defmodule TypedEctoSchema do
@moduledoc """
TypedEctoSchema provides a DSL on top of `Ecto.Schema` to define schemas with typespecs without
all the boilerplate code.
## Rationale
Normally, when defining an `Ecto.Schema` you probably want to define:
* the schema itself
* the list of enforced keys (which helps reducing problems)
* its associated type (`Ecto.Schema` doesn't define it for you)
It ends up in something like this:
defmodule Person do
use Ecto.Schema
@enforce_keys [:name]
schema "people" do
field(:name, :string)
field(:age, :integer)
field(:happy, :boolean, default: true)
field(:phone, :string)
belongs_to(:company, Company)
timestamps(type: :naive_datetime_usec)
end
@type t() :: %__MODULE__{
__meta__: Ecto.Schema.Metadata.t(),
id: integer() | nil,
name: String.t(),
age: non_neg_integer() | nil,
happy: boolean(),
phone: String.t() | nil,
company_id: integer() | nil,
company: Company.t() | Ecto.Association.NotLoaded.t() | nil,
inserted_at: NaiveDateTime.t(),
updated_at: NaiveDateTime.t()
}
end
This is problematic for a a lot of reasons, summing up:
- A lot of repetition. Field names appear in 3 different places, so in order to understand one
field, a reader needs to go up and down the code to get that.
- Ecto has some "hidden" fields that are added behind the scenes to the struct, such as the
primary key `id`, the foreign key `company_id`, the timestamps and the `__meta__` field for
schemas. Knowing all those rules can be hard to remember and would probably be easily
forgotten when changing the schema. Also, Ecto has strange types for associations and metadata that
need to be remembered.
All of this makes this process extremely repetitive and error prone. Sometimes, you want to
enforce factory functions to control defaults in a better way, you would probably add all fields
to `@enforce_keys`. This would make the `@enforce_keys` big and repetitive, once again.
This module aims to help with that, by providing some syntax sugar that allow you to define this
in a more compact way.
defmodule Person do
use TypedEctoSchema
typed_schema "people" do
field(:name, :string, enforce: true, null: false)
field(:age, :integer) :: non_neg_integer() | nil
field(:happy, :boolean, default: true, null: false)
field(:phone, :string)
belongs_to(:company, Company)
timestamps(type: :naive_datetime_usec)
end
end
This is way simpler and less error prone. There is a lot going under the hoods here.
## Extra Options
All ecto macros are called under the hood with the options you pass, with exception of a few
added options:
- `:null` - when `true`, adds a `| nil` to the typespec. Default is `true`. Has no effect on
`has_one/3` because it can always be `nil`. On `belongs_to/3` only add `| nil` to the
underlying foreign key.
- `:enforce` - when `true` adds the field to the `@enforce_keys`. Default is `false`
## Schema Options
When calling `typed_schema/3` or `typed_embedded_schema/2` you can pass some options, as
defined:
- `:null` - Set the default `:null` field option, which normally is true. Note that it is still
can be overwritten by passing `:null` to the field itself.
Also, `embeds_many` and `has_many` can never be null, because they are always initialized to
empty string, so they never receive the `| nil` on the typespec.
In addition to that, `has_one/3` and `belongs_to/3` always receive `| nil` because the related
schema may be deleted from the repo so it is safe to always assume they can be `nil`.
- `:enforce` - When `true`, enforces all fields unless they explicitly set `enforce: false` or
defines a default (`default: value`), since it makes no sense to have a default value for an
enforced field.
- `:opaque` - When `true` makes the generated type `t` be an opaque type.
## Type Inference
TypedEctoSchema does it's best job to guess the typespec for the field. It does so by following
the Elixir types as defined in [`Ecto.Schema`](https://hexdocs.pm/ecto/Ecto.Schema.html#module-primitive-types).
For custom `Ecto.Type` and related schemas (embedded and associations), which are always a
module, it assumes the schemas has a type `t/0` defined, so for a schema called `MySchema`, it
will assume the type is `MySchema.t/0`, which is also, the default type generated by this
library.
## Overriding the Typespec for a field
If for somereason you want to narrow the type or the automatic type inference is incorrect,
the `::` operator allows the typespec to be overriden.
This is done as you would when defining typespecs.
So, for example, instead of
```elixir
field(:my_int, :integer)
```
Which would generate a `integer() | nil` typespec, you can:
```elixir
field(:my_int, :integer) :: non_neg_integer() | nil
```
And then have a `non_neg_integer()` type for it.
## Non explicit generated fields
Ecto generates some fields for you in a lot of cases, they are:
- For primary keys
- When using a `belongs_to/3`
- When calling `timestamps/1`
The `__meta__` typespec is automatically generated and cannot be overriden. That is because
there is no point on overriding it.
### Primary Keys
Primary keys are generated by default and can be customized by the `@primary_key` module
attribute, just as defined by Ecto. We handle `@primary_key` the same way we handle `field/3`, so you
can pass the same field options to it.
However, if you want to customize the type, you need to set `@primary_key false` and define a
field with `primary_key: true`.
### Belongs To
`belongs_to` generates an underlying foreign key that is dependent on a few Ecto options, as
defined on [`Ecto.Schema`](https://hexdocs.pm/ecto/Ecto.Schema.html#belongs_to/3-options).
The options we are interested in are `:foreign_key`, `:define_field` and `:type`
When `:null` is passed, it will add `| nil` to the generated `foreign_key`'s typespec.
The `:enforce` option enforces the association field instead.
If you want to `:enforce` the foreign key to be set, you should probably pass `define_field:
false` and define the foreign key by hand, setting another `field/3`, the same way as
described by Ecto's doc.
### Timestamps
In the case of the timestamps, we currently don't allow overriding the type by using the `::` operator.
That being said, however, we define the type of the fields using the `:type` option
([as defined by Ecto doc](https://hexdocs.pm/ecto/Ecto.Schema.html#timestamps/1-options))
"""
alias TypedEctoSchema.SyntaxSugar
alias TypedEctoSchema.TypeBuilder
@doc false
defmacro __using__(_) do
quote do
import TypedEctoSchema,
only: [
typed_embedded_schema: 1,
typed_embedded_schema: 2,
typed_schema: 2,
typed_schema: 3
]
use Ecto.Schema
end
end
@doc """
Replaces `Ecto.Schema.embedded_schema/1`
"""
defmacro typed_embedded_schema(opts \\ [], do: block) do
quote do
unquote(prelude(opts))
Ecto.Schema.embedded_schema do
unquote(inner(block, __CALLER__))
end
unquote(postlude(opts))
end
end
@doc """
Replaces `Ecto.Schema.schema/2`
"""
defmacro typed_schema(table_name, opts \\ [], do: block) do
quote do
unquote(prelude(opts))
unquote(TypeBuilder).add_meta(__MODULE__)
Ecto.Schema.schema unquote(table_name) do
unquote(inner(block, __CALLER__))
end
unquote(postlude(opts))
end
end
defp prelude(opts) do
quote do
require unquote(TypeBuilder)
unquote(TypeBuilder).init(unquote(opts))
end
end
defp inner(block, env) do
quote do
unquote(TypeBuilder).add_primary_key(__MODULE__)
unquote(SyntaxSugar.apply_to_block(block, env))
unquote(TypeBuilder).enforce_keys()
end
end
defp postlude(opts) do
quote do
unquote(TypeBuilder).define_type(unquote(opts))
end
end
end