While answering this question
<http://stackoverflow.com/questions/33600132/checking-if-uuid-exists-in-postgresql-table-using-clojure-java-jdbc-db-do-prepar/33605673#33605673>
on stackoverflow about do-prepared I wanted to show the way to do multiple
queries with the same prepared statement (batch select). I thought this is
possible in Java, but in clojure.java.sql I ran into several problems.
Granted that given a properly parameterized query the database should be
able to optimize this automatically by using the execution plan from the
cache, it might give an extra bit of performance by stating it up front.
So I set out to test if that was true, but without much success
Here's my first attempt:
(j/with-db-connection[c datasource]
(let [ps (j/prepare-statement c "SELECT count(*) from person
where left(name,1)=?")]
(doall (map #(j/query c [ps %]) ["a" "b"]))))
ClassCastException clojure.lang.PersistentHashMap cannot be cast to
java.sql.Connection clojure.java.jdbc/prepare-statement (jdbc.clj:454)
This is because prepare-statement seems to expect a true connection, not
the datasource map. All other attempts to wrangle a connection into
with-db-connection ended up in other errors.
(j/with-db-transaction [c (j/get-connection datasource)]
(let [ps (j/prepare-statement c "SELECT count(*) from person
where left(name,1)=?")]
(doall (map #(j/query c [ps %]) ["a" "b"]))))
IllegalArgumentException No implementation of method: :get-level of protocol:
#'clojure.java.jdbc/Connectable found for class:
com.microsoft.sqlserver.jdbc.SQLServerConnection
clojure.core/-cache-protocol-fn (core_deftype.clj:544)
Since query accepts a prepared statement instead of a string, I thought
this should be possible without having to implement a query equivalent of
do-prepared.
Is there something I overlooked ?
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