title: How to judge if an element is in list as defined Jsonfield?
body: <p>I use peewee related with an exsits table:</p>
  
  <pre><code>import peewee
  from playhouse.postgres_ext import *
  class Rules(peewee.Model):
      channels = JSONField(null=True)
      remark = peewee.CharField(max_length=500,  null=True)
      class Meta:
          database = db
          db_table = 'biz_rule'
          schema = 'opr'
  </code></pre>
  
  <p>example: in my table there exists a record in column channels:</p>
  
  <pre><code>["A012102","C012102","D012102","E012102"]
  </code></pre>
  
  <p>I want to judge whether "A012102" is in the list,how to write the code?</p>