What's the difference between the build and create methods in FactoryGirl?

Question

The Factory Girl introduction delineates the difference between FactoryGirl.build() and FactoryGirl.create():

# Returns a User instance that's not saved user = FactoryGirl.build(:user)  # Returns a saved User instance user = FactoryGirl.create(:user) 

I still doesn't understand the practical differences between the two. Can someone give an example where you would want to use one and not the other? Thanks!

Answer 1

The create() method persists the instance of the model while the build() method keeps it only on memory.

Personally, I use the create() method only when persistence is really necessary since writing to DB makes testing time consuming.

e.g.

I create users to authentication with create() because my authentication engine queries the DB.

To check if a model has an attribute the build() method will do because no DB access is required.

it{Factory.build(:user).should respond_to(:name)} 

Update

"There is one exception that build actually 'creates' when you are building associations, i.e your association are no longer in memory but persisted. Keep that in mind" – Shakes

Answer 2

Using FactoryGirl.build(:factory_name) does not persist to the db and does not call save!, so your Active Record validations will not run. This is much faster, but validations might be important.

Using FactoryGirl.create(:factory_name) will persist to the db and will call Active Record validations. This is obviously slower but can catch validation errors (if you care about them in your tests).