Can you share the code that is causing that exception @josmith2016?

Here are the lines of code that are causing the issue: (def simpleQuery ["SELECT * FROM table"])

(j/query db2 [simpleQuery]
           {:as-arrays? true})

Ah, you've nested your vectors.

What do you mean?

What you have is equivalent to (j/query db2 [ ["SELECT * FROM table"] ] {:as-arrays? true})

What you want is (j/query db2 ["SELECT * FROM table"] {:as-arrays? true})

You're right

Or, since you have no parameters to your SQL statement, you can omit the brackets altogether: (j/query db2 "SELECT * FROM table" {:as-arrays? true})

(but it's probably better while you're getting used to the library to use a vector, even when there are no parameters, just for consistency)

Lol thanks for the help, sorry it was such a beginner mistake.

No problem! As you said, you're just getting started with Clojure so this sort of thing should be expected -- and we all try to be as helpful and welcoming as we can here!

Would I be able to pm you for these kinds of question? or is it ok to post here?

Probably best to post here -- on the rare off-chance that I'm not actually around 🙂

I have another one, after querying the database I get Exception in thread "main" java.sql.SQLDataException: DATE/TIME value not in standard format.

querying an ingres database

(I'm on Pacific US time and I'm nearly always online -- but I do sleep occasionally and sometimes I even go on vacation!)

I really appreciate all the help. It's been taking me days to figure out simple stuff like this because I didn't realize this group existed until today

OK, so that exception is coming from the JDBC driver itself, not java.jdbc, and I'm not familiar with Ingres (it's not one of the databases I test java.jdbc against).

@josmith2016 I haven't been able to find any information about that exception online...

I haven't either

Are you supplying a date/time value as a string in your query?

No

All it's doing is running that query

There may be null dates / timestamps in the table, would that be an issue?

Hmm, not sure what to suggest -- that exception is coming from the layer below clojure.java.jdbc I suspect (feel free to share the stacktrace as a snippet so I can double-check that).

I would expect null fields to come back into Clojure as nil.

Exception in thread "main" java.sql.SQLDataException: DATE/TIME value not in standard format.
        at com.ingres.gcf.util.SqlExType.getSqlEx(SqlExType.java:99)
        at com.ingres.gcf.util.SqlExFactory.get(SqlExFactory.java:68)
        at com.ingres.gcf.util.IngresDate.getTimestamp(IngresDate.java:1323)
        at com.ingres.gcf.util.IngresDate.getObject(IngresDate.java:1364)
        at com.ingres.gcf.jdbc.JdbcRslt.getObject(JdbcRslt.java:4246)
        at clojure.java.jdbc$dft_read_columns$fn__405.invoke(jdbc.clj:462)
        at clojure.core$mapv$fn__8088.invoke(core.clj:6832)
        at clojure.lang.LongRange.reduce(LongRange.java:233)
        at clojure.core$reduce.invokeStatic(core.clj:6747)
        at clojure.core$mapv.invokeStatic(core.clj:6823)
        at clojure.core$mapv.invoke(core.clj:6823)
        at clojure.java.jdbc$dft_read_columns.invokeStatic(jdbc.clj:462)
        at clojure.java.jdbc$dft_read_columns.invoke(jdbc.clj:458)
        at clojure.java.jdbc$result_set_seq$row_values__415.invoke(jdbc.clj:508)
        at clojure.java.jdbc$result_set_seq$thisfn__417.invoke(jdbc.clj:518)
        at clojure.java.jdbc$result_set_seq$thisfn__417$fn__418.invoke(jdbc.clj:518)
        at clojure.lang.LazySeq.sval(LazySeq.java:40)
        at clojure.lang.LazySeq.seq(LazySeq.java:49)
        at clojure.lang.RT.seq(RT.java:528)
        at clojure.core$seq__5124.invokeStatic(core.clj:137)
        at clojure.core$map$fn__5587.invoke(core.clj:2738)
        at clojure.lang.LazySeq.sval(LazySeq.java:40)
        at clojure.lang.LazySeq.seq(LazySeq.java:49)
        at clojure.lang.Cons.next(Cons.java:39)
        at clojure.lang.RT.next(RT.java:706)
        at clojure.core$next__5108.invokeStatic(core.clj:64)
        at clojure.core$dorun.invokeStatic(core.clj:3134)
        at clojure.core$doall.invokeStatic(core.clj:3140)
        at clojure.core$doall.invoke(core.clj:3140)
        at clojure.java.jdbc$query$fn__543.invoke(jdbc.clj:1098)
        at clojure.java.jdbc$execute_query_with_params.invokeStatic(jdbc.clj:994)
        at clojure.java.jdbc$execute_query_with_params.invoke(jdbc.clj:987)
        at clojure.java.jdbc$db_query_with_resultset_STAR_.invokeStatic(jdbc.clj:1016)
        at clojure.java.jdbc$db_query_with_resultset_STAR_.invoke(jdbc.clj:996)
        at clojure.java.jdbc$query.invokeStatic(jdbc.clj:1090)
        at clojure.java.jdbc$query.invoke(jdbc.clj:1047)
        at clojure.java.jdbc$query.invokeStatic(jdbc.clj:1063)
        at clojure.java.jdbc$query.invoke(jdbc.clj:1047)
        at app.core$_support.invokeStatic(core.clj:49)
        at app.core$_support.invoke(core.clj:40)
        at app.core.support(Unknown Source)
        at app.Application.main(Application.java:17)

