createDBConn.js

import datascript from 'datascript';
window.d = datascript;


export default () => {
/**
 * Define a schema for a graph of users (with the names declared to be
 * unique which allows better performance, along with being able to easily lookup
 * an entity by this unique identifier)
 *
 * The users are connected by the 'follows' attribute (which is defined as a
 * reference type, with a cardinality of 'many' since someone can follow more
 * than one person.)
 */
  const twitterUserSchema = {
    name: {
      ':db/cardinality': ':db.cardinality/one',
      ':db/unique': ':db.unique/identity'
    },
    follows: {
      ':db/cardinality': ':db.cardinality/many',
      ':db/valueType': ':db.type/ref'
    }
  };

  /**
   * Create connection to db (that's been instantiated with the schema above.)
   */
  const conn = datascript.create_conn(twitterUserSchema);

  /**
   * Define some seed data; including some `follower` references (that make
   * use of a temporary id to point to other entities within the array.)
   */
  const datoms = [
    {
      ':db/id': -1,
      name: 'John',
      follows: -3
    },
    {
      ':db/id': -2,
      name: 'David',
      follows: [-3, -1]
    },
    {
      ':db/id': -3,
      name: 'Jane'
    }
  ];

  /**
   * Transact in the data, to be stored and indexed by datascript for performant
   * querying.
   */
  datascript.transact(conn, datoms);
  return conn;
};