I thought I remembered somewhere in the documentation that you can add a docstring to a transaction. Did I hallucinate that?

Hello! get-else works with cardinality-one attributes only? how can I chek if my cardinality-many attribute has at least one value or not, without disappearing rows with this attr is not setted?

trick with (or [?o :order/my-cardinality-many-attribute ?x] [?o :db/id ?x])works, but it made multiple lines on many values in attribute

@ivana you could use the missing? predicate

Amd a similar or trick

yes, but how can I get all missing and non-missing attr rows just with a chek of missing and without a multiplication lines?

@ivana It's not clear what query you're trying to write. Your or clause above will return all the entities in your database because of [?o :db/id ?x], is it really what you want?

I want simply to check (!) if this entity have at least one value in its card-many attr or not - with the same entity lines as they are.

F.e. I have 2 entities, one with 10 values in many attr, and one with 0. I want 2 rows with bollean flag

Not 11 lines, not 1 line. Just 2 - as a real amount of my entity

There might be a simpler approach but something like this could work:

[:find ?o ?has-many-attr
         :where
         [?o :other/attr]
         (or (and [?o :order/my-cardinality-many-attribute]
                  [(ground true) ?has-many-attr])
             (and [(missing? $ ?o :order/my-cardinality-many-attribute)]
                  [(ground false) ?has-many-attr]))]

thanks, I'l try it

for the first impression it is exactly what I need, thanks alot! I'l play with it in a real queries

Datomic does not accept nil attribute values. If I have an entity

{:foo/id 101
 :foo/code :FOO
 :foo/type "bar"}

(d/transact conn [{:foo/id 101
                   :foo/code :LOL
                   :foo/type nil}])

(d/transact conn [{:foo/id 101
                   :foo/code :LOL}])

You do not need to reassert the whole entity - just retract the part that is no longer true

Without even reading that article it is probably misconceived

yeah it I think misses the point. entities are sets of arbitrarily related attributes, not tables, this takes some getting used to but it’s far more powerful once you get the hang of it. And the example of “So what if we need to set a value to null?“, isn’t really. This

(datomic/q '[:find ?id ?firstname ?lastname
             :in $
             :where
             [?id :user/firstname ?firstname]
             [?id :user/lastname ?lastname]]
           (datomic/db conn))

(datomic/q '[:find ?id (pull ?e [:user/firstname :user/lastname])
             :in $ 
             :where
             [?id :user/firstname]
             ; - or perhaps -
             [?id :user/id]
           ]
           (datomic/db conn))

also, the edit-or-create-user-txnexample seems to conflate empty strings with null/nil. Now that may be desired behavior in certain circumstances, but “” is not nil/null/“not present”, even in a traditional say relational db. Also, figuring out retracts is pretty trivial. a set/difference on the keys of the incoming update and an existing entity will give you that directly. “” as nil, if necessary can be tacked on with filter prior to the diff

Calling cast/even from wihtin CIDE results in a StackOverflowError

Execution error (StackOverflowError) at cider.nrepl.middleware.out/print-stream$fn (out.clj:93). Has anyone else seen this?

Is there a function in the Peer api that allows a user to programmatically determine the transactor’s port?

We are using the map uri, with a cassandra callback, so port is not present in the uri.

(ns bug-demo (:require [datomic.ion.cast :as cast])) (cast/initialize-redirect "/tmp/hamster") (cast/event {:msg "ShouldNotCauseAStackOverflowErrorInCider"})