Custom Data Types in Ecto

Talk for the Chicago Elixir Meetup in May/2017.

Ecto allows you create new data types that are not present out of box. This feature is very useful when your database has specific data types and you want to leverage it in your application.

As Ecto is a DSL and database wrapper, what happens often is that Ecto will cover all common data types but will not be covering all database specific data types.

In this talk I will cover how to create a data type in Ecto that will allow the application persist and retrieve ranges, a Postgres specific data type.

Transcript

1. How leverage the features your database provides. CUSTOM DATA TYPES IN ECTO CHICAGO ELIXIR MEETUP - MAY/2017
2. INTRODUCTION ➤ Pedro Assumpcao ➤ Senior Software Engineer at CityBase pedroassumpcao.ghost.io @pedroassumpcao |> github.com @pedroassumpcao |> twitter.com CHICAGO ELIXIR MEETUP - MAY/2017
3. AGENDA ➤ What problem we are trying to solve ➤ Context/Scenario ➤ How Ecto handles custom data types ➤ Creating a custom data type ➤ Querying a custom data type CHICAGO ELIXIR MEETUP - MAY/2017
4. WHAT PROBLEM WE ARE TRYING TO SOLVE ➤ Let's say we have two models: Product and Discount ➤ Product has price ➤ Discount has a percentage off based on a price range CHICAGO ELIXIR MEETUP - MAY/2017
5. WHAT PROBLEM WE ARE TRYING TO SOLVE ➤ Let's say we have two models: Product and Discount ➤ Product has price ➤ Discount has a percentage off based on a price range ➤ Our first attempt is in the Discount model: ➤ minimum_price ➤ maximum_price CHICAGO ELIXIR MEETUP - MAY/2017
7. WHAT PROBLEM WE ARE TRYING TO SOLVE ➤ We should avoid queries like this: ➤ List percentage_off for a product price of $65: SELECT percentage_off FROM discounts WHERE mininum_price <= 65 and maximum_price >= 65; CHICAGO ELIXIR MEETUP - MAY/2017
8. WHAT PROBLEM WE ARE TRYING TO SOLVE ➤ List all records based on a price range of $100 and $250: SELECT * FROM discounts WHERE (minimum_price < 100 AND maximum_price > 250) OR (minimum_price between 100 and 250) OR (maximum_price between 100 and 250); CHICAGO ELIXIR MEETUP - MAY/2017
9. HOW CAN WE DO THIS IN A BETTER WAY? CHICAGO ELIXIR MEETUP - MAY/2017
10. CONTEXT/SCENARIO ➤ Postgres 9.2 introduced Range Types: ➤ int4range — Range of integer ➤ int8range — Range of bigint ➤ numrange — Range of numeric ➤ tsrange — Range of timestamp without time zone ➤ tstzrange — Range of timestamp with time zone ➤ daterange — Range of date CHICAGO ELIXIR MEETUP - MAY/2017
11. CONTEXT/SCENARIO ➤ Some range representation examples in Postgres: ➤ [2,14] => 2 ≤ x ≤ 14 ➤ [2, 14) => 2 ≤ x < 14 ➤ (2,14] => 2 < x ≤ 14 ➤ (2,14) => 2 < x < 14 ➤ [2,) => 2 ≤ x < ∞ ➤ (,2] => -∞ < x ≤ 2 CHICAGO ELIXIR MEETUP - MAY/2017
12. CONTEXT/SCENARIO ➤ Some examples of querying range types: ➤ List percentage_off for a product price of $65: SELECT percentage_off FROM discounts WHERE 65::numeric <@ price_range; ➤ List all records based on a price range of $100 and $250: SELECT * FROM discounts WHERE discounts.price_range && int4range(100, 250, '[]'); CHICAGO ELIXIR MEETUP - MAY/2017
13. IN ELIXIR WORLD... CHICAGO ELIXIR MEETUP - MAY/2017
14. CONTEXT/SCENARIO ➤ Ecto is the database wrapper and DSL for queries ➤ Ecto works with database adapters: ➤ postgrex (Postgres) ➤ mariex (MySql) ➤ msql_ecto (MSSql) ➤ and others ➤ Each adapter knows better the database features and specifics CHICAGO ELIXIR MEETUP - MAY/2017
15. CONTEXT/SCENARIO ➤ Ecto only provides the most common data types: ➤ id, binary_id, uuid ➤ integer, float, decimal ➤ string, binary ➤ boolean ➤ date, time, utc_datetime ➤ list, map CHICAGO ELIXIR MEETUP - MAY/2017
17. ECTO.TYPE BEHAVIOUR CHICAGO ELIXIR MEETUP - MAY/2017
18. WHAT IS A BEHAVIOUR? ➤ Separates the generic part (the behaviour module) of a component from the specific part (the callback module) ➤ Perfect when modules share the same public API ➤ A behaviour module defines a set of functions ➤ The callback module implements them CHICAGO ELIXIR MEETUP - MAY/2017
19. CREATING A CUSTOM TYPE ➤ Ecto provides a behaviour called Ecto.Type: CHICAGO ELIXIR MEETUP - MAY/2017
20. CREATING A CUSTOM TYPE type/0 ➤ outputs the name of the database type CHICAGO ELIXIR MEETUP - MAY/2017
21. CREATING A CUSTOM TYPE cast/1 ➤ receives any term and validates CHICAGO ELIXIR MEETUP - MAY/2017
22. CREATING A CUSTOM TYPE load/1 ➤ loads the data from the adapter and outputs the custom type CHICAGO ELIXIR MEETUP - MAY/2017
23. CREATING A CUSTOM TYPE dump/1 ➤ receives a validated data and outputs an adapter type CHICAGO ELIXIR MEETUP - MAY/2017
24. USING A CUSTOM TYPE ➤ Migrations: CHICAGO ELIXIR MEETUP - MAY/2017
25. USING A CUSTOM TYPE ➤ Schemas: CHICAGO ELIXIR MEETUP - MAY/2017
26. QUERYING A CUSTOM TYPE ➤ Using fragment/1 you can perform any range specific operation that Postgres offers: CHICAGO ELIXIR MEETUP - MAY/2017
27. SUMMARY ➤ Postgres has data types that help us model properly ➤ Database adapters are close to the database features ➤ Ecto gives us flexibility to create our own types if we need ➤ Querying customized data types is easy CHICAGO ELIXIR MEETUP - MAY/2017
28. FURTHER READING ➤ https://www.postgresql.org/docs/9.6/static/rangetypes.html ➤ http://pedroassumpcao.ghost.io/using-postgres-range-data-type-in-ecto/ ➤ https://hexdocs.pm/ecto/Ecto.Type.html ➤ https://github.com/elixir-ecto/postgrex#data-representation CHICAGO ELIXIR MEETUP - MAY/2017
29. QUESTIONS? CHICAGO ELIXIR MEETUP - MAY/2017
30. THANKS! CHICAGO ELIXIR MEETUP - MAY/2017