I’m designing a schema where ordered to-many relationships are a requirement. I’ve seen the various blog posts etc and that seems to suggest either 1/ component wrapper entities with :position attr, 2/ referenced/child entities with :position attribute or 3/ referenced/child entities with linked-list attributes

Does anybody have any experience or war stories from using these various techniques?

Or even better, is there anything on the Datomic roadmap that will help with this?

@steveb8n Datomic can’t really help because it can’t know which of these is most suited to your use-case. few vs many items, items-have-one-parent-list vs items-have-many-parent-lists both have an impact on what you do. by providing for one case, Datomic could mislead people on thinking about these concerns

@steveb8n you should ask on Stackoverflow or the mailing list, and we'll try and give you the tradeoffs

good point. I’m starting to play with this tomorrow so that helps

thanks both, I will post on SO

@val_waeselynck I’ve posted the question. Really appreciate any input. https://stackoverflow.com/questions/44645938/how-to-implemented-sorted-to-many-relationships-in-datomic

Has anyone successfully created a leiningen project with dependencies for both the datomic client and ring? I've found this unresolved issue on SO relating to the exact same problem I have and can't figure out a way around it: https://stackoverflow.com/questions/43291069/lein-ring-server-headless-fails-when-including-datomic-dependency - appears to be caused by ring and the datomic client relying on different but incompatible versions of Jetty?

@shaneprince i had issues with some AWS libs conflicting and had to add ‘[com.amazonaws/aws-java-sdk-dynamodb “1.11.0”]’ by hand to resolve it.

try running lein deps :tree to find offensive lib

in your case try to include a version of jetty that will satisfy different libs

Thanks @karol.adamiec, running lein deps :tree shows the datomic client depends on jetty-util 9.3.7.v20160115 but from my investigation ring core depends on jetty-util 7.6.8.v20121106. I'm on ring 1.6.1 which I believe is the latest version. Is it even possible to include both dependencies that each require different versions of jetty?

dont know… maybe someone else can answer that ;(

For anyone else that comes across this issue: from what I understand it looks like ring-core is using an older jetty adapter for legacy purposes. I've found https://github.com/sunng87/ring-jetty9-adapter a worthy replacement so far.

is the ability to compare datomic :db.type/instant with < documented anywhere?

@matthavener clj-time has comparison functions e.g. https://clj-time.github.io/clj-time/doc/clj-time.core.html#var-latest

@robert-stuttaford i’m more asking if the ability to use a predicate like [(< ?inst1 ?inst2)] is documented

@matthavener and I think that is really odd that inside datalog we can compare #inst, and on clojure not.

all datomic valueTypes must be comparable

otherwise sorted index would be impossible

(except bytes compare on something other than contents? not sure what)

so it's more a clojure "problem", that cant compare #inst, and datomic has a workaround to make it work internally ?

most likely they have a custom comparator for whatever sorted-datom-set data structure they made

the < <= >= > datalog ops are not clojure functions, they are magic

I'm trying to

`[(my-ns/function-that-returns-function ~'?foo) ~bar]
 [(~bar ~'?var1 ~'?var2) ~'?foobar]

what does ~bar expand to?

~'bar both*

com.google.common.util.concurrent.UncheckedExecutionException: java.lang.RuntimeException: Unable to resolve symbol: ?f in this context This is the real exception. The other exception was because I'm using fn(on ~'bar) keyword and it's trying to evaluate a function 😜

`[(my-ns/function-that-returns-function ~'?foo) ~'bar]
 [(~'bar ~'?var1 ~'?var2) ~'?foobar]

`[((my-ns/function-that-returns-function ~'?foo) ~'?var1 ~'?var2) ~'?foobar]

Functions aren't first class inside datalog?

`[(my-ns/function-that-returns-function ~'?foo) ~'?bar]
 [(.invoke ^clojure.lang.Var ~'?bar ~'?var1 ~'?var2) ~'?foobar]