In Datomic, how do I get a timeline view of the changes made to the values of a particular entity?

clojure, datomic

Solution

Take a look at the `(history db)` function in the reference.

Returns a special database containing all assertions and retractions across time. This special database can be used for datoms and index-range calls and queries, but not for entity or with calls. as-of and since bounds are also supported. Note that queries will get all of the additions and retractions, which can be distinguished by the fifth datom field :added (true for add/assert) [e a v tx added]

Using `history` you can do something like this to get the data you wanted:

datomic-test.core> (q '[:find ?tx ?tx-time ?v 
                        :in $ ?e ?a 
                        :where [?e ?a ?v ?tx _] 
                               [?tx :db/txInstant ?tx-time]] 
                      (d/history (db conn)) 
                      2000 
                      :db/doc)
#<HashSet [[13194139534315 #inst "2012-09-09T00:45:49.086-00:00" "Hello There"] [...]]>

Also look at `(tempid :db.part/user)` to get IDs instead of using hard coded numbers like `2000`.

Problem

I'm following the tutorial, http://www.datomic.com/company/resources/tutorial but I think I am missing a simple piece of the puzzle of how to access Datomic's time model. If I do a series of adds and retracts ``` ;; DO a series of transactions ;; (transact conn [:db/add entity-id attribute value0]) (use 'datomic.api) (dir datomic.api) (def conn (connect "datomic:dev://localhost:4334/demo")) (transact conn '[:db/add 2000 :db/doc "Hello There"]) (q '[:find ?e ?n :where [?e :db/doc ?n] [(= 2000 ?e)]] (db conn)) ; => <HashSet [[2000 "Hello There"]]> (transact conn '[:db/add 2000 :db/doc "Hello There 1"]) (q '[:find ?e ?n :where [?e :db/doc ?n] [(= 2000 ?e)]] (db conn)) ; => <HashSet [[2000 "Hello There 1"]]> (transact conn '[:db/add 2000 :db/doc "Hello There 2"]) (q '[:find ?e ?n :where [?e :db/doc ?n] [(= 2000 ?e)]] (db conn)) ; => <HashSet [[2000 "Hello There 2"]]> (transact conn '[:db/add 2000 :db/doc "Hello There 3"]) (q '[:find ?e ?n :where [?e :db/doc ?n] [(= 2000 ?e)]] (db conn)) ; => <HashSet [[2000 "Hello There 3"]]> ``` How is it possible to get a series of changes of the value on (entity 2000 attribute :db/doc)? I want to get something in the format of ``` [ [Transaction Number, Time, Value] .... [Transaction Number, Time, Value]] ``` For example: ``` [ [T1, "2012-March-16-9:30:12", "Hello There"] .... .... .... [T27, "2012-June-14-9:54:38", "Hello There 3"] ] ``` It can't be that difficult, but there are a lot of :db internal parameters that I'm not familiar with.

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