can an entity have attributes with a different namespace? [<e-id> <attribute> ...] [1 :person/name] [1 :movie/title]

does the "/" in attribute carry any meaning?

I started getting strange error while deleting entity. Message says

"java.lang.IllegalArgumentException: :db.error/reset-tx-instant You can set :db/txInstant only on the current transaction.”

(defn delete-entity [conn entity-id person-id]
  (t/info "delete-entity" entity-id person-id)
  (d/transact conn [[:db.fn/retractEntity entity-id]]))

@drewverlee yes, an entity can have attributes from multiple namespaces, it has no special meaning

namespaces do help keep things organised so I’d recommend you don’t mix them

Does anyone know if there’s a way for a database function to return/execute multiple transactions?

I’m doing a data migration in a database function and it needs to do a :db/add for the entity and have a transaction

so (datomic/transact conn [[:db/add id :attribute value]{:db/id #db/id[:db.part/tx] :tx-attribute value2}]) for each entity

Is there a way of running a 'migration function', with either vanilla datomic or conformity? In conformity you might add a migration that says all my users have :user/first-name attributes. But what is the best way to then iterate over all my users and transact that new data for each user?

@mbutler I've needed a "data migration" like that as well

I'd just build my own "migrate" tool that does both schema migrations and data migrations

no need to make a transactor fn for that IMO

@pesterhazy Thanks, that does appear the best answer atm. If anyone else has some experience of this let me know 🙂

@podviaznikov Can you provide more info about the entity ID you’re passing to the function? I would expect that error if, for instance, you tried to call retractEntity on a transaction eid

@mbutler I do this all the time with sql migrations - I don't like any of the existing frameworks and it's so simple to build

Datomic 0.9.5554 is now available https://groups.google.com/d/topic/datomic/d74excL8JaI/discussion

is it possible to use datalog without datomic?

@marshall I’ll double check if it was regular entity id. I think it was, but will check. Thanks!

hi, can I get an enlightenment how datomic sends and receives data (esp. does it store data or is just a layer to a database)? for example, my old understanding of Client-Server is: Client (e.g. mobile) -> sends data (e.g. JSON) over HTTP -> Server (e.g. Liberator/Pedestal?) -> stores it to Database (e.g. Datomic) ... is this wrong? or something is missing in the flow?

In datomic, there are three concepts: storage, transactor, peer

storage is where all the data is, mostly key-value of blob values

peers read out of storage directly

in storage is the address of a transactor (which is the only process allowed to write to storage)

peers see this address and connect to a transactor. The transactor gives peers a live stream of writes to datomic (the tx-queue), and also accepts transactions to write.

@ejelome That is a rough summary of datomic's system architecture

hey, awesome summary @favila, so in that case, datomic has its own storage

@ejelome well, it has its own expectation for how its keys and values are laid out, but it does not have its own storage service

@ejelome it is parasitic on some other tech for storage, e.g. dynamodb, a sql database, cassandra, etc

but the only thing it needs is transactional update, blob storage, and retrieval by a key

the dev/free transactor uses an embedded h2 database (sql)

ahhh, so it just says how to store and retrieve data but the actual storage is a separate layer

not only storage but networked retrieval

e.g. if storage is sql, peers make a sql query (select * from datomic_kvs where id="xxx") against storage to perform "reads"

transactors use an insert/update to perform writes

oh, so it kind of has pre-made way to deal with kind of database you'll store/retrieve the data

It's not something you control

I would assume it's differently handled on diff databases, e.g. rdbms is diff. to nosql is diff. to <insert another kind of db>

yes, that is true. but they're all used as key-value stores, there's not that much difference

ok, now I understand better, but I want to ask two more important questions

? <-> datomic <-> ?

basically, the in between

http://docs.datomic.com/architecture.html

Are you aware of the diagram on this page?

oh, no XD

wait a sec I'll read

great! this answered one of the two question (storage): http://docs.datomic.com/storage.html#outline-container-1

it's a bit daunting to understand tbh

so then, knowing that it just provisions a database, does datomic also need some sort of way to handle incoming traffic? e.g. liberator/pedestal?

or i can handle it on its own

what kind of traffic?

looking at the chart: app <-> client <-> http+transit <-> server the client is liberator/pedestal?

no

these are the arch of datomic itself

everything else is in the circle "App"

that's where your code is that "uses" datomic as a db and which doesn't care about datomic's arch

I'm actually confused with the app and client because I usually think of the app as the client itself

e.g. if you have a traditional CRUD webapp, you have client, server, and db. swap out DB with something else (e.g. mysql vs datomic), the arch remains the same

Your web server is a client to the db

the browser is a client to the web server

"client" and "server" are relative/relational, not absolute terms

where the "client" is depends on your perspective

so something like: cljs <-> liberator/pedestal <-> datomic

for a full web app, sure

sorry favilla, too dumb about this stack

js/html <-> php <-> mysql is an exact analogy

there are two clients and two servers

oh, I was limiting myself with the jargon (e.g. client as strictly front-end), that's why

ok, going with the big picture: client 1: app (cljs) <-> client 2: server (liberator/pedestal) <-> db (datomic)

oh nevermind, I'm crammed up

that should be better I think

hey @favila, thanks for the patience, really appreciate it, a bit slow to learn the architecture and its flow but I'm finally getting it, have a good dawn 😄