EntityId (to replace Id.*)

Issues with Id.*, ProgramType, and ElementType (cdap-cli)

• Id.*
  • toString() is inconsistent
  • JSON serialization is inconsistent (since sometimes we use NamespacedIdCodec and sometimes we don't)
  • Doesn't look pretty in JSON form due to heavy nesting
  • Needs lots of extra code to implement JSON codec (NamespacedIdCodec)
  • Id.Program vs Id.Flow: two classes that do the same thing
  • Constructing an Id.* is requires repetition
• ProgramType
  • Inconsistent in JSON form compared to other CDAP entities (using "Flow", "Mapreduce", etc. form instead of "flow", "mapreduce", etc. form to maintain backwards-compatibility)
  • SchedulableProgramType duplicates ProgramType
• ElementType
  • Only in cdap-cli
  • Doesn't cover every type of entity

Proposal

• EntityType: enum that describes every type of entity in CDAP (namespace, application, program, program run, flowlet, flowlet queue, schedule, notification feed, artifact, system service, etc.)
• EntityId: base class for entities in CDAP
  • No nesting
  • Consistent "static EntityId fromString(String)" and "String toString()"
  • Consistent JSON serialization and deserialization (still need custom deserializer, but it should have much less code than NamespacedIdCodec, and should support all EntityIds)

Examples

• toString() 

  namespace:foo
  artifact:foo.art.1.2.3
  dataset:foo.zoo
  dataset_module:foo.moo
  dataset_type:foo.typ
  stream:foo.t
  application:foo.app
  program:foo.app.flow.flo
  program_run:foo.app.flow.flo.run1
  flowlet:foo.app.flo.flol
  flowlet_queue:foo.app.flo.flol.q

• GSON.toJson()

  {"namespace":"foo","entity":"NAMESPACE"}
  {"namespace":"foo","artifact":"art","version":"1.2.3","entity":"ARTIFACT"}
  {"namespace":"foo","dataset":"zoo","entity":"DATASET"}
  {"namespace":"foo","module":"moo","entity":"DATASET_MODULE"}
  {"namespace":"foo","type":"typ","entity":"DATASET_TYPE"}
  {"namespace":"foo","stream":"t","entity":"STREAM"}
  {"namespace":"foo","application":"app","entity":"APPLICATION"}
  {"namespace":"foo","application":"app","type":"Flow","program":"flo","entity":"PROGRAM"}
  {"namespace":"foo","application":"app","type":"Flow","program":"flo","run":"run1","entity":"PROGRAM_RUN"}
  {"namespace":"foo","application":"app","flow":"flo","flowlet":"flol","entity":"FLOWLET"}
  {"namespace":"foo","application":"app","flow":"flo","flowlet":"flol","queue":"q","entity":"FLOWLET_QUEUE"}