Question

What’s the preferred syntax for adding an index to a table in Rails via a migration?

Answer 1

The preferred syntax is:

add_index(table_name, column_names, options)

There is a full write up in the docs here. To find the relevant section, just do a ‘Ctrl-F’ (or equivalent on your OS) search for ‘index’. The first result is in the section you want to read over.

You can add in index in a separate migration later on, as shown in this post. Its a bit dated, but the idea is still the same. The most common ‘options’ are :name and :unique, for example

 { :name => "users_name_index", :unique => true }

Note: curly brackets are important, as the options are a hash.