Getting Started on Elixir and Ecto Part 3

Schema, Changeset and Data types

At this point, you might start to wonder why you are doing essentially the same thing twice when dealing with Schema and Changeset.

While migrations are liable for giving us the database tables, schemas are liable for how Ecto interacts with those tables.

A schema is an Elixir declaration of data from our database. Besides working as data mappers, embedded_schema/1 and schema/2 can also be used together to decouple how the data is represented in your applications from the database.

schema/2 is typically used to map data from a persisted source, usually a database table, into Elixir structs and vice-versa.

embedded_schema/1 is used for defining schemas that are embedded in other schemas or only exist in memory without ever persisting elsewhere.

Changesets define a pipeline of transformations our data needs to undergo before it will be ready for our application to use. These transformations might include type-casting, user input validation, and filtering out any extraneous parameters.

NOTE: You can actually use an embedded schema to depict your UI, mapping and validating its inputs, and then you convert such embedded schema to other schemas that can persist data to the database.

NOTE: The naming convention in Ecto for schemas is a singularized name.

ECTO TYPE  -> ELIXIR TYPE  -> LITERAL SYNTAX IN QUERY

:id -> integer  { 1, 2, ...}
:binary_id -> binary  { <<int, int, ...>> }
:integer -> integer  { 1, 2, ...}
:float -> float  { 1.0, 2.0, ... }
:boolean -> boolean  { true, false }
:string -> UTF-8 encoded string  { "hello" }
:binary -> binary { int, int, ... }
{:array, inner_type} -> list { [value, value, ...] }
:map -> map
{:map, inner_type} -> map
:decimal -> Decimal
:date -> Date
:time -> Time
:time_usec -> Time
:naive_datetime -> NaiveDateTime
:naive_datetime_usec -> NaiveDateTime
:utc_datetime -> DateTime
:utc_datetime_usec -> DateTime

You can easily play around with schema by simply starting an IEx iex -S mix

task = %Taskers.Task{}

We can set values on these fields by generating a new struct:
task = %Taskers.Task{estimated_time: 28}
task = %{task | estimated_time: 3.0}

And retrieve values using this syntax:
task.estimated_time # => 3.0