code: private StatementResult makeFriends( final Transaction tx, final String person1, final String person2 )
      {
          return tx.run( "MATCH (a:Person {name: $person_1}) " +
                          "MATCH (b:Person {name: $person_2}) " +
                          "MERGE (a)-[:KNOWS]->(b)",
                  parameters( "person_1", person1, "person_2", person2 ) );
      }
docs: Create a friendship between two people.