ruby on rails - What exactly is the difference between has_many, has_and_belongs_to_many and embeds_many in mongoid? -

i understand not programming problem, unable find clear , descriptive solution.

mongoid's documentation quite clear:

embedded relations describe documents stored inside other documents in database.

referenced relations describe documents reference documents in collection storing foreign key data (usually id) other document in itself.

in detail:

referenced 1-n / has_many

when defining relation of nature, each document stored in respective collection, child document contains "foreign key" reference parent.

# parent band document. { "_id" : objectid("4d3ed089fb60ab534684b7e9") }  # child member document. {   "_id" : objectid("4d3ed089fb60ab534684b7f1"),   "band_id" : objectid("4d3ed089fb60ab534684b7e9") } 

referenced n-n / has_and_belongs_to_many

when defining relation of nature, each document stored in respective collection, , each document contains "foreign key" reference other in form of array.

# band document. {   "_id" : objectid("4d3ed089fb60ab534684b7e9"),   "tag_ids" : [ objectid("4d3ed089fb60ab534684b7f2") ] }  # tag document. {   "_id" : objectid("4d3ed089fb60ab534684b7f2"),   "band_ids" : [ objectid("4d3ed089fb60ab534684b7e9") ] } 

embedded 1-n / embeds_many

documents embedded using embeds_many macro stored array of hashes inside parent in parent's database collection.

{   "_id" : objectid("4d3ed089fb60ab534684b7e9"),   "albums" : [     {       "_id" : objectid("4d3ed089fb60ab534684b7e0"),       "name" : "violator",     }   ] }