Yeah, so that's coming from the .getObject() call on the ResultSet object, before clojure.java.jdbc gets the value.

So I'm going to guess that the Ingres JDBC driver forces you to call a different method for certain SQL data types...

That code is generic in clojure.java.jdbc and works for every database I've encountered so far 😐

I probably have some configuration wrong or something, I'll play around tonight and see what I come up with

Are there other JDBC drivers you could try for Ingres? Maybe some are more "compliant" than others...?

I'll chekc

I only see one on Maven Central: [com.ingres.jdbc/iijdbc "10.2-4.1.10"]

this is the one i'm using com.ingres.jdbc.IngresDriver

It just looked like there were several other options when I searched in general for Ingres JDBC driver.

Do you know which version of the JDBC driver you're using? (from your Gradle build file)

I'm using an older, I'll try updating

compile 'com.ingres.jdbc:iijdbc:10.2-4.1.10'

According to Maven, that's the way to get the latest version in Gradle... (I don't know, I haven't used Gradle for a decade!)

Lol that is the correct syntax

That didn't fix it

I last touched Groovy back in... 2008 I think...

That's along time

What do you use now?

Clojure -- since 2011.

I first learned Clojure in 2010. Went to production on 1.3 Alpha 7 or 8 in 2011. We're on 1.9 in production now.

Nice, this is the first time I've used clojure

My arc was roughly C / assembly / COBOL -> C++ -> Java -> Groovy -> Scala -> Clojure.

I've been a java programmer for like 7 years

I loved Java when I first switched from C++ (around '97)... but got fed up with it by the time Java 5 appeared I think...

I haven't been around for that long but after only seeing java syntax or similar the clojure syntax feels so alien lol it's taking me a while to understand it

For all my backend development I've only used java, besides one time I used c# for a college class

Back at university, I did Lisp, Prolog, APL, Pilot... so I was exposed to a lot of non-C-family stuff.

What does this mean? Exception in thread "main" java.lang.ClassCastException: clojure.lang.LazySeq cannot be cast to java.lang.String

I guess I did use MIPs for some classes, but very few and it was a long time ago

Well, it means you passed a lazy sequence to something that wanted a string or tried to convert it to string... stack trace and code?

