Counter to keep track of references?

rubyonrails-talk
1

Hi,

I'd like to ask something. I have messages and I have countries. I do searches of messages by country. So a country has_many messages and message belongs_to country.

I have defined a country_id on the messages country.

Is there a quick way to find how many messages belong to a country without going through the messages find? I thought of adding a counter to the country table and increase/decrease when a message for that country is handled. Is this the right approach?

Thanks.

2

if you have that defined the Rails way with has_many, then:

@country.messages.size

would give you that number.

You can enhance speed for that, by using

has_many :messages, :counter_cache => true

in countries model. This would require a column messages_count in countries

3

Also, @country.messages.count will do an SQL COUNT query and return
it. Thorsten's suggestion is quicker of course since you're only
performing one query.

4

Thanks a lot guys!