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POUsing a database function in a datomic query
 

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    <p>I'm trying to do an 'outer join' in Datomic via the REST API. From <a href="https://github.com/Datomic/day-of-datomic/blob/master/tutorial/social_news.clj" rel="noreferrer">https://github.com/Datomic/day-of-datomic/blob/master/tutorial/social_news.clj</a> I have taken the final example:</p> <pre class="lang-clj prettyprint-override"><code>(defn maybe "Returns the set of attr for e, or nil if e does not possess any values for attr." [db e attr] (seq (map :a (d/datoms db :eavt e attr)))) ;; find all users (q '[:find ?e ?upvote :where [?e :user/email] [(user/maybe $ ?e :user/upVotes) ?upvote]] (db conn)) </code></pre> <p>I inserted the maybe function into my database, and it can be queried thus:</p> <pre><code>[:find ?n ?v :in $ :where [?e ?a ?v] [?a :db/ident :db/fn] [?e :db/ident ?n]] </code></pre> <p>returns</p> <pre><code>:maybe #db/fn{:code "(seq (map :a (d/datoms db :eavt e attr)))", :params [db e attr], :requires [], :imports [], :lang :clojure} </code></pre> <p>However, I am unable to work out how to call the function in a query. I have an <code>:data/user</code> attribute on some transactions, which I want to get the value for where it exists. Here's the query I'm trying to run; I would like <code>:maybe</code> to be the database function defined above.</p> <pre><code>[:find ?attr ?v ?when ?who :where [17592186045423 ?a ?v ?tx true] [?a :db/ident ?attr] [(:maybe $ ?tx :data/user) ?who] [?tx :db/txInstant ?when]] </code></pre> <p>I'm pretty sure I'm missing something pretty obvious, but I've been stuck on this for a day now. Thanks for any help!</p>
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