Dynamic Finders
For every field (also known as an attribute) you define in your table, Active Record provides a finder method. If you have a field called name on your Client model for example, you get find_by_name and find_all_by_name for free from Active Record. If you have also have a locked field on the Client model, you also get find_by_locked and find_all_by_locked.
You can do find_last_by_* methods too which will find the last record matching your argument.
You can specify an exclamation point (!) on the end of the dynamic finders to get them to raise an ActiveRecord::RecordNotFound error if they do not return any records, like Client.find_by_name!("Ryan")
If you want to find both by name and locked, you can chain these finders together by simply typing and between the fields for example Client.find_by_name_and_locked("Ryan", true).
There’s another set of dynamic finders that let you find or create/initialize objects if they aren’t found. These work in a similar fashion to the other finders and can be used like find_or_create_by_name(params[:name]). Using this will firstly perform a find and then create if the find returns nil. The SQL looks like this for Client.find_or_create_by_name("Ryan"):
SELECT * FROM clients WHERE (clients.name = 'Ryan') LIMIT 1
BEGIN
INSERT INTO clients (name, updated_at, created_at, orders_count, locked)
VALUES('Ryan', '2008-09-28 15:39:12', '2008-09-28 15:39:12', 0, '0')
COMMIT
find_or_create’s sibling, find_or_initialize, will find an object and if it does not exist will act similar to calling new with the arguments you passed in. For example:
client = Client.find_or_initialize_by_name('Ryan')
will either assign an existing client object with the name “Ryan” to the client local variable, or initialize a new object similar to calling Client.new(:name => 'Ryan'). From here, you can modify other fields in client by calling the attribute setters on it: client.locked = true and when you want to write it to the database just call save on it.
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