clojure - in datomic, how is it possible to find out what keys are available for reverse lookup? -

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the following uses simplified datomic setup:

:account/user -> string :account/email -> ref  :email/name -> string :email/type -> keyword

if have entity containing account information, easy know has email information

(keys <account entity>)  ;; => [:account/user :account/email]  (:account/email <account entity>)  ;; => <email entity>

but on flipside, if @ keys of email entity, not know has linked account information.

(keys <email entity>)  ;; => [:email/name :email/type]  (:account/_email <email entity>)  ;; => <account entity>

how 1 find out :account/_email valid key without trial , error?

to check if key valid can use:

(.containskey <email entity> :account/_email) ;; => true

in order valid entity keys including reverse ones:

(.touch <email entity>) (keys (.cache <email entity>))

note (keys) called directly on entity returns forward keys.

tested on similar schema.

side note: apart 

(:account/_email <email entity>)

you can query accounts have linked specified email:

(q '[:find ?a :in $ ?e :where [?a :account/email ?e] ] (db conn) (:db/id <email entity>))

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