Rails 4: List of available datatypes

Here are all the Rails 4 (ActiveRecord migration) datatypes:

• :binary
• :boolean
• :date
• :datetime
• :decimal
• :float
• :integer
• :bigint
• :primary_key
• :references
• :string
• :text
• :time
• :timestamp

Source: http://api.rubyonrails.org/classes/ActiveRecord/ConnectionAdapters/SchemaStatements.html#method-i-add_column
These are the same as with Rails 3.

If you use PostgreSQL, you can also take advantage of these:

• :hstore
• :json
• :jsonb
• :array
• :cidr_address
• :ip_address
• :mac_address

They are stored as strings if you run your app with a not-PostgreSQL database.

More PostgreSQL data types

• Rails 4
• Rails 5
• Rails 6
• Rails 7

It is important to know not only the types but the mapping of these types to the database types, too:

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Source added - Agile Web Development with Rails 4

You might also find it useful to know generally what these data types are used for:

• :string - is for small data types such as a title. (Should you choose string or text?)
• :text - is for longer pieces of textual data, such as a paragraph of information
• :binary - is for storing data such as images, audio, or movies.
• :boolean - is for storing true or false values.
• :date - store only the date
• :datetime - store the date and time into a column.
• :time - is for time only
• :timestamp - for storing date and time into a column.(What's the difference between datetime and timestamp?)
• :decimal - is for decimals (example of how to use decimals).
• :float - is for decimals. (What's the difference between decimal and float?)
• :integer - is for whole numbers.
• :primary_key - unique key that can uniquely identify each row in a table

There's also references used to create associations. But, I'm not sure this is an actual data type.

New Rails 4 datatypes available in PostgreSQL:

• :hstore - storing key/value pairs within a single value (learn more about this new data type)
• :array - an arrangement of numbers or strings in a particular row (learn more about it and see examples)
• :cidr_address - used for IPv4 or IPv6 host addresses
• :inet_address - used for IPv4 or IPv6 host addresses, same as cidr_address but it also accepts values with nonzero bits to the right of the netmask
• :mac_address - used for MAC host addresses

Learn more about the address datatypes here and here.

Also, here's the official guide on migrations: http://edgeguides.rubyonrails.org/migrations.html