Building on Top of Ecto’s Types

Map Ecto’s types

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

If we think about it, several different kinds of data can be stored as a string, such as a date, a UUID, a list of values, or even a complex data collection in JSON. These can be stored as a string and later parsed into a more meaningful type when brought into Elixir. In our first look at creating custom types, we take a value stored as a simple type in the database and turn it into a different kind when brought into Elixir.

Create a custom datetime type

We’d like to add support for working with dates and times in the Unix time format. We know that Ecto’s datetime type can store and retrieve timestamps to and from the database, but this type cannot handle the Unix format. We can cast strings in ISO-8601 format (2017-11-05T20:49:41Z), but if we tried to give it something like Date(1509914981), it wouldn’t work.

To make this work, we can create a custom type built on Ecto’s datetime type and create a slightly smarter version. To add our custom type, we need to create a module that implements the Ecto.Type behavior, which looks like the following.