python - 将默认值设置为 django 中两个不同字段的组合

Question

我正在学习 Django，并为自己学习了一个项目，一个费用管理器......下面是我的代码:

from __future__ import unicode_literals
from django.core.validators import RegexValidator

from django.db import models

# Create your models here.

class Person(models.Model):
    first_name= models.CharField(max_length=15)
    last_name= models.CharField(max_length=15)
    email=models.EmailField(blank=True, verbose_name="E-Mail")
    city= models.CharField(max_length=25)
    state= models.CharField(max_length=30)
    phone_number= models.CharField(max_length=10, validators=[RegexValidator(r'^\d{1,10}$')])

    def __unicode__(self):
        return self.first_name

class Data(models.Model):
    borrower_name= models.ForeignKey(Person, related_name="the_borrower")
    lender_name= models.ForeignKey(Person, related_name="the_lender")
    info= models.CharField(max_length=1000, default="Borrower from Lender")
    witness_name= models.ForeignKey(Person, related_name="the_witness")
    money_lended= models.IntegerField()
    date= models.DateField(null=True)

    class Meta:
        verbose_name_plural = "Data"

    def __unicode__(self):
        return self.info

class Log(models.Model):
    log= models.ForeignKey(Data)
    status= models.CharField(max_length=15)
    date= models.DateField(null=True)

    def __unicode__(self):
        return self.status

我想要做的是，在class Data中，我想将info值设置为borrower_name和的组合贷方名称...

例如:
borrower_name=“SHUBHANK”
lender_name=“SAMEER”
那么 info 的值应该是

SHUBHANK from SAMEER

但是当我输入如下代码时:

class Data(models.Model):
    ...
    ...
    info= borrower_name + " from " + lender_name
    ...
    ...
    ...
    def __Unicode__(self):
        return self.info

错误是这样的:

TypeError: unsupported operand type(s) for +: 'ForeignKey' and 'unicode'

帮我摆脱这个!提前致谢!

Answer 1

使 info 成为属性或方法

@property
def info(self):
    return "{} from {}".format(self.borrower_name, self.lender_name)

您将无法在任何查询中使用它，但从您显示的方式来看，我认为您根本不需要这样做。