Entity management on top of key-value stores
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README.org

Kampbell

Entity layer for key-value stores

Kampbell is designed to persist entities on top of key-value stores. By entities we mean the units of a domain model in an application: the user, the product, the order, etc. Think of an entity as a row in a table.

The aim is avoiding the cognitive overhead of database integration in the early stages of application development, and yet be able to persist data.

  • no foreign keys
  • no uuids
  • no query DSL
  • no drivers
  • no bindings
  • no dependencies

Just plain ol’ data and the joy of manipulating it with functions from the core library.

Kampbell has the potential to be a generic interface for multiple key-value store implementation, but currently consists of a single implementation on top of Konserve. Konserve is key-value database protocol that leverages the strengths of Clojure to offer a most compelling value proposition.

The public API of Kampbell is compatible with Clojure/Clojurescript. Some additional functionality is currently Clojure-only.

Concepts

In Kampbell, a collection (of entities) is structured as a vector of maps. In the underlying key-value store, keys are names for the collection of entities (eg. users, products, orders), and values are the entities themselves (serialized vector of maps).

  • All database transactions are validated by specs. You cannot persist bad data in the database. This is as good as your specs are.
  • Prior to inserting a new entry, Kampbell will check that it isn’t a duplicate.
  • Updating an entry is only possible if you provide all the specs complementing modified fields. This is by design: express your intent, and allow the software to validate it.

Installation

https://clojars.org/org.danielsz/kampbell/latest-version.svg

Usage

The public API consists of the four operations: get-entity, save-entity, update-entity and delete-entity. Additionally, to get the entire collection, use get-entities.

The test included in the current repository contains a basic implementation that demonstrate the capabilities of Kampbell.

Here are our specs.

(s/def :domain.user/name string?)
(s/def :domain.user/email (s/and string? #(re-matches #"^[a-zA-Z0-9._%+-]+@[a-zA-Z0-9.-]+\.[a-zA-Z]{2,63}" %)))
(s/def :domain/user (s/keys :req [:domain.user/name
                                  :domain.user/email]))

Here is a reference implementation.

(defn save-user [db v]
  (let [v (assoc v :domain.utils/created-at (Instant/now))]
    (<!! (k/save-entity db :domain/user v))))

(defn get-users [db]
  (<!! (k/get-entities db "users")))

(defn get-user [db v]
  (<!! (k/get-entity db "users" :domain.user/email v)))

(defn update-user [db v & specs]
  {:pre [(some? specs) (every? keyword? specs)]}
  (<!! (k/update-entity db "users" v (into #{} specs))))

(defn delete-user [db v]
  (<!! (k/delete-entity db :domain/user v)))

Benchmarks

The design goal of Kampbell is rapid prototyping, not performance. Optimizations are possible, but are not a priority at this point. Due to the file-based nature of the persistence used, Kampbell will run circles around systems that persist data over the wire. Up to a certain a volume, that is. If you’re interested in contributing your own benchmarks, we’ll be happy to publish or link to yours.

Advanced

When you define the persistence layer in an application as an interface, you gain the freedom of swapping the particular implementation at any time.

(defprotocol MyApplication
  "Persistence protocol for the application"
  (get-users [db])
  (get-user [db v])
  (save-user [db v])
  (update-user [db v specs])
  (delete-user [db v])