Django唯一约束在foring键上失败

Question

我的Django数据库（SQLite）上有两个表，一个是研究和会议领域。会议有三个外键与研究领域的主键相关。在migrate命令期间，我填充数据库（从csv文件读取），但是当插入两个具有相同外键值（对于所有三个键）的会议时，将显示唯一约束failed。 如果我使用admin页面插入Conferences，数据库会给出相同的错误。 我怎样才能解决这个问题

model.py

class Field_Of_Research (models.Model):
     for_id = models.PositiveIntegerField(primary_key=True)
     name = models.CharField(max_length=256)

def __str__(self):
    return self.name

class Conference (models.Model):
    conf_id = models.PositiveIntegerField(primary_key=True)
    title = models.CharField(max_length=256)
    primary_for = models.ForeignKey(to=Field_Of_Research, default=0, on_delete=models.SET_DEFAULT, related_name= 'primary_for')
    secondary_for = models.ForeignKey(to=Field_Of_Research, default=0, on_delete=models.SET_DEFAULT, related_name= 'secondary_for')
    third_for = models.ForeignKey(to=Field_Of_Research , default=0, on_delete=models.SET_DEFAULT, related_name= 'third_for')

def __str__(self):
    return self.title

填充.py

with open('./server/api/database/files/fields_of_research.csv') as csv_file:
    csv_reader = csv.reader(csv_file, delimiter=';')
    for row in csv_reader:
        f=Field_Of_Research.objects.get_or_create(
            for_id = row[0],
            name = row[1]
        )
    print(f'Fields of Research done.')
#Populates the conferences database
with open('./server/api/database/files/conferences.csv') as csv_file:
    csv_reader = csv.reader(csv_file, delimiter=';')
    for row in csv_reader:
        print(row)
        c=Conference.objects.get_or_create(
            conf_id = row[0],
            title = row[1],
            primary_for = Field_Of_Research.objects.get(for_id=int(row[3])),
            secondary_for = Field_Of_Research.objects.get(for_id=int(row[4])),
            third_for = Field_Of_Research.objects.get(for_id=int(row[5])),
        )
    print(f'Conferences done.')

错误

  File "C:\Users\andre\AppData\Local\Programs\Python\Python38-32\lib\site-packages\django\db\backends\utils.py", line 86, in _execute
return self.cursor.execute(sql, params)
  File "C:\Users\andre\AppData\Local\Programs\Python\Python38-32\lib\site-packages\django\db\backends\sqlite3\base.py", line 396, in execute
return Database.Cursor.execute(self, query, params)
  sqlite3.IntegrityError: UNIQUE constraint failed: api_conference.third_for_id