Where do you specify data relationships?
How much effort does Rails put into enforcing relationships between models?
What does the
collect method do?
How can you check to see whether a related record exists?
Why would you want to go to the trouble of creating a nested resource?
When would you use a
form_for do when it is passed an
array for its first argument?
What two columns are needed in a join table?
Why would you want to index the columns of a join table?
Where do you tell Rails about new methods you’ve added to the scaffolding?
Relationships are specified in models. The models on both sides of any given
relationship must identify how they relate to
the other model. For example, a
relationship in one model should be matched by a
belongs_to relationship in another model.
Rails doesn’t put any effort into enforcing relationships between models. If you have constraints to impose, you need to create code that checks and enforces them.
collect method iterates over a collection and gathers the results from a block.
It’s an easy way to turn a list of data into a
select list, for instance.
You could check for a related record with
but in most validation contexts it’s easier to use the
validates_existence_of plug-in. (If you want to check for a related
valid record, then Rails’ built-in
validates_associated will work.)
Nested resources have some programming aesthetic appeal, but they’re also useful for making relationships ...