In Ruby on Rails, all.each and for_each are both used to iterate over collections. Still, they have different use cases and characteristics:

all.each:

• all is a method commonly used on ActiveRecord relations, which returns all the records.
• each is a Ruby method that is used to iterate over an array or a collection.
• When you chain all.each, it first fetches all the records from the database into memory. Then it iterates over each record one by one.
• This can be memory-intensive if the dataset is large because it loads all records into memory at once.

Example:

User.all.each do |user|

  puts user.name

end

for_each:

• find_each is a method provided by ActiveRecord in Rails, which is used to retrieve records in batches and then iterate over each record. If you meant find_each when referring to for_each, this applies.
• It is more efficient for large datasets because it doesn’t load all records into memory at once. Instead, it loads them in batches (default batch size is 1000).
• This method is preferred for batch-processing tasks.

Example:

User.find_each do |user|

  puts user.name

end

Summary:

 If you are working with large datasets and want to avoid memory issues, find_each (or for_each if you meant that) is preferable. For smaller datasets or when you need all the records in memory for processing, all.each is sufficient.