datascript: A Clojure repository from M-xparker

What if creating a database would be as cheap as creating a Hashmap?

An immutable in-memory database and Datalog query engine in Clojure and ClojureScript.

DataScript is meant to run inside the browser. It is cheap to create, quick to query and ephemeral. You create a database on page load, put some data in it, track changes, do queries and forget about it when the user closes the page.

DataScript databases are immutable and based on persistent data structures. In fact, they’re more like data structures than databases (think Hashmap). Unlike querying a real SQL DB, when you query DataScript, it all comes down to a Hashmap lookup. Or series of lookups. Or array iteration. There’s no particular overhead to it. You put a little data in it, it’s fast. You put in a lot of data, well, at least it has indexes. That should do better than you filtering an array by hand anyway. The thing is really lightweight.

The intention with DataScript is to be a basic building block in client-side applications that needs to track a lot of state during their lifetime. There’s a lot of benefits:

Central, uniform approach to manage all application state. Clients working with state become decoupled and independent: rendering, server sync, undo/redo do not interfere with each other.
Immutability simplifies things even in a single-threaded browser environment. Keep track of app state evolution, rewind to any point in time, always render consistent state, sync in background without locking anybody.
Datalog query engine to answer non-trivial questions about current app state.
Structured format to track data coming in and out of DB. Datalog queries can be run against it too.

Latest version

[datascript "0.16.9"]

Support us

Resources

Support:

Join #datascript on Clojurians Slack (grab invite here)

Books:

Learning ClojureScript has a chapter on DataScript

Docs:

Posts:

Talks:

“Frontend with Joy” talk (FPConf, August 2015): video in Russian
“Programming Web UI with Database in a Browser” talk (PolyConf, July 2015): slides, video
“DataScript for Web Development” talk (Clojure eXchange, Dec 2014): slides, video
“Building ToDo list with DataScript” webinar (ClojureScript NYC, Dec 2014): video, app
DataScript hangout (May 2014, in Russian): video

Projects using DataScript:

Precursor, collaborative prototyping tool
LightMesh, datacenter management
Cognician, coaching platform
bitfountain, iOS courses
PartsBox, electronic parts management
I am Fy, accessories e-shop
Acha-acha, github achievements (sources, code walkthrough)
Showkr, flickr gallery viewer (sources)
Zetawar, turn-based tactical strategy game
Lemmings, incubator focused on art & artificial intelligence

Related projects:

DataScript-Transit, transit serialization for database and datoms
Posh, lib that lets you use a single DataScript db to store Reagent app state
re-posh, use re-frame with DataScript storage
DataScript-mori, DataScript & Mori wrapper for use from JS
DatSync, Datomic ↔︎ DataScript syncing/replication utilities
Intension, lib to convert associative structures to in-memory databases for querying them
Datamaps, lib designed to leverage datalog queries to query arbitrary maps.

Demo applications:

Localisation Demo with Om Next
ToDo, task manager demo app (persistence via localStorage and transit, filtering, undo/redo): sources, live
CatChat, chat demo app: sources, code walkthrough, live
clj-crud, demo CRUD app: sources, blog post
OmNext TodoMVC

Usage examples

For more examples, see our acceptance test suite.

(require '[datascript.core :as d])

;; Implicit join, multi-valued attribute

(let [schema {:aka {:db/cardinality :db.cardinality/many}}
      conn   (d/create-conn schema)]
  (d/transact! conn [ { :db/id -1
                        :name  "Maksim"
                        :age   45
                        :aka   ["Max Otto von Stierlitz", "Jack Ryan"] } ])
  (d/q '[ :find  ?n ?a
          :where [?e :aka "Max Otto von Stierlitz"]
                 [?e :name ?n]
                 [?e :age  ?a] ]
       @conn))

;; => #{ ["Maksim" 45] }


;; Destructuring, function call, predicate call, query over collection

(d/q '[ :find  ?k ?x
        :in    [[?k [?min ?max]] ...] ?range
        :where [(?range ?min ?max) [?x ...]]
               [(even? ?x)] ]
      { :a [1 7], :b [2 4] }
      range)

;; => #{ [:a 2] [:a 4] [:a 6] [:b 2] }


;; Recursive rule

(d/q '[ :find  ?u1 ?u2
        :in    $ %
        :where (follows ?u1 ?u2) ]
      [ [1 :follows 2]
        [2 :follows 3]
        [3 :follows 4] ]
     '[ [(follows ?e1 ?e2)
         [?e1 :follows ?e2]]
        [(follows ?e1 ?e2)
         [?e1 :follows ?t]
         (follows ?t ?e2)] ])

