.find或活动记录查询中的条件

Question

I am confused on where to use '.find' and where to use 'where'. is there a difference in the performance during the execution of the query ??

example : converted the existing queries which are using .find as below :

FileOrFolder.find_by_fullpath(completePath, :select=>"id") -->

FileOrFolder.where(fullpath: completePath).select(:id).first

Component.find(:first, :conditions=>["cluster_id = ? AND name = ?", cluster_id, key]) -->

Component.where(cluster_id: cluster_id, name: key).first

Answer 1

These are all equivalent. What you're seeing here is the evolution of the ActiveRecord query syntax from before AREL was incorporated. The older style dynamic finders are still valid, though.

This syntax is from ROR 2.x and earlier using dynamic finders:

FileOrFolder.find_by_fullpath(completePath, :select=>"id")

Whereas these are more in the ROR 3.x style:

FileOrFolder.where(fullpath: completePath).select(:id).first
Component.where(cluster_id: cluster_id, name: key).first

And your last example using find is valid in either context.

Component.find(:first, :conditions=>["cluster_id = ? AND name = ?", cluster_id, key])

When in doubt, consult the ROR query guide .

I personally find the where styles are very useful when you're building up a query over several lines of code and not all at once. Since they defer execution until the latest moment, they let you build the query piecemeal.

Answer 2

It doesn't make a significant performance difference because usually they will both generate the same SQL, eg:

Article.find_by_headline('foo')
=> SELECT `articles`.* FROM `articles` WHERE `articles`.`headline` = 'foo' LIMIT 1

Article.where(headline: 'foo').first
=> SELECT `articles`.* FROM `articles` WHERE `articles`.`headline` = 'foo' LIMIT 1

Answer 3

你应该更喜欢where的风格前进，轨道4,5已否决使用find_by_ -见http://edgeguides.rubyonrails.org/4_0_release_notes.html#active-record-deprecations