Clojurians Log v2

As a noob, ident had my head spinning because everywhere I looked in Datomic I saw IDs. And dto is similar to allegrograph which I grok OK so it is not even alien technology. I guess idents are closest to enum in programmerspeak; they let us give a number a mnemonic (another term I would consider, along with alias). But wait, we are in the Land of Hickey, what does the dictionary say? "name noun 1. a word by which a thing is known, addressed, or referred to." Lovely. Btw, I do not like identifier because the entity-id is an identifier, and the real one needing no translation. Fun stuff. 🙂

Yep. it takes time to learn the language 🙂.

I would be very surprised if it did 🙂 that said, it probably keeps a cache of compiled Datalog queries somewhere in the JVM.

Datomic has a philosophy of "I'm not slowing down because you're watching me", it seems to me that logging every query would go against that philosophy, especially given the aim that most queries be fast walks through in-memory data structures.

seems reasonable. Having that log isn't a goal of mine, if it existed it might be useful though. I'm considering how to extend the datalog language so it could be used across multiple databases. I have no real plans on doing this, just a thought experiment.

It can already do this?

Not sure if you are thinking exactly of this, but you can already supply multiple data sources, :in $ds1 $ds2 then reference in pattern clauses by [$ds1 e-match a-match ...] or in rules by ($ds1 rulename ...)

Not having to mention the default $ name most of the time is syntax sugar

Idents have enough unique properties viz entity ids that it’s worth giving them another name imo. Entity id values are not user-controllable, are not a public contract, and should not be stored durably for long periods outside the system. Idents are all of these, and are also reassignable and guaranteed unique. You can maybe think of them as a special case of lookup ref where the :db/ident attr is implied, although historically lookup refs came later

This May be helpful as a primer on the kinds of “identifying” datomic has: https://docs.datomic.com/on-prem/identity.html

An impl note: at least on on-prem there is a full in-memory map of idents to eids and vice versa, so they are faster forms of reference than normal unique attributes and that is also why you shouldn’t have very large numbers of them

Idents are also valid even after retracted. This is so you can rename an attribute without breaking code—the old name will still work

Thx! I had indeed seen all that. I had not picked up, tho, that idents would work if stored outside the system even when entity-ids had changed. Interesting. But in that same section we see the sentence that actually, I recall, made me stop reading and look for a different tutorial:

When an entity has an ident, you can use that ident in place of the numeric identifier, e.g.

Idents associate a programmatic name (a keyword) with an entity id, by setting a value for the :db/ident attribute

The :db/ident of :db/ident is :db/ident.

There is a really good video on this by folks at nubank. I believe it’s called 4 super powers of Datomic, where they talk about querying across multiple database. Highly recommended

Who do I get a older version of datomic dev-tools ??? My project uses com.datomic/dev-local {:mvn/version "0.9.184"} and I can't find how to download it.

I will look into that -- in the meantime, can you just update the dep to latest. They are all compatible.