You'll quickly learn to interpret that exception in the context of your code -- and this one java.lang.ClassCastException: <sometype> cannot be cast to clojure.lang.IFn which means you have something in the "call" position of an expression that is not a function, e.g., ("foo" 1 2 3)

Here is the exception:

Exception in thread "main" java.lang.ClassCastException: clojure.lang.LazySeq cannot be cast to java.lang.String
        at app.core.support(Unknown Source)
        at app.Application.main(Application.java:17)

All I did was add a where clause to that simple query I posted above\

Show me the code...

(since that stack trace is... less than helpful 🙂 )

(def simpleQuery "SELECT * FROM table WHERE col = 2")
  (j/query db2 [simpleQuery])

Is app.core.support your Clojure namespace?

Ya from what I've seen the stacktraces are not as helpful as java, unless I don't quite understand them

My namespace is app.core

How exactly are you calling your Clojure from Java?

The method being called is support

I've just been calling it in the static main function (which could possibly be an issue) to play around with core.support("FIRST");

I need to see more code than that...

public static void main(String[] args) {
        core.support("FIRST");
        SpringApplication.run(Application.class, args);
    }

I don't understand the context of that code -- what is core? how is suppport defined? what does your ns form look like.

(ns app.core
  (:require [clojure.java.jdbc :as j]
            [clojure.string :as str])
  (:gen-class
        :name app.core
        :methods [#^{:static true} [support [String] String]]))

(defn -support [x]
  (def simpleQuery "SELECT * FROM table WHERE col = 2")
  (j/query db2 [simpleQuery])
)

Ah, so you've declared -support to return a String, but you're returning a sequence -- the result of j/query is a sequence of hash maps.

How do I specify that?

Would it just be map?

Trying to learn Clojure by calling it from Java is going to be a pretty painful way to do things... you're trying to learn gen-class (which folks generally don't use) and combining Java types and Clojure types and so on...

j/query should return a fully realized sequence so that part itself won't be lazy but I suspect the default attempt to turn it into a String creates a lazy sequence somewhere.

Ok, is there a way thats different from gen-class?

Off the top of my head, I'm not sure what Java interfaces would be implemented by that sequence -- I'd have to try it in a REPL.

Or should I learn it separately?

Learn it separately would be my advice.

There's a huge amount of "incidental complexity" in the Java/Clojure interop that will get in the way of learning and debugging Clojure (e.g., that terrible stack trace)

Ah, yes, you do get a lazy sequence back from j/query but it is fully realized under the hood (as it consumed the ResultSet).

Maybe I'll split the project into 2, I've been trying to get it working this way because at my work we already have java services, I was hoping I could get them to work together in the same project

user> (query {:dbtype "mysql" :dbname "worldsingles" :user "myuser" :password "secret"} "select * from status")
=> 
({:name "approved", :id 1}
 {:name "new", :id 2}
 {:name "rejected", :id 3})
user> (type *1)
=>
clojure.lang.LazySeq
user> (ancestors *1)
=>
#{java.lang.Object
  clojure.lang.Obj
  clojure.lang.ISeq
  clojure.lang.IPending
  java.util.Collection
  clojure.lang.IPersistentCollection
  clojure.lang.IHashEq
  clojure.lang.IObj
  clojure.lang.IMeta
  clojure.lang.Sequential
  clojure.lang.Seqable
  java.io.Serializable
  java.util.List
  java.lang.Iterable}

(working from the REPL is so much easier!)

How do I add dependencies to the REPL?

like the clojure.java.jdbc for example

There are several possibilities: use the command line clj script with a deps.edn file; use Boot (a build tool); use Leiningen (another build tool). I recommend Boot -- http://boot-clj.com

Because then you can just do boot -d org.clojure/java.jdbc repl and get a REPL with the latest version of clojure.java.jdbc running.

Thats awesome

I

I'll try that

(you can use -d to specify anything that gradle would pull in for you)

Because you'll need to pull in the Ingres JDBC driver as well...

boot -d com.ingres.jdbc/iijdbc -d org.clojure/java.jdbc repl should do that.

