Commit f36ddbf

<version>0.9.5127</version>

package datomic.samples;

import datomic.Connection;

import datomic.Database;

import java.util.*;

import static datomic.Peer.*;

import static datomic.Util.read;

import static datomic.samples.Fns.scratchConnection;

import static datomic.samples.Schema.CARDINALITY_MANY;

import static datomic.samples.Schema.CARDINALITY_ONE;

import static datomic.samples.Schema.cardinality;

public class MaybeQuery {

/**

public static Object maybe(Object db, Object e, Object attr, Object ifNot) {

Collection<List<Object>> result = query("[:find ?v " +

":in $ ?e ?a " +

":where [?e ?a ?v]]", db, e, attr);

if (result.isEmpty()) {

return ifNot;

} else {

Object card = cardinality(db, attr);

if (card.equals(CARDINALITY_ONE)) return result.iterator().next(); // only one in list

Set acc = new HashSet();

for (Iterator<List<Object>> iterator = result.iterator(); iterator.hasNext(); ) {

acc.add(iterator.next());

}

return Collections.unmodifiableSet(acc);

}

}

public static String rules =

"[[[attr-in-namespace ?e ?ns2]\n" +

" [?e :db/ident ?a]\n" +

" [?e :db/valueType]\n" +

" [(namespace ?a) ?ns1]\n" +

" [(= ?ns1 ?ns2)]]]";

public static void main(String[] args) {

Connection conn = scratchConnection();

Database db = conn.db();

System.out.println("Maybe entity zero has a docstring...");

System.out.println(maybe(db, 0, read(":db/doc"), "<docstring missing>"));

System.out.println("\nMaybe entity zero has installed some atttributes");

System.out.println(maybe(db, 0, read(":db.install/attribute"), "<no attributes installed>"));

System.out.println("\nMaybe entity one has installed some attributes");

System.out.println(maybe(db, 1, read(":db.install/attribute"), "<no attributes installed>"));

System.out.println("\nMaybe we can call maybe from inside a query");

System.out.println(q("[:find ?ident ?card" +

" :where [?e :db/ident ?ident]" +

" [(datomic.samples.MaybeQuery/maybe $ ?e :db/cardinality \"<none>\") ?card]]",

db));

System.out.println("Look up attributes in the db namespace:");

System.out.println(q(

"[:find ?e ?ident\n" +

" :in $ %\n" +

" :where\n" +

" (attr-in-namespace ?e \"db\")\n" +

" [?e :db/ident ?ident]]",

db, rules));

}

}

import datomic.Peer;

import datomic.Util;

import java.util.Scanner;

import java.util.Collection;

public static void main(String[] args) {

// Your connection information for local mbrainz 1968-1973 subset goes here.

String uri = "datomic:free://localhost:4334/mbrainz-1968-1973";

// Connect to transactor, get latest database value from storage.

Connection conn = Peer.connect(uri);

System.out.println("All releases in the database with release names.");

Collection results = Peer.query("[:find ?release-name :where [_ :release/name ?release-name]]", db);

System.out.println(results);

pause();

System.out.println("Same as previous query, but with explicit db-var ($).");

results = Peer.query("[:find ?release-name :in $ :where [$ _ :release/name ?release-name]]", db);

System.out.println(results);

pause();

System.out.println("Query that finds releases by artist. Parameterized to accept artist name as an argument.");

results = Peer.query("[:find ?release-name " +

":in $ ?artist-name " +

":where [?artist :artist/name ?artist-name] " +

"[?release :release/artists ?artist] " +

"[?release :release/name ?release-name]]",

db, "John Lennon");

System.out.println(results);

pause();

System.out.println("This query accepts a relation argument as a vector and destructures it within the :in.");

results = Peer.query("[:find ?release " +

" :in $ [?artist-name ?release-name] " +

" :where [?artist :artist/name ?artist-name] " +

" [?release :release/artists ?artist] " +

" [?release :release/name ?release-name]]",

db, Util.list("John Lennon", "Mind Games"));

System.out.println(results);

pause();

System.out.println("This query accepts a list of artist arguments and uses destructuring to satisfy the " +

