It is an OSS library that is API compatible with the product called Datomic, which is famous in the Clojure world. I was interested in Datascript, so I touched it.
Let's trace Datomic's Getting Started as a subject.
Add [datascript" 0.16.1 "] to : dependencies
(require '[datascript.core :as dc])
(def con (dc/create-conn))
In this example, we model a movie. It is assumed that the movie has a release year, a genre, and a title attribute.
The following is required to define the attribute.
--Unique name of : db / ident attribute
--: db / valueType The type of data held by the attribute
--Whether the data in the : db / cardinality attribute has a single value or holds a collection
It is also recommended to define the attribute docstring in any: db / doc.
attributes are defined in the map of the data.
The title is defined as follows
{:db/ident :movie/title
:db/valueType :db.type/string
:db/cardinality :db.cardinality/one
:db/doc "The title of the movie"}
The genre is as follows
{:db/ident :movie/genre
:db/valueType :db.type/string
:db/cardinality :db.cardinality/one
:db/doc "The genre of the movie"}
Since the release year is an integer, change : db / valueType to: db.type / long and define it as follows
{:db/ident :movie/release-year
:db/valueType :db.type/long
:db/cardinality :db.cardinality/one
:db/doc "The year the movie was released in theaters"}
Schemas can be transacted one by one, but here we will transact them all together.
(dc/transact con [{:db/ident :movie/title
:db/valueType :db.type/string
:db/cardinality :db.cardinality/one
:db/doc "The title of the movie"}
{:db/ident :movie/genre
:db/valueType :db.type/string
:db/cardinality :db.cardinality/one
:db/doc "The genre of the movie"}
{:db/ident :movie/release-year
:db/valueType :db.type/long
:db/cardinality :db.cardinality/one
:db/doc "The year the movie was released in theaters"}])
If you evaluate con, you can see that something is in it.
user> con
#<Atom@4afb7219:
{1 :db/cardinality,
1 :db/doc,
1 :db/ident,
1 :db/valueType,
2 :db/cardinality,
2 :db/doc,
2 :db/ident,
2 :db/valueType,
3 :db/cardinality,
3 :db/doc,
3 :db/ident,
3 :db/valueType}
Define the following data
(def first-movies [{:movie/title "The Goonies"
:movie/genre "action/adventure"
:movie/release-year 1985}
{:movie/title "Commando"
:movie/genre "action/adventure"
:movie/release-year 1985}
{:movie/title "Repo Man"
:movie/genre "punk dystopia"
:movie/release-year 1984}])
Transact and add to DB like schema
(dc/transact con first-movies)
If you evaluate con again, you can see that something is increasing.
user> con
#<Atom@4afb7219:
{1 :db/cardinality,
1 :db/doc,
1 :db/ident,
1 :db/valueType,
2 :db/cardinality,
2 :db/doc,
2 :db/ident,
2 :db/valueType,
3 :db/cardinality,
3 :db/doc,
3 :db/ident,
3 :db/valueType,
4 :movie/genre,
4 :movie/release-year,
4 :movie/title,
5 :movie/genre,
5 :movie/release-year,
5 :movie/title,
6 :movie/genre,
6 :movie/release-year,
6 :movie/title}
First, create something called db from the connection.
(def db (dc/db con))
This db is immutable and is guaranteed to return the same results for the same query (likely a point of interest).
There are two ways to get the value from the DB:
--Throw a query in the declarative query language query Datalog
--pull Declaratively hierarchize and select information about entertainment
Try to find the one with the attribute of : movie / title in the db
(dc/q '[:find ?e
:where [?e :movie/title]]
db)
=>#{[4] [6] [5]}
To extract movie titles instead of entertainment IDs:
(dc/q '[:find ?movie-title
:where [_ :movie/title ?movie-title]]
db)
=> #{["The Goonies"] ["Commando"] ["Repo Man"]}
Get the title of a movie with a release year of 1985 as follows
(dc/q '[:find ?title
:where [?e :movie/title ?title]
[?e :movie/release-year 1985]]
db)
=>#{["The Goonies"] ["Commando"]}
Information on all attributes of movies released in 1985 can be obtained as follows:
(dc/q '[:find ?title ?year ?genre
:where [?e :movie/title ?title]
[?e :movie/release-year ?year]
[?e :movie/genre ?genre]
[?e :movie/release-year 1985]]
db)
=> #{["The Goonies" 1985 "action/adventure"]
["Commando" 1985 "action/adventure"]}
Use pull as follows
(dc/pull db
'[*] ;;selector
4 ;; entity id
)
=>{:db/id 4,
:movie/genre "action/adventure",
:movie/release-year 1985,
:movie/title "The Goonies"}
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