How to get the count of unsaved associated records? [duplicate]

Question

Given these ActiveRecord table definitions:

create_table :parents do |t|
end

create_table :children do |t|
  t.references :parent
end

And the corresponding models:

class Parent < ActiveRecord::Base
  has_many :children
end

class Child < ActiveRecord::Base
  belongs_to :parent 
end

When I create an unsaved record which has an unsaved association:

parent = Parent.new
parent.children << Child.new

And ask for the number of associated records:

parent.children.count
=> 0

Then the result is 0. I expected 1.

I wish for the count I get to reflect both unsaved and saved associated records. How can I get that count?

---

Versions:

• Rails 4.2.6
• Ruby 2.3.3

Answer 1

You need to use #size rather than #count. As you (well, I) discovered, #count ignores records in memory. #size considers both saved and unsaved records.

Here are the methods you can use to test for the existence or count of associated records:

count

count only considers what in the database, ignoring anything in memory. This issues an SQL statement every time, ignoring any caching.

size

To get the total number of saved and unsaved associated records, use size. This method differs from length in that it does not force associated records to be loaded into memory.

length

To load all associated records into memory and then count all records, use length. The total count of both saved and unsaved records will be returned.

exists?

To find out if there are any records on disk, ignoring the presence of any in memory, use exists?. This issues an SQL statement every time, ignoring any caching.

References

a github comment by Carlos Antonio Dasilva:

• length with always load the objects and use Array#length

• count will always do a SQL count

• size will check whether the collection is loaded, and use it, otherwise will do a count.

size should give you the correct value in this case I think.