# Factories & Building

First we'll learn how to create factories and how to use them to build entities. Let's say our application has users that we want to create for use in our tests, and each user has:

* a name
* an email
* a role - one of 'admin' or 'user'

We might write our factory definition as:

```clojure
(ns fab.tutorial
  (:require [fabrikk.core.alpha :as fab]))

(def user
  (fab/->factory
    ::user
    {:template {:name "John Smith"
                :email "john@example.org"
                :role "admin"}}) 
```

To create a factory we need an `id` and a factory definition; a map with at least a `template` key:

* The id is a keyword that uniquely identifies the factory, namespaced keywords are recommended. Fabrikk accepts factory ids and instances interchangeably in most places (see [#greater-than-factory](https://deadeyejoe.gitbook.io/fabrikk/reference/api#greater-than-factory "mention") for more)
* The template details the keys that our entity will have, and the values of those keys

We'll explore more options in the course of this tutorial, and you can take a look at [#factory-definition](https://deadeyejoe.gitbook.io/fabrikk/reference/api#factory-definition "mention") to see a comprehensive list.

Now that we have a  factory we can get building:

```clojure
(fab/build user) 
;; => {:name "John Smith", :email "john@example.org", :role "admin"}
(fab/build user) 
;; => {:name "John Smith", :email "john@example.org", :role "admin"}
```

But wait, this generates the same user every time! We can pass *build options* to `build` to vary the output, using the `with` option:

```clojure
;; we use 'with' to change the name:
(fab/build user {:with {:name "John Murphy"}})
;; => {:name "John Murphy", :email "john@example.org", :role "admin"}

;; or add an arbitrary key to the entity:
(fab/build user {:with {:favourite-food "chips"}})
;; => {:name "John Smith", :email "john@example.org", :role "admin", 
;;     :favourite-food "chips"}
```