OK, so after some more experimentation I found out I needed to do the
get-connection in the prepare-statement instead of the with-db-connection
binding. A bit counter-intuitive, and I hope it will still work when a
connection pool is used.
(j/with-db-connection [c datasource]
(let [ps (j/prepare-statement (j/get-connection c)
"SELECT count(*) from
person where left(name,1)=?")]
(doall (map #(j/query c [ps %])
["a" "b" "c" "d" "e" "f"]))))
On Monday, November 9, 2015 at 11:45:48 AM UTC+1, Niels van Klaveren wrote:
>
> 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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