eager loading and lazy loading in rails

Question

I am confused about eager loading and lazy loading, is there any difference in the performance of rails queries?

Is there any way to implement both ways?

Answer 1

Eager loading

Loads your guns (like in Vicksburg) and just wait till you actually need to use it. This is a policy of eager loading.

Pro: is that everything's ready to go.

Con: you are using up space/memory.

Lazy Loading

A young naval cadet asked Lord Nelson why he wasn't preparing his ships:

"I won't load my guns early.......I'll load just 1 microsecond before I need to fire it." he said. This is a lazy loading policy.

Pro of lazy loading: you don't hit the database until you need to.

Con: You'll be hitting the database N + 1 times.....unless you select exactly the column you want and you alias it. e.g.

@products = Product.order("categories.name").joins(:category)

Hitting the Database only once with a lazy loading policy:

The above query hits the database N + 1 times when you call product.category.name in the view template - where product is a single object within the @products relation. But if you alias it, you can get everything done with just one query:

@products = Product.order("categories.name").joins(:category).select("products.*, categories.name as category_name")

And use it like this: product.category_name