knex migration sample - creating tables

knexmigration.js

exports.up = function(knex) {
  return (knex.schema
        .createTable('zoos', tbl => {
            tbl.increments();
            tbl.string('zoo_name', 128)
                .notNullable()
                .unique();
            tbl.string('address', 128)
                .notNullable()
                .unique();
        })
        .createTable('species', tbl=> {
            tbl.increments();
            tbl.string('species_name', 128)
                .notNullable()
                .unique();
        })
        .createTable('animals', tbl=> {
            tbl.increments();
            tbl.string('animal_name', 128);
            tbl.integer('species_id')
                .unsigned()
                .notNullable()
                .references('id')
                .inTable('species');
        })
        .createTable('zoo_animals', tbl => {
            tbl.integer('animal_id')
                .unsigned()
                .notNullable()
                .references('animals.id');
            tbl.integer('zoo_id')
                .unsigned()
                .notNullable()
                .references('zoos.id');
            tbl.primary(['zoo_id', 'animal_id']);
        })
    );
};