;; => #{ [1 2] [1 3] [1 4]
;;       [2 3] [2 4]
;;       [3 4] }


;; Aggregates

(d/q '[ :find ?color (max ?amount ?x) (min ?amount ?x)
        :in   [[?color ?x]] ?amount ]
     [[:red 10]  [:red 20] [:red 30] [:red 40] [:red 50]
      [:blue 7] [:blue 8]]
     3)

;; => [[:red  [30 40 50] [10 20 30]]
;;     [:blue [7 8] [7 8]]]

Using from vanilla JS

DataScript can be used from any JS engine without additional dependencies:

<script src="https://github.com/tonsky/datascript/releases/download/0.16.9/datascript-0.16.9.min.js"></script>

or as a CommonJS module (npm page):

npm install datascript

var ds = require('datascript');

or as a RequireJS module:

require(['datascript'], function(ds) { ... });

Queries:

Query and rules should be EDN passed as strings
Results of q are returned as regular JS arrays

Entities:

Entities returned by entity call are lazy as in Clojure
Use e.get("prop"), e.get(":db/id"), e.db to access entity properties
Entities implement ECMAScript 6 Map interface (has/get/keys/...)

Transactions:

Use strings such as ":db/id", ":db/add", etc. instead of db-namespaced keywords
Use regular JS arrays and objects to pass data to transact and db_with

Transaction reports:

report.tempids has string keys ("-1" for entity tempid -1), use resolve_tempid to set up a correspondence

Check out test/js/tests.js for usage examples.

Project status

Stable. Most of the features done, expecting non-breaking API additions and performance optimizations. No docs at the moment, use examples & Datomic documentation.

The following features are supported:

Database as a value: each DB is an immutable value. New DBs are created on top of old ones, but old ones stay perfectly valid too
Triple store model
EAVT, AEVT and AVET indexes
Multi-valued attributes via :db/cardinality :db.cardinality/many
Lazy entities and :db/valueType :db.type/ref auto-expansion
Database “mutations” via transact!
Callback-based analogue to txReportQueue via listen!
Direct index lookup and iteration via datoms and seek-datoms
Filtered databases via filter
Lookup refs
Unique constraints, upsert
Pull API (thx David Thomas Hume)

Query engine features:

Implicit joins
Query over DB or regular collections
Parameterized queries via :in clause
Tuple, collection, relation binding forms in :in clause
Query over multiple DB/collections
Predicates and user functions in query
Rules, recursive rules
Aggregates
Find specifications

Interface differences:

Conn is just an atom storing last DB value, use @conn instead of (d/db conn)
Instead of #db/id[:db.part/user -100] just use -100 in place of :db/id or entity id
Transactor functions can be called as [:db.fn/call f args] where f is a function reference and will take db as first argument (thx @thegeez)
In ClojureScript, custom query functions and aggregates should be passed as source instead of being referenced by symbol (due to lack of resolve in CLJS)
Custom aggregate functions are called via aggregate keyword: :find (aggregate ?myfn ?e) :in $ ?myfn
Additional :db.fn/retractAttribute shortcut
Transactions are not annotated by default with :db/txInstant

Expected soon:

Better error reporting
Proper documentation
Query clasues: not / not-join / or / or-join

Differences from Datomic

DataScript is built totally from scratch and is not related by any means to the popular Clojure database Datomic
Runs in a browser and/or in a JVM
Simplified schema, not queryable
Attributes do not have to be declared in advance. Put them to schema only when you need special behaviour from them
Any type can be used for values
No :db/ident attributes, keywords are literally attribute values, no integer id behind them
No schema migrations
No cache segments management, no laziness. Entire DB must reside in memory
No facilities to persist, transfer over the wire or sync DB with the server
No pluggable storage options, no full-text search, no partitions
No external dependencies
Free

Aimed at interactive, long-living browser applications, DataScript DBs operate in constant space. If you do not add new entities, just update existing ones, or clean up database from time to time, memory consumption will be limited. This is unlike Datomic which keeps history of all changes, thus grows monotonically. DataScript does not track history by default, but you can do it via your own code if needed.

Some of the features are omitted intentionally. Different apps have different needs in storing/transfering/keeping track of DB state. DataScript is a foundation to build exactly the right storage solution for your needs without selling too much “vision”.

License

Licensed under Eclipse Public License (see LICENSE).

M-xparker/datascript