Django model中设置多个字段联合唯一约束

1，直接通过 models.ManyToManyField

from django.db import models

class UserInfo(models.Model):    username = models.CharField(max_length=32)    password = models.CharField(max_length=64)

class NewsType(models.Model):    caption = models.CharField(max_length=16)

class News(models.Model):    title = models.CharField(verbose_name=‘标题‘,max_length=32)    url = models.CharField(verbose_name=‘URL‘,max_length=255)    avatar = models.CharField(verbose_name=‘头像‘,max_length=255)    summary = models.CharField(verbose_name=‘简介‘,max_length=255)    new_type = models.ForeignKey(verbose_name=‘新闻类型‘,to="NewsType")    user = models.ForeignKey(verbose_name=‘发布者‘,to=‘UserInfo‘,related_name=‘c‘)    ctime = models.DateTimeField(verbose_name=‘创建时间‘,auto_now_add=True)    like_count = models.IntegerField(default=0)    comment_count = models.IntegerField(default=0)

like = models.ManyToManyField(to=‘UserInfo‘)

class Comment(models.Model):    content = models.CharField(verbose_name=‘评论内容‘,max_length=255)    new = models.ForeignKey(verbose_name=‘评论的新闻ID‘,to=‘News‘)    user = models.ForeignKey(verbose_name=‘评论者‘,to=‘UserInfo‘)    ctime = models.DateTimeField(verbose_name=‘评论时间‘, auto_now_add=True)