Django model 外键 xx_id field

子model:portrait/ability_score/views.py

from django.db import models


# Create your models here.
class AbilityScore(models.Model):
    index = models.AutoField(db_column="Index", auto_created=True, primary_key=True)
    employee_id = models.CharField(db_column="EmployeeID", max_length=10, default='')
    ability = models.ForeignKey(to='ability_standard.AbilityStandard', on_delete=models.CASCADE,
                                db_column="AbilityID", default=None)
    approved_value = models.CharField(db_column="ApprovedValue", max_length=2, default='')
    upcoming_value = models.CharField(db_column="UpcomingValue", max_length=2, default='')
    create_time = models.DateTimeField(db_column="CreateTime", auto_now_add=True)
    update_time = models.DateTimeField(db_column="UpdateTime", auto_now=True)

    class Meta:
        managed = True
        db_table = 'ability_score'
        constraints = [
            models.UniqueConstraint(fields=['employee_id', 'ability_id'], name='unique_employee_id_ability_id')
        ]

子表：ability_score

父model:portrait/ability_standard/models.py

from django.db import models

# Create your models here.
class AbilityStandard(models.Model):
    ability_id = models.BigAutoField(db_column='AbilityID', primary_key=True)  # Field name made lowercase.
    department = models.CharField(db_column='Department', max_length=50,default='',
                              db_comment='部门')  # Field name made lowercase.
    ......

注意点：

• 通过ability = models.ForeignKey(to='ability_standard.AbilityStandard', on_delete=models.CASCADE, db_column="AbilityID", default=None)创建外键时会自动生成一个ability_id的属性。

  • 子model里ability属性实质是父model AblityStandard的对象
  • 子model 里ability_id属性是int和父model主键ability_id保持一致。
  • 子表ability_score里AilityID列是子model的ablity_id属性的值和父model主键ability_id保持一致。
  • ability(外键&父model对象)衍生出ability_id(属性&int) 和AilityID(列名)
  • ability_id虽然在子类AbilityScore里明面代码上没有，实际上是存在的，所以在设唯一约束models.UniqueConstraint(fields=['employee_id', 'ability_id'] name='unique_employee_id_ability_id')时可以直接使用而不报错,具体见下图debug信息。
  • 

• models.ForeignKey()函数的to指定app.model_name (ability_standard.AbilityStandard)

• 引用时不需要import ability_standard ,Django 自动找。

• 指定了model_name后通过子表外键(ability = models.ForeignKey)关联了父表的主键(ability_id = models.BigAutoField(db_column='AbilityID', primary_key=True))。这时子表的外键(ablitity)实际上时是父表的model的一个对象，因此可以如下直接通过子表外键获取父表属性：其中ability是子表外键，department是父表的属性。

  employee_score.ability.department

• 建立外键时默认为子表添加了一个属性名_id的字段，可单独指定列名db_column，需要给defualt值。