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(ns datascript-demo
"A quick Tour of DataScript features."
(:require [datascript.core :as dt]))
;;;; Declaring the (minimal required) schema of our DB
(def db-schema
{:person/name {:db/unique :db.unique/identity} ;; Persons are uniquely identified by thier :person/name
:movie/title {:db/unique :db.unique/identity} ;; Movies are uniquely identified by thier :movie/title
:movie/director {:db/valueType :db.type/ref ;; a Movie has one director
:db/cardinality :db.cardinality/one}
:movie/actors {:db/valueType :db.type/ref ;; a Movie has several Actors
:db/cardinality :db.cardinality/many}})
;; NOTE:
;; 1. In the schema, we only need to declare the attributes that have special behaviour;
;; for instance, we didn't need to declare :movie/release-year or :person/gender.
;; 2. We only need to declare attributes, there's no notion of table / collection / entity-type.
;;;; Creating an empty db
(def empty-db (dt/db (dt/create-conn db-schema)))
;;;; Writing data
(def db
(dt/db-with empty-db
;; This data structure below is a DataScript 'write', or 'transaction request'.
;; It is composed of maps, each map grouping several facts about an entity.
;; Notice how several facts about an entity can be spread over several maps and
;; will be automatically reconciled: for example, facts about the movie "The Good, the Bad and The Ugly"
;; are specified in 3 different maps.
[{:movie/title "Star Wars: a New Hope"
:movie/release-year 1977
:movie/director {:person/name "George Lucas"}
:movie/actors [{:person/name "Carrie Fisher"}
{:person/name "Harrison Ford"
:person/gender :gender/male}]}
{:person/name "George Lucas"
:person/gender :gender/male}
{:person/name "Carrie Fisher"
:person/gender :gender/female}
{:movie/title "The Good, the Bad and The Ugly"
:movie/release-year 1966}
{:movie/title "The Good, the Bad and The Ugly"
:movie/director {:person/name "Sergio Leone"}}
{:movie/title "Gran Torino"
:movie/release-year 2008}
{:person/name "Clint Eastwood"
:movie/_director [{:movie/title "Gran Torino"}]
:movie/_actors [{:movie/title "The Good, the Bad and The Ugly"}]}
]))
;;;; Querying
(comment
;; Let's see the whole contents of the db
db
=> #datascript/DB{:schema {:person/name {:db/unique :db.unique/identity},
:movie/title {:db/unique :db.unique/identity},
:movie/director {:db/valueType :db.type/ref, :db/cardinality :db.cardinality/one},
:movie/actors {:db/valueType :db.type/ref, :db/cardinality :db.cardinality/many}},
:datoms [[1 :movie/actors 3 536870913]
[1 :movie/actors 4 536870913]
[1 :movie/director 2 536870913]
[1 :movie/release-year 1977 536870913]
[1 :movie/title "Star Wars: a New Hope" 536870913]
[2 :person/gender :gender/male 536870913]
[2 :person/name "George Lucas" 536870913]
[3 :person/gender :gender/female 536870913]
[3 :person/name "Carrie Fisher" 536870913]
[4 :person/gender :gender/male 536870913]
[4 :person/name "Harrison Ford" 536870913]
[5 :movie/actors 8 536870913]
[5 :movie/director 6 536870913]
[5 :movie/release-year 1966 536870913]
[5 :movie/title "The Good, the Bad and The Ugly" 536870913]
[6 :person/name "Sergio Leone" 536870913]
[7 :movie/director 8 536870913]
[7 :movie/release-year 2008 536870913]
[7 :movie/title "Gran Torino" 536870913]
[8 :person/name "Clint Eastwood" 536870913]]}
;; Find the names of all persons in db
(dt/q ;; Datalog API
'[:find [?name ...] :where
[?p :person/name ?name]]
db)
=> ["Harrison Ford" "Clint Eastwood" "Carrie Fisher" "Sergio Leone" "George Lucas"]
;; Find the names of all actors in DB
(dt/q
'[:find [?name ...] :where
[?m :movie/actors ?p]
[?p :person/name ?name]]
db)
=> ["Harrison Ford" "Clint Eastwood" "Carrie Fisher"]
;; What do we know about the Star Wars movie?
(def star-wars
(dt/entity db [:movie/title "Star Wars: a New Hope"])) ;; Entity API
star-wars ;; a DataScript Entity is a lazy, Map-like view of the database, centered around a given entity.
=> {:db/id 2}
(:movie/title star-wars)
=> "Star Wars: a New Hope"
(:movie/release-year star-wars)
=> 1977
(type star-wars)
=> datascript.impl.entity.Entity ;; although an Entity looks like a Map, it is not an ordinary Map.
(dt/touch star-wars) ;; `dt/touch`: load all attributes in the Entity's cache.
=>
{:movie/actors #{{:db/id 4} {:db/id 3}}, ;; in an Entity, the values are either scalars (strings, numbers, etc.)
:movie/director {:db/id 1}, ;; or other Entities.
:movie/release-year 1977,
:movie/title "Star Wars: a New Hope",
:db/id 2}
;; who's the director ?
(-> star-wars :movie/director dt/touch) ;; following a reference-typed attribute navigates to another Entity
=> {:person/gender :gender/male,
:person/name "George Lucas",
:db/id 1}
;; Find all movies released after 1970
(->>
(dt/q '[:find [?m ...] :in $ ?time :where
[?m :movie/release-year ?t]
[(> ?t ?time)]]
db 1970)
(map #(dt/entity db %))
(sort-by :movie/release-year)
(mapv dt/touch))
=>
[{:movie/actors #{{:db/id 4} {:db/id 3}},
:movie/director {:db/id 1},
:movie/release-year 1977,
:movie/title "Star Wars: a New Hope",
:db/id 2}
{:movie/director {:db/id 8},
:movie/release-year 2008,
:movie/title "Gran Torino",
:db/id 7}]
)