title: SQLAlchemy 'Comparator' object has no attribute 'has_key'
body: <p>I am working with JSON SQLAlchemy column and my query statement needs the 'has_key' attribute, but apparently my 'Comparator' object doesn't have this attribute. </p>
  
  <pre><code>Transaction.query.filter(Transaction.fields.has_key('issuername')).all()
  </code></pre>
  
  <p>where Transaction.fields is a Column(JSON). I get error "AttributeError: Neither 'InstrumentedAttribute' object nor 'Comparator' object associated with Transaction.fields has an attribute 'has_key'". My SQLAlchemy is latest version 1.09. Am I building this query wrong? </p>