backend-development.md

Backend Development

Implementing a new backend to use for datahike does not require much effort as there are only a handful of methods for multimethods must be created. In order to keep things tidy, we have agreed on some conventions:

1. Keep all implementations for a backend within one namespace.
2. Name this namespace datahike-{backendname}.core.
3. Make sure, all multimethods are defined for the new backend you are developing.

As an example, you may have a look at the implementation of our JDBC backend, i.e. datahike-jdbc.

Template

We provide a basic template for a backend implementation here.

Following are bracketed text pieces defining placeholder values, you should replace as follows:

• backendname surprisingly should be the name of your backend.
• backendID should be a keyword to identify your backend on request. At this moment, datahike ships with backends identified by :mem and :file, so do not use those.
• indexID should be a keyword identifying an index to be used as default for your backend. So far, you can only use :datahike.index/hitchhiker-tree for your backend. In the future, we will support :datahike.index/persistent-set as well though.
• configSpec optional clojure.spec definition for configuration validation

You may add any configuration attributes to the store configuration. Only :backend is mandatory which refers to backendID.

In your core.clj:

(ns datahike-{backendname}.core
  (:require [datahike.store :as s]
            ;; your imports        
  ))


(defmethod s/empty-store {backendID} [config]
  ;; your implementation
  )

(defmethod s/delete-store {backendID} [config]
  ;; your implementation
  )

(defmethod connect-store {backendID} [config]
  ;; your implementation
  )

(defmethod release-store {backendID} [config store]
  ;; your implementation
  )

(defmethod scheme->index {backendID} [_]
  {indexID}
  )
  
(defmethod default-config {backendID} [config]
  ;; your implementation for default values e.g. from env vars or values from best practices
 )
 
(defmethod config-spec {backendID} [_] {configSpec})