@josmith2016 if you hit any Boot-specific questions, there's a #boot channel but I'm happy to answer them here in the context of getting you up and running with SQL stuff 🙂

Thank you 🙂

What IDE do you use to develop clojure @seancorfield?

Atom with ProtoREPL. I used to use Emacs (for years!).

@josmith2016 did you find the Ingres driver you needed? It looks like https://www.actian.com/data-management/ingres-sql-rdbms/ is the current product

http://esd.actian.com/product/drivers/JDBC/java/JDBC

Yes I did, thank you @danielcompton

As I query a database with the clojure.java.jdbc library, it is returning a clojure.lang.LazySeq. How do I change this to a list or map I can use in java?

@josmith2016 As I noted above, a LazySeq implements java.util.Collection and java.lang.Iterable so you can use it like either of those Java types.

I get this stacktrace when trying to cast it to a collection: Exception in thread "main" java.lang.ClassCastException: clojure.lang.LazySeq cannot be cast to clojure.lang.IFn

You're trying to use the result of the query as a function I expect. Again, show the code and the top of the stacktrace (down to where it comes into your code).

(That was one of the two exceptions I called out specifically above as being common for folks new to Clojure)

Here is the clojure method

(defn -support [x]
  (def simpleQuery "SELECT * FROM table")
  (j/query db [simpleQuery])
)

How do you have it declared in gen-class now?

(:gen-class
        :name app.core
        :methods [#^{:static true} [support [String] java.util.Collection]])

OK, and what does your Java look like now?

Collection list = core.support("FIRST");

And the top of the stacktrace?

BTW, do not use def inside defn -- def is for top-level definitions only.

What should I use instead?

If you want a local "variable", use let

(let [simple-query "SELECT * FROM table"]
  (j/query db [simple-query]))

(getting a coffee -- back in five)

I guess that worked, I got the error when trying to cast it to an array list in my java code. System.out.println((ArrayList<Object>) list);

I got it working by declaring a new ArrayList like this: System.out.println(new ArrayList<Object>(list));

Would the simple-query variable only exist until the end of that end parenthesis? or would it be available throughout the rest of the method?

(back)

Bindings introduced in let exist until its closing )

def always defines a Var and a top-level binding (even if it nested inside a function).

Ok that makes sense, I tried using let but couldn’t get it working because I thought it lasted the whole method like in java

Thanks so much for all your help, You saved me a ton of time. Multiple days worth of work probably

One more question

I’ve seen something where you can declare keywords

for example

If I’m declaring a database connection map like this

(def db-connect {:dbtype "ingres"
           :classname "com.ingres.jdbc.IngresDriver"
           :dbname ":dbname"
           :host "host"
           :port "I17"
           :user "user"
           :password "pass"})

you can use a function for it, as long as it emits a string

Can you show me an example?

e.g. for my prod code i do

{
    :port 4000
    :host "0.0.0.0"
    :uri ""
    :db  {:dbtype "postgresql"
          :dbname (slurp "/run/secrets/postgres-db")
          :host "postgres"
          :user (slurp "/run/secrets/postgres-user")
          :password (slurp "/run/secrets/postgres-passwd")}
}

(this is in a docker swarm)

The other thing you can do is use assoc to produce a new hash map with :dbname updated:

(def db {:dbtype ... :dbname ...})
(j/query (assoc db :dbname "newdb") ["select * from whatever"]))

@josmith2016 We do something similar to @jgh’s suggestion at work: we pull all of the settings that can change from an environment/configuration library (that uses EDN files on disk mostly), and we build all our db-specs at application startup since we use c3p0 for connection pooling.

Examples of reusing connections (directly in clojure.java.jdbc or via connection pooling) in the docs http://clojure-doc.org/articles/ecosystem/java_jdbc/reusing_connections.html