Datomic queries against Java collections

gistfile1.java

// Datomic example code

package datomic.examples;

import java.util.Collection;
import java.util.Iterator;
import java.util.List;
import java.util.Set;

import static datomic.Peer.*;
import static datomic.Util.*;

public class BindingExamples {
    public static void printRelation(Collection stuff) {
        for (Iterator iterator = stuff.iterator(); iterator.hasNext();) {
            List tuple =  (List) iterator.next();
            for (Iterator itt = tuple.iterator(); itt.hasNext();) {
                Object next = itt.next();
                System.out.print(next);
                System.out.print(" ");
            }
            System.out.println("");
        }    
    }
    public static void main(String[] args) {
        System.out.println("\nScalar binding...");
        // ?answer binds a scalar
        printRelation(q("[:find ?answer :in ?answer]", 42));

        System.out.println("\nBinding 2 variables...");
        // bind as many variables as you want
        printRelation(q("[:find ?last ?first :in ?last ?first]",
                        "Doe",
                        "John"));

        System.out.println("\nTuple Binding...");
        // [?last ?first?] binds a tuple
        printRelation(q("[:find ?last ?first :in [?last ?first]]",
                         list("Doe", "John")));

        System.out.println("\nCollection Binding...");
        // [?first ...] binds a collection
        printRelation(q("[:find ?first :in [?first ...]]",
                        list("John", "Jane", "Phineas")));


        System.out.println("\nRelation Binding...");
        // [[?first ?last]] binds a relation
        printRelation(q("[:find ?first :in [[?first ?last]]]",
                        list(list("John", "Doe"),
                             list("Jane", "Doe"))));

        Object firstName = read(":firstName");
        Object lastName = read(":lastName");
        Object email = read(":email");
        Object height = read(":height");

        System.out.println("\nDatabase binding...");
        // a database binding name starts with $ instead of ?
        // any relation with 4-tuples E/A/V/T can act as a database
        // so in Datomic, you can mock a database with a list of lists
        printRelation(q("[:find ?first" +
                "         :in $db " +
                "         :where [$db _ :firstName ?first]]",
                list(list(1, firstName, "John", 42))));

        // Similar to previous. You can omit the $db and the :in when
        // querying against a single database.
        System.out.println("\nDefault database binding...");
        printRelation(q("[:find ?first" +
                "         :where [_ :firstName ?first]]",
                list(list(1, firstName, "John", 42),
                     list(1, lastName, "Doe", 42))));

        // cross-database in-memory join, two database bindings
        System.out.println("\nIn-memory, cross database join, two database bindings...");
        printRelation(q("[:find ?first ?height" +
                "         :in $db1 $db2" +
                "         :where [$db1 ?e1 :firstName ?first]" +
                "                [$db1 ?e1 :email ?email]" +
                "                [$db2 ?e2 :email ?email]" +
                "                [$db2 ?e2 :height ?height]]" ,
                // database 1
                list(list(1, firstName,  "John"),
                     list(1, email, "jdoe@example.com"),
                     list(2, firstName, "Jane"),
                     list(2, email, "jane@example.com")),
                // database 2
                list(list(100, email, "jane@example.com"),
                     list(100, height, 73),
                     list(101, email, "jdoe@example.com"),
                     list(101, height, 71)
                )));

        // use query for every collection manipulation tasks
        // compare to http://stackoverflow.com/questions/3717939/iterating-and-processing-an-arraylist
        System.out.println("\nQuery with filtering predicate...");
        printRelation(q("[:find ?car ?speed" +
                "         :in [[?car ?speed]]" +
                "         :where [(> ?speed 100)]]",
                list(list("Stock", 225),
                     list("Spud", 80),
                     list("Rocket", 400),
                     list("Stock", 225),
                     list("Clunker", 40))));


    }
}