calcite-clj - Use Apache Calcite from Clojure
Small library to facilitate the implementation of calcite adapters in clojure.
It implements org.apache.calcite.schema.SchemaFactory and delegates to a Clojure function. See https://calcite.apache.org/javadocAggregate/org/apache/calcite/schema/SchemaFactory.html and https://calcite.apache.org/docs/tutorial.html for more information.
# Build with tools.build
clj -T:build ci
Small library used as a bridge from calcite to clojure: 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" } } ] }
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