Hello,
I would like to announce that I have ported the Calcite CSV example
(scannable table only) from Java to Clojure.
I did it mainly as an exercise: to learn how Calicte works and how it
would look with Clojure.
I learn a lot in the process and also discovered a Calcite bug
https://issues.apache.org/jira/browse/CALCITE-4966 .
If anyone is interested, my code is available here:
https://github.com/ieugen/clojure-training/tree/main/csv-clojure .
Id does need a version of Calcite with the fix for
https://issues.apache.org/jira/browse/CALCITE-4966 (I built and
deployed a local version).
It also needs a small 1 class library used as a bridge (build and
install locally):
https://github.com/ieugen/clojure-training/blob/main/csv-clojure/calcite-clj/src/main/java/ro.ieugen.calcite.clj/SchemaFactory.java
.
With the above code I was able to call code like this:
(let [db {:jdbcUrl "jdbc:calcite:model=resources/model.json"
:user "admin"
:password "admin"}
ds (jdbc/get-datasource db)]
(jdbc/execute! ds ["select * from emps where age is null or age >=
40"])))
and get back SQL results.
Part of the magic is in model.json file.
It uses ro.ieugen.calcite.clj.SchemaFactory and it has an operand property
"clojure-clj.schema-factory": "ro.ieugen.calcite-csv/csv-schema" .
This property is a reference to the Clojure namespace
(ro.ieugen.calcite-csv) and function (csv-schema) to call for generating
the Schema.
The schema factory is generic and if there is interest I would like to
contribute it upstream.
It allows the use of Clojure functions to be used as Schema factories
thus creating a bridge to Clojure in a seamless way.
Full model.json bellow:
```
{
"version": "1.0",
"defaultSchema": "SALES",
"schemas": [
{
"name": "SALES",
"type": "custom",
"factory": "ro.ieugen.calcite.clj.SchemaFactory",
"operand": {
"clojure-clj.schema-factory": "ro.ieugen.calcite-csv/csv-schema",
"directory": "resources/sales"
}
}
]
}
```
--
Eugen Stan
+40770 941 271 / https://www.netdava.combegin:vcard
fn:Eugen Stan
n:Stan;Eugen
email;internet:eugen.s...@netdava.com
tel;cell:+40720898747
x-mozilla-html:FALSE
url:https://www.netdava.com
version:2.1
end:vcard
