Django:values_list()连接多个字段

Question

我有一个Person模型,我使用django表单编辑另一个带有外键的对象Person.人物模型有first_name和last_name字段.我想运行一个方法来过滤外部引用的下拉框的结果.

我试图用来values_list()覆盖表单字段选项(选择属性),如下所示:

data.form.fields['person'].choices = GetPersons().values_list('id', 'first_name')

GetPersons() 只过滤Person类

return Person.objects.filter(id__gt=1000)`

例如,所以我只会找到我想要出现的人.我如何使用values_list()返回连接first_name和last_name不必返回字典并手动拆分所有内容？

Answer 1

我想到了2个sugestions:

• 第一个是将数据库中的字段与extra连接起来.对我来说是一个肮脏的解决方案但可以运行

样品:

persons =  GetPersons().extra(select={'full_name': "concatenate( first, last) "} )
choices = persons.values_list('id', 'full_name')

和......

• 第二个使用列表理解:

样品:

choices = [ ( p.id, '{0} {1}'.format( p.first, p.last ),) for p in GetPersons() ]

编辑2018年

Concat现在可用作数据库功能:

>>> from django.db.models import CharField, Value as V
>>> from django.db.models.functions import Concat
>>> persons = GetPersons().annotate(
...     full_name=Concat(
...         'last', V(', '), 'first', V('.'),
...         output_field=CharField()
...     )
... )

Answer 2

听起来这个annotate()功能在Django 1.8中变得更加灵活.您可以将两个字段与Concat表达式组合,然后使用该表达式注释查询集.

# Tested with Django 1.9.2
import sys

import django
from django.apps import apps
from django.apps.config import AppConfig
from django.conf import settings
from django.db import connections, models, DEFAULT_DB_ALIAS
from django.db.models.base import ModelBase
from django.db.models.functions import Concat, Value

NAME = 'udjango'


def main():
    setup()

    class Person(models.Model):
        first_name = models.CharField(max_length=30)
        last_name = models.CharField(max_length=30)

    syncdb(Person)

    Person.objects.create(first_name='Jimmy', last_name='Jones')
    Person.objects.create(first_name='Bob', last_name='Brown')

    print(Person.objects.annotate(
        full_name=Concat('first_name',
                         Value(' '),
                         'last_name')).values_list('id', 'full_name'))
    # >>> [(1, u'Jimmy Jones'), (2, u'Bob Brown')]


def setup():
    DB_FILE = NAME + '.db'
    with open(DB_FILE, 'w'):
        pass  # wipe the database
    settings.configure(
        DEBUG=True,
        DATABASES={
            DEFAULT_DB_ALIAS: {
                'ENGINE': 'django.db.backends.sqlite3',
                'NAME': DB_FILE}},
        LOGGING={'version': 1,
                 'disable_existing_loggers': False,
                 'formatters': {
                    'debug': {
                        'format': '%(asctime)s[%(levelname)s]'
                                  '%(name)s.%(funcName)s(): %(message)s',
                        'datefmt': '%Y-%m-%d %H:%M:%S'}},
                 'handlers': {
                    'console': {
                        'level': 'DEBUG',
                        'class': 'logging.StreamHandler',
                        'formatter': 'debug'}},
                 'root': {
                    'handlers': ['console'],
                    'level': 'WARN'},
                 'loggers': {
                    "django.db": {"level": "WARN"}}})
    app_config = AppConfig(NAME, sys.modules['__main__'])
    apps.populate([app_config])
    django.setup()
    original_new_func = ModelBase.__new__

    @staticmethod
    def patched_new(cls, name, bases, attrs):
        if 'Meta' not in attrs:
            class Meta:
                app_label = NAME
            attrs['Meta'] = Meta
        return original_new_func(cls, name, bases, attrs)
    ModelBase.__new__ = patched_new


def syncdb(model):
    """ Standard syncdb expects models to be in reliable locations.

    Based on https://github.com/django/django/blob/1.9.3
    /django/core/management/commands/migrate.py#L285
    """
    connection = connections[DEFAULT_DB_ALIAS]
    with connection.schema_editor() as editor:
        editor.create_model(model)

main()