Q:

Hyperledger Composer Playground Query

Can we query using the Hyperledger Composer Playground or can we only query using the REST API? I read the tutorial, but it only shows how to query using the REST API.

A:

as Pronoy says, you can use REST APIs. Alternative is to set up a transaction, that calls a defined query (in queries,qry) - purely for testing and logging messages etc. Eg. 
return query('selectPerson', {firstName: 'joe'} )
    .then(function (results) {

       for (var n = 0; n < results.length; n++) {
               var person = results[n];
               console.log('person is ' + (n+1) + ', object is ' +  person);
               console.log('person identifier is ' + person.getIdentifier());

         return personRegistry.get(person.getIdentifier())
         .then(function (personRecord) {
            console.log('object is ' + personRecord); // all good
           console.log('identifier is ' + person.getIdentifier() );
         })

       } // for

  }) //function

