irb(main):008:0> Band.where(x:2).and(Band.where(x:3))
MONGODB | localhost:27741 | mongoid.find | STARTED | {"find"=>"bands", "filter"=>{"x"=>3}, "$clusterTime"=>{"clusterTime"=>#<BSON::Timestamp:0x0000563714d4f070 @seconds=1548439192, @increment=1>, "signature"=>{"hash"=><BSON::Binary:0x47397286344620 type=generic data=0x0000000000000000...>, "keyId"=>0}},...
MONGODB | localhost:27741 | mongoid.find | SUCCEEDED | 0.001s
=> #<Mongoid::Criteria
  selector: {"x"=>2}
  options:  {}
  class:    Band
  embedded: false>

irb(main):009:0> Band.where(x:2).or(Band.where(y:3))
MONGODB | localhost:27741 | mongoid.find | STARTED | {"find"=>"bands", "filter"=>{"y"=>3}, "$clusterTime"=>{"clusterTime"=>#<BSON::Timestamp:0x0000563714d93630 @seconds=1548439212, @increment=1>, "signature"=>{"hash"=><BSON::Binary:0x47397286484620 type=generic data=0x0000000000000000...>, "keyId"=>0}},...
MONGODB | localhost:27741 | mongoid.find | SUCCEEDED | 0.001s
=> #<Mongoid::Criteria
  selector: {"x"=>2}
  options:  {}
  class:    Band
  embedded: false>

irb(main):010:0> Band.where(x:2).where(y:4)
=> #<Mongoid::Criteria
  selector: {"x"=>2, "y"=>4}
  options:  {}
  class:    Band
  embedded: false>

irb(main):011:0> Band.where(x:2).where(x:4)
=> #<Mongoid::Criteria
  selector: {"x"=>4}
  options:  {}
  class:    Band
  embedded: false>