.com/wancy86/p/django_getfield.html
Copyright © 2011-2022 走看看