code: function create(body, cb) {
    var validates = Schema(body);
  
    if(!validates) {
      return cb(new exceptions.BadRequest());
    }
  
    db.getClient(function(err, client, done) {
      client.query(INSERT, [body.post_id, body.tag_id], function(err, r) {
        if(err) {
          cb(err);
          done(err);
        } else {
          cb(null, r.rows[0]);
          done();
        }
      });
    });
  }
docs: Creates a Post <-> Tag association
  
  @param {Object} body
  @param {Function} cb