Clojurians Log v2

LOL! Sounds like me... I've been meaning to learn Datomic for "ages" but now that dev-local is available, I think I actually might.

I'm not yet at the stage of working with anything that complex, but so far I'm very happy, probably just because it all makes so much sense ...

How can I move the identity :test/id from the entity 17592186045418 to the new entity (referenced by :test/ref). Do I have to do this in two separate transactions? All I want to do is move the identity to a new entity in a single transaction. I understand why the temp ID resolution is taking place and resolving the temp ID to a conflict but how can I avoid it. How can I force a new entity here?

Interesting problem! I'm interested to see the solution for this.. I expect you'd have to split to two transactions since you're working with db.unique/identity though

Yeah. That's what I did. I don't like it because now there's a point in time where the database sort of has an inconsistent state. It's not the end of the world but I really want it to commit as a single transaction. For this to actually go though, the transactor, would have to somehow react to the fact that the identity is being retracted during the transaction and because of that, it mustn't be allowed to partake in temp ID resolution. (either that, or you tag the temp ID as unresolvable to force a new entity...)

it seems like a modelling problem if you need to get to a state where an entity has an 'identity', then loses it and gives it to another entity - so I could see why this could be unsupported behaviour

I'm fixing a data problem or rather I'm doing this because I'm revising the data model. I ran into this as part of a upgrade script I wrote.

I know Marshal has commented in the past on some of these transactional isolation behaviours. As to why it might need to work this way but I'm curious to what the reasoning for it is. As I can see a way to program around it but I can also understand that you might not want to just do that.

You could argue that I'm https://blog.datomic.com/2017/01/the-ten-rules-of-schema-growth.html or some such.

I suspect that it's a bit of a trade-off - if you have this behaviour, it's simpler to reason about transactions, since it's likely implemented in a ref-resolution phase, then an actual write phase

but if you have clever transactions where you effectively mutate the state for each fact, then things get trickier to accurately reason about

I had this kind of issue for new schema, and schema that used the new schema:

[{:db/ident :ent/displayname}
 {:db/ident :ent/something
  :ent/displayname "Hello"}]

so I had to write a function that checks existence of the properties and then split the schema assertion into multiple phases

Yeah, so this rule applies to attributes. Which I sort of understand. You cannot refer to schema before it exists but for data though. Are the same constraints equally valid?

Hello, I'm new to Clojure and Datomic. I'm using the min aggregate to find the lowest-priced product, but can't seem to figure out how to get the entity ID of the product along with it -

;; schema
(def product-offer-schema
  [{:db/ident :product-offer/product
    :db/valueType :db.type/ref
    :db/cardinality :db.cardinality/one}
   {:db/ident :product-offer/vendor
    :db/valueType :db.type/ref
    :db/cardinality :db.cardinality/one}
   {:db/ident :product-offer/price
    :db/valueType :db.type/long
    :db/cardinality :db.cardinality/one}
   {:db/ident :product-offer/stock-quantity
    :db/valueType :db.type/long
    :db/cardinality :db.cardinality/one}
  ])
(d/transact conn product-offer-schema)

;; add data
(d/transact conn
  [{:db/ident :vendor/Alice}
   {:db/ident :vendor/Bob}
   {:db/ident :product/BunnyBoots}
   {:db/ident :product/Gum}
  ])
(d/transact conn
  [{:product-offer/vendor  :vendor/Alice
    :product-offer/product :product/BunnyBoots
    :product-offer/price   9981 ;; $99.81
    :product-offer/stock-quantity 78
   }
   {:product-offer/vendor  :vendor/Alice
    :product-offer/product :product/Gum
    :product-offer/price   200 ;; $2.00
    :product-offer/stock-quantity 500
   }
   {:product-offer/vendor  :vendor/Bob
    :product-offer/product :product/BunnyBoots
    :product-offer/price   9000 ;; $90.00
    :product-offer/stock-quantity 15
   }
  ])

