this is probably a silly question but if I have a fn that transacts, then derefs the future of the transaction, and then calls datomic.api/db on the db connection, is that call to datomic.api/db guaranteed to reflect a db value consistent with the tx, or would I need to use the db-after from the transaction to ensure the tx is reflected in the db value? for instance (defn test-tx [tx-data] @(d/transact (:conn db) tx-data) (d/db (:conn db)))

I generally use db-after, but wondering if that is strictly necessary

Db-after is the db immediately after the tx. D/db is some db after the tx (could possibly be after other later txs). The fact that the deref completed means that tx is now visible to the peer and any d/db on that peer will now include it @djjolicoeur

@djjolicoeur assuming the txn is successful. If it fails or times out your call to d/db might still succeed (depending on how you handle, or don't handle, the failure)

Timed out or failed txn will throw when you dereference the future http://docs.datomic.com/clojure/#datomic.api/transact

thanks @favila @marshall wasn’t sure, assuming a successful tx, whether the the peer was guaranteed to reflect that tx when a value was requested. I generally use db-after anyways to isolate from other tx’s in the system anyways, but we were having a discussion in the office today and I wasn’t sure on whether it was strictly necessary.

https://github.com/Datomic/day-of-datomic/blob/master/tutorial/schema_queries.clj#L18-L20 :db/id doesn't show up in this query, is it considered "special"?

@dominicm You mean in the result of this query? Yes, there is no such attribute, it's just the e in the eavt indices.

@dominicm Also count an entity, and you won't see ;db/id counted, or seq it. It's a special field in the entity.

hi all , is it possible to rename a field when using the pull api , i am fetching deeply nested data and would like to alias it , the nested value is returned something like {:person {:company {:location "somewhere}}} , when accessing the pull'd data i would prefer to access person-location instead of (:location (:company (:person data))) , hope that makes sense

@rc1140 pull can only do two transformations: limit cardinality-many results, and default cardinality-one values

thanks , saw that in the docs , just wanted to make sure didnt miss something obvious

@rc1140 you can assert :person-location as another ident for the same attribute

that may work

but it's a really bad idea

not sure i follow what you mean ?

when you assign an ident, the old ident still works

(until the old ident is assigned to something else)

right , i get why that would be a bad idea as well , im happy doing a long form extraction out of the map for now

ah, nevermind, I misunderstood the transform you want

you actually want to collapse levels

correct

using threading makes it a little less painful atm

If you are unfamiliar with the clojure.,walk namespace, it is very handy for post-processing pull expression results

not familiar with it , but will go read up on it , any links you have on hand that you think would be a good intro

just the docs: https://clojure.github.io/clojure/clojure.walk-api.html

An example: https://gist.github.com/favila/6366516f2bef6b77b07f7349d4ff009e

ta

wow

have never seen that style of using the pull api before

?

using d/pull and then passing it to the walk stuff , i have only using the pull api by calling d/q and then passing in i a query vector

oh

vague question here. using the tx-pipeline from best practices (http://docs.datomic.com/best-practices.html#pipeline-transactions) i’m getting clojure.lang.PersistentArrayMap cannot be cast to java.util.List. I can see that I’m passing a map to transactAsync within the pipeline, but I would expect that to work. Does this sound familiar to anyone?

nvm. I see what I did wrong !

transactions can never be maps

an item in a transaction can be a map

yeah, I’m wishing I would delete that embarrassing question … but it’s good to humble oneself periodically

Hi, there is some way to same datomic's :db/txInstant in other atribute? (Example: I want to save {:db/id (d/tempid :db.part/user) :msg/txt "Hello" :msg/inst <#C03RZMDSH|datomic>/inst})

Yes, I now that I can make a query where [?msg-id :msg/txt _ ?tx][?tx :db/txInstant ?v], but it's the only way?

@souenzzo You can't know the time a transaction completes until it completes?

You can get the current datomic t value (before your transaction) by calling (d/basis-t db)

...which would give you "transaction before this one" as a potential (d/as-of) target for historical data

(Assuming that no other new data is transacted from a different process in between the time your call to (d/db conn) completes and when your {:msg/txt "Hello"} transaction completes)

(clj-time.core/now) will do for now

🙂

Good idea 😉