Saving multiple objects in a single call in rails

Question

I have a method in rails that is doing something like this:

a = Foo.new("bar")
a.save

b = Foo.new("baz")
b.save

...
x = Foo.new("123", :parent_id => a.id)
x.save

...
z = Foo.new("zxy", :parent_id => b.id)
z.save

The problem is this takes longer and longer the more entities I add. I suspect this is because it has to hit the database for every record. Since they are nested, I know I can't save the children before the parents are saved, but I would like to save all of the parents at once, and then all of the children. It would be nice to do something like:

a = Foo.new("bar")
b = Foo.new("baz")
...
saveall(a,b,...)

x = Foo.new("123", :parent_id => a.id)
...
z = Foo.new("zxy", :parent_id => b.id)
saveall(x,...,z)

That would do it all in only two database hits. Is there an easy way to do this in rails, or am I stuck doing it one at a time?

Answer 1

You might try using Foo.create instead of Foo.new. Create "Creates an object (or multiple objects) and saves it to the database, if validations pass. The resulting object is returned whether the object was saved successfully to the database or not."

You can create multiple objects like this:

# Create an Array of new objects
  parents = Foo.create([{ :first_name => 'Jamie' }, { :first_name => 'Jeremy' }])

Then, for each parent, you can also use create to add to its association:

parents.each do |parent|
  parent.children.create (:child_name => 'abc')
end

I recommend reading both the ActiveRecord documentation and the Rails Guides on ActiveRecord query interface and ActiveRecord associations. The latter contains a guide of all the methods a class gains when you declare an association.

Answer 2

Since you need to perform multiple inserts database will be hit multiple times. The delay in your case is because each save is done in different DB transactions. You can reduce the latency by enclosing all your operations in one transaction.

class Foo
  belongs_to  :parent,   :class_name => "Foo"
  has_many    :children, :class_name => "Foo", :foreign_key=> "parent_id"
end

Your save method might look like this:

# build the parent and the children
a = Foo.new(:name => "bar")
a.children.build(:name => "123")

# build the parent and the children
b = Foo.new("baz")
b.children.build(:name => "zxy")

#save parents and their children in one transaction
Foo.transaction do
  a.save
  b.save
end

The save call on the parent object saves the child objects.