;; This returns the lowest price for bunny boots as expected, $90:
(def cheapest-boots-q '[:find (min ?p) .
                        :where
                        [?e :product-offer/product :product/BunnyBoots]
                        [?e :product-offer/price ?p]
                       ])
(d/q cheapest-boots-q db)
;; => 9000

;; However I also need the entity ID for the lowest-priced offer, and
;; when I try adding it, I get the $99.81 boots:
(def cheapest-boots-q '[:find [?e (min ?p)]
                        :where
                        [?e :product-offer/product :product/BunnyBoots]
                        [?e :product-offer/price ?p]
                       ])
(d/q cheapest-boots-q db)
;; => [17592186045423 9981]

datalog doesn’t support this kind of aggregation (neither does sql!)

you can do this with a subquery that finds the max, then find the e with a matching max in the outer query; or, do it in clojure

:find ?e ?p then (apply max-key peek results) (for example)

the reason datalog and sql don’t do this is because the aggregation is uncorrelated: suppose multiple ?e values have the same max value: which ?e is selected? the aggregation demands only one row for the grouping

(you still have that problem BTW--you may need to add some other selection criteria)

Ah I see, thank you!

Hello I am playing with dev-local datomic. When I try to create a database I get error.

java.nio.file.NoSuchFileException: "/resources/dev/quizzer/db.log"
....

(ns quizzer.core
  (:require
   [datomic.client.api :as d]))

(def client (d/client {:server-type :dev-local
                       :storage-dir "/resources"
                       :system "dev"}))

;; Creating a database
(defn make-conn [db-name]
  (d/create-database client {:db-name db-name})
  (d/connect client {:db-name db-name}))

(comment
  (d/create-database client {:db-name "quizzer"}))

does /resources/dev/quizzer exist?

or more simply, does /resources exist?

I placed it in the root directory. Here is project structure

.
├── README.md
├── deps.edn
├── resources
│   └── dev
│       └── quizzer
│           └── db.log
├── src
│   └── quizzer
│       └── core.clj
└── test
    └── quizzer
        └── core_test.clj

7 directories, 5 files

And the deps.edn structure

{:paths ["src" "resources" "test"]
 :deps {org.clojure/clojure              {:mvn/version "1.10.1"}
        com.datomic/dev-local            {:mvn/version "0.9.195"}}
 :aliases {:server {:main-opts ["-m" "quizzer.core"]}
           :test {:extra-paths ["test/quizzer"]
                  :extra-deps  {lambdaisland/kaocha {:mvn/version "0.0-529"}
                                lambdaisland/kaocha-cloverage {:mvn/version "1.0.63"}}
                  :main-opts   ["-m" "kaocha.runner"]}}}

"/resources" is an absolute path

I assume that's in your ~/.datomic/dev-local.edn

Absolute path was the problem, thank you @alexmiller

I have a datomic cloud production topology, which shows the correct number of datoms in the corresponding CloudWatch dashboard panel..... however, the datoms panel for my other solo topology never shows any datoms, no matter how many I transact into the system

I know solo reports a subset of the metrics, but according to https://docs.datomic.com/cloud/operation/monitoring.html#metrics solo should report that datoms metric. > Note In order to reduce cost, the Solo Topology reports only a small subset of the metrics listed above: Alerts, Datoms, HttpEndpointOpsPending, JvmFreeMb, and HttpEndpointThrottled. Not sure what's going on. I'm seeing the same on our solo stacks though @jake.shelby.

Even the solo https://docs.datomic.com/cloud/operation/monitoring.html#dashboardsshows the datoms metric.

thanks for checking your system @kenny, what version is yours? (I just launched mine last week, so it's the latest version

▶ datomic cloud list-systems                                                                                           
[{"name":"core-dev", "storage-cft-version":"704", "topology":"solo"},
 {"name":"core-prod",
  "storage-cft-version":"704",
  "topology":"production"},

Same version

Does anyone have an example on how tx-report-queue is used