find vs find_by vs where

Question

I am new to rails. What I see that there are a lot of ways to find a record:

1. find_by_<columnname>(<columnvalue>)
2. find(:first, :conditions => { <columnname> => <columnvalue> }
3. where(<columnname> => <columnvalue>).first

And it looks like all of them end up generating exactly the same SQL. Also, I believe the same is true for finding multiple records:

1. find_all_by_<columnname>(<columnvalue>)
2. find(:all, :conditions => { <columnname> => <columnvalue> }
3. where(<columnname> => <columnvalue>)

Is there a rule of thumb or recommendation on which one to use?

Answer 1

where returns ActiveRecord::Relation

Now take a look at find_by implementation:

def find_by
  where(*args).take
end

As you can see find_by is the same as where but it returns only one record. This method should be used for getting 1 record and where should be used for getting all records with some conditions.

Answer 2

Edit: This answer is very old and other, better answers have come up since this post was made. I'd advise looking at the one posted below by @Hossam Khamis for more details.

Use whichever one you feel suits your needs best.

The find method is usually used to retrieve a row by ID:

Model.find(1)

It's worth noting that find will throw an exception if the item is not found by the attribute that you supply. Use where (as described below, which will return an empty array if the attribute is not found) to avoid an exception being thrown.

Other uses of find are usually replaced with things like this:

Model.all
Model.first

find_by is used as a helper when you're searching for information within a column, and it maps to such with naming conventions. For instance, if you have a column named name in your database, you'd use the following syntax:

Model.find_by(name: "Bob")

.where is more of a catch all that lets you use a bit more complex logic for when the conventional helpers won't do, and it returns an array of items that match your conditions (or an empty array otherwise).