I finally just got the transactor working. Thanks for your help 🙂

Hi all, I have this existing system that uses a trad ORM with the party model. Party is a base entity that has children of either an Org or a Person. Whats the way to approach such a thing with datomic ?

@len divide the attributes into :party/attributes, :org/attributes and :person/attributes

and then just join them together as needed, seems so simple 🙂

yep, you just get things which have one or more of the attributes you're interested in, you don't have to think in terms of models and inheritance like a trad ORM

I am going through that switch now yip, very elegant

If you’ve got many :refs associated to an attribute, how do you remove one of them from the list?

@zentrope: simply transact a retraction [:db/retract entity-id :my-ref-atrib current-value]

Ah, okay. ;) Hm.

Based on your description i’m assuming it is a cardinality many attribute

that ^ form will retract only the "current-value” ref, but leave the others

Yes, I have something like :product/orders :many. I just want to retract one of those orders.

so, that retraction will retract the reference from your entity to the order.

if you want to retract the whole order entity you’ll need to handle that separately

What’s the current-value in your example?

(No, don’t want to retract the actual order.)

it would be the entity id of the order that is referred to by the reference

so if :product/orders has 3 values, call them A, B, C

and you want to retract the reference to B

you’d put the entity ID of B in for current-value

And a reference to :product/orders’ entity as entity-id.

you might also want to have a look at http://docs.datomic.com/transactions.html#built-in-transaction-functions specifically the retractEntity function - if you ever want to remove the order itself and all references to it

[::db/retract [:product/id “asda”] :product/orders [:order/id “asa”]] <— that sort of thing (pseudocode)?

Okay, I think I got it.

Retract the attribute/value from the entity.

the pseudocode you have there says something along the lines of “i have an entity with :product/id “asda” and it has a bunch of references through the attribute :product/orders. one of those references is to an entity that has the attribute :order/id “asa” and I want to remove that reference from the “asda” entity"

Ok. Thanks.

Hm. Can you actually use [:ns/attr “an-id”] in db/retract?

I’m getting an “invalid lookup ref”.

[:db/retract 277076930200665 :spec/controls [:product/id "a82f5914d899edc259c96303e89133299f14b635”]]

I believe retract requires a value there, not an identity.

You can query for the value first then issue the retraction

You should be ablr to use a lookup ref in the e position however

Hm. I’m getting an “invalid list form” even with proper eids. Must be something else.

Oh, I see. I’m just adding the retract/asserts as a value to an attribute in a map, rather than just concatting them on to the TX itself.

@marshall: Using [:product/id “foo”] inside a [:db/retract] works fine.

Ah. Good deal.

Yeah. Makes sense that it would.

when i try to compile my app, it starts a peer connection and i go over my peer limit. Do people typically have a def like this (def conn (d/connect uri)) or do you set the connection as an atom var on start ?

@jdkealy: the component (Stuart Sierra’s lib) example here is the typical way I see people approach this (also some other good advice in the blog post in general): http://www.rkn.io/2014/12/16/datomic-antipatterns-eager-conn/

datomic newbie here—is there any way for me to introspect into the schema itself?

...assuming that's a meaningful question

Yeah, it's just data and you can query it. https://github.com/Datomic/day-of-datomic/blob/master/tutorial/schema_queries.clj

@bkamphaus: just the sort of thing I was looking for—thanks so much!

im confused about what peers might be connected. is there some way to reset them all ?

Killing the process or calling release for a peer is sufficient, transactor will log all ips connected.