"query for each of them (union of results).");

results = Peer.query("[:find ?release-name " +

":in $ [?artist-name ...] " +

":where [?artist :artist/name ?artist-name] " +

" [?release :release/artists ?artist] " +

" [?release :release/name ?release-name]]",

db, Util.list("Paul McCartney", "George Harrison"));

pause();

System.out.println("This query accepts a list of relations, also a list, and destructures the arguments in " +

"the :in clause.");

results = Peer.query("[:find ?release " +

":in $ [[?artist-name ?release-name]] " +

":where [?artist :artist/name ?artist-name] " +

" [?release :release/artists ?artist] " +

" [?release :release/name ?release-name]]",

db, Util.list(Util.list("John Lennon", "Mind Games"),

Util.list("Paul McCartney", "Ram")));

System.out.println(results);

pause();

System.out.println("This query returns a collection of relations, all artists and their releases.");

results = Peer.query("[:find ?artist-name ?release-name " +

":where [?release :release/name ?release-name] " +

" [?release :release/artists ?artist] " +

" [?artist :artist/name ?artist-name]]",

db);

System.out.println(results);

pause();

System.out.println("This query returns a list of releases by using a find specification.");

results = Peer.query("[:find [?release-name ...]" +

" :in $ ?artist-name " +

" :where [?artist :artist/name ?artist-name] " +

" [?release :release/artists ?artist] " +

" [?release :release/name ?release-name]]",

db, "John Lennon");

System.out.println(results);

pause();

System.out.println("This query returns values from multiple attributes to provide artist's start date.");

results = Peer.query("[:find [?year ?month ?day] " +

" :in $ ?name " +

" :where [?artist :artist/name ?name] " +

" [?artist :artist/startDay ?day] " +

" [?artist :artist/startMonth ?month] " +

" [?artist :artist/startYear ?year]]",

db, "John Lennon");

System.out.println(results);

pause();

System.out.println("Return just the year of start date using a scalar find specification.");

Long year = Peer.query("[:find ?year . " +

" :in $ ?name " +

" :where [?artist :artist/name ?name] " +

" [?artist :artist/startYear ?year]]",

db, "John Lennon");

System.out.println(year);

pause();

System.out.println("Total number of artists without :artist/country attribute.");

Integer res = Peer.query("[:find (count ?eid) . " +

":where [?eid :artist/name] " +

"(not [?eid :artist/country])]",

db);

System.out.println(res);

pause();

System.out.println("Number of artists missing either country or gender. "+

"(negation of conjunction reads 'not (clause1 and clause2)'");

res = Peer.query("[:find (count ?eid) . " +

":where [?eid :artist/name] " +

"(not [?eid :artist/country] " +

"[?eid :artist/gender])]",

db);

System.out.println(res);

pause();

System.out.println("Use not-join to bind variable in subquery. Artists w/o releases in 1970.");

res = Peer.query("[:find (count ?artist) . " +

":where [?artist :artist/name] " +

"(not-join [?artist] " +

" [?release :release/artists ?artist] " +

" [?release :release/year 1970])]",

db);

System.out.println(res);

pause();

System.out.println("Total of artists who are a group or female by use of 'or'.");

res = Peer.query("[:find (count ?artist) . " +

" :where (or [?artist :artist/type :artist.type/group] " +

" (and [?artist :artist/type :artist.type/person] " +

" [?artist :artist/gender :artist.gender/female]))]",

db);

System.out.println(res);

pause();

System.out.println("Count of releases from Canadian artists or the year 1970 using 'or-join'");

res = Peer.query("[:find (count ?release) . " +

" :where [?release :release/name] " +

" (or-join [?release] " +

" (and [?release :release/artists ?artist] " +

" [?artist :artist/country :country/CA]) " +

" [?release :release/year 1970])]",

db);

System.out.println(res);

pause();

}

private static final Scanner scanner = new Scanner(System.in);

private static void pause() {

if (System.getProperty("NOPAUSE") == null) {

System.out.println("\nPress enter to continue...");

scanner.nextLine();

}