ActiveRecord: adding children to a has_many parent

rubyonrails-talk
1

given parent.list is a has_many of Child, I've found that if I do this:

    child = Child.new(...)     parent.list << child

rails will select * all of parent.list before doing the insert of the new child (if parent.list isn't already loaded). This is -bad- because my parent.list is huge.

So instead, I do this:

    child = Child.new(...)     child.parent = parent     child.save!

This ensures a single insert and also throws an exception if any DB constraints are violated, thus ensuring any encompassing transactions and/or top level logging is handled.

is this generally the right thing to do with rails? I'm a noob coming from enterprise development in other languages.

Or is there some other magic way to add to parent.list with the above kind behavior?

2

bataras wrote:

given parent.list is a has_many of Child, I've found that if I do this:

   child = Child.new(...)    parent.list << child

rails will select * all of parent.list before doing the insert of the new child (if parent.list isn't already loaded). This is -bad- because my parent.list is huge.

So instead, I do this:

   child = Child.new(...)    child.parent = parent    child.save!

The most terse way would be

   parent.list.create(...)

If you want to defer saving you can instead use the "build" method.

3

Cool. Thanks. I'll use that. In one case though, I have to create a new child that "belongs_to" 2 different kinds of parents. So for that, I'll have to use the build method to make it happen in a single insert.