Programming Ecto

Building on Top of Ecto’s Types

When we talked about schemas, we had a table that showed how Ecto’s types map to an Elixir type. If you use :string, for example, when defining a field, Ecto treats the value as a String on the Elixir side, then uses whatever column definition your database uses to store string values.

But if you think about it, a number of different kinds of data can be stored as a string: a date, a UUID, a list of values, even a complex collection of data in JSON. All of these can be stored as a string, but then parsed into a more meaningful type when brought into Elixir. Our first look at creating custom types handles this exact case: taking a value stored as a simple type in the database, and turning it into a different type ...