:db.fn/call behavior

[souenzzo]

On datomic, when we call a "transaction function", the db that this function receive is the db before all transaction

In datascript 1.0.1, it receive a "partial db" relative to it's position in transaction

This behavior should be documented ?!

(let [conn (ds/create-conn)]
  (ds/transact! conn [[:db.fn/call println]
                      {:a 42}
                      [:db.fn/call println]
                      {:b 24}
                      [:db.fn/call println]]))
=>
#datascript/DB {:schema nil, :datoms []}
#datascript/DB {:schema nil, :datoms [[1 :a 42 536870913]]}
#datascript/DB {:schema nil, :datoms [[1 :a 42 536870913] [2 :b 24 536870913]]}

[tonsky]

Yes. Are you willing to provide a PR for e.g. README.md?

[refset]

Just an FYI that the Datomic Jepsen report discusses this distinction, and Stu elaborated on the reasoning here: https://news.ycombinator.com/item?id=40373311

It is worth noting here that Datomic's intra-transaction semantics are not a decision made in isolation, they emerge naturally from the information model.
Everything in a Datomic transaction happens atomically at a single point in time. Datomic transactions are totally ordered, and this ordering is visible via the time t shared by every datom in the transaction. These properties vastly simplify reasoning about time.
With this information model intermediate database states are inexpressible. Intermediate states cannot all have the same t, because they did not happen at the same time. And they cannot have different ts, as they are part the same transaction.