defmodule Ecto.ParameterizedType do
@moduledoc """
Parameterized types are Ecto types that can be customized per field.
Parameterized types allow a set of options to be specified in the schema
which are initialized on compilation and passed to the callback functions
as the last argument.
For example, `field :foo, :string` behaves the same for every field.
On the other hand, `field :foo, Ecto.Enum, values: [:foo, :bar, :baz]`
will likely have a different set of values per field.
Note that options are specified as a keyword, but it is idiomatic to
convert them to maps inside `c:init/1` for easier pattern matching in
other callbacks.
Parameterized types are a superset of regular types. In other words,
with parameterized types you can do everything a regular type does,
and more. For example, parameterized types can handle `nil` values
in both `load` and `dump` callbacks, they can customize `cast` behavior
per query and per changeset, and also control how values are embedded.
However, parameterized types are also more complex. Therefore, if
everything you need to achieve can be done with basic types, they
should be preferred to parameterized ones.
## Examples
To create a parameterized type, create a module as shown below:
defmodule MyApp.MyType do
use Ecto.ParameterizedType
def type(_params), do: :string
def init(opts) do
validate_opts(opts)
Enum.into(opts, %{})
end
def cast(data, params) do
...
{:ok, cast_data}
end
def load(data, _loader, params) do
...
{:ok, loaded_data}
end
def dump(data, dumper, params) do
...
{:ok, dumped_data}
end
def equal?(a, b, _params) do
a == b
end
end
To use this type in a schema field, specify the type and parameters like this:
schema "foo" do
field :bar, MyApp.MyType, opt1: :baz, opt2: :boo
end
To use this type in places where you need it to be initialized (for example,
schemaless changesets), you can use `init/2`.
> #### `use Ecto.ParameterizedType` {: .info}
>
> When you `use Ecto.ParameterizedType`, it will set
> `@behaviour Ecto.ParameterizedType` and define default, overridable
> implementations for `c:embed_as/2` and `c:equal?/3`.
"""
@typedoc """
The keyword options passed from the Schema's field macro into `c:init/1`
"""
@type opts :: keyword()
@typedoc """
The parameters for the ParameterizedType
This is the value passed back from `c:init/1` and subsequently passed
as the last argument to all callbacks. Idiomatically it is a map.
"""
@type params :: term()
@doc """
Callback to convert the options specified in the field macro into parameters
to be used in other callbacks.
This function is called at compile time, and should raise if invalid values are
specified. It is idiomatic that the parameters returned from this are a map.
`field` and `schema` will be injected into the options automatically.
For example, this schema specification
schema "my_table" do
field :my_field, MyParameterizedType, opt1: :foo, opt2: nil
end
will result in the call:
MyParameterizedType.init([schema: "my_table", field: :my_field, opt1: :foo, opt2: nil])
"""
@callback init(opts :: opts()) :: params()
@doc """
Casts the given input to the ParameterizedType with the given parameters.
If the parameterized type is also a composite type,
the inner type can be cast by calling `Ecto.Type.cast/2`
directly.
For more information on casting, see `c:Ecto.Type.cast/1`.
"""
@callback cast(data :: term, params()) ::
{:ok, term} | :error | {:error, keyword()}
@doc """
Loads the given term into a ParameterizedType.
It receives a `loader` function in case the parameterized
type is also a composite type. In order to load the inner
type, the `loader` must be called with the inner type and
the inner value as argument.
For more information on loading, see `c:Ecto.Type.load/1`.
Note that this callback *will* be called when loading a `nil`
value, unlike `c:Ecto.Type.load/1`.
"""
@callback load(value :: any(), loader :: function(), params()) :: {:ok, value :: any()} | :error
@doc """
Dumps the given term into an Ecto native type.
It receives a `dumper` function in case the parameterized
type is also a composite type. In order to dump the inner
type, the `dumper` must be called with the inner type and
the inner value as argument.
For more information on dumping, see `c:Ecto.Type.dump/1`.
Note that this callback *will* be called when dumping a `nil`
value, unlike `c:Ecto.Type.dump/1`.
"""
@callback dump(value :: any(), dumper :: function(), params()) :: {:ok, value :: any()} | :error
@doc """
Returns the underlying schema type for the ParameterizedType.
For more information on schema types, see `c:Ecto.Type.type/0`
"""
@callback type(params()) :: Ecto.Type.t()
@doc """
Checks if two terms are semantically equal.
"""
@callback equal?(value1 :: any(), value2 :: any(), params()) :: boolean()
@doc """
Dictates how the type should be treated inside embeds.
For more information on embedding, see `c:Ecto.Type.embed_as/1`
"""
@callback embed_as(format :: atom(), params()) :: :self | :dump
@doc """
Generates a loaded version of the data.
This callback is invoked when a parameterized type is given
to `field` with the `:autogenerate` flag.
"""
@callback autogenerate(params()) :: term()
@doc """
Formats output when a ParameterizedType is printed in exceptions and
other logs.
Note this callback is not used when constructing `Ecto.Changeset` validation
errors. See the `:message` option of most `Ecto.Changeset` validation
functions for how to customize error messaging on a per `Ecto.Changeset` basis.
"""
@callback format(params()) :: String.t()
@optional_callbacks autogenerate: 1, format: 1
@doc """
Inits a parameterized type given by `type` with `opts`.
Useful when manually initializing a type for schemaless changesets.
"""
def init(type, opts) do
{:parameterized, type, type.init(opts)}
end
@doc false
defmacro __using__(_) do
quote location: :keep do
@behaviour Ecto.ParameterizedType
@doc false
def embed_as(_, _), do: :self
@doc false
def equal?(term1, term2, _params), do: term1 == term2
defoverridable embed_as: 2, equal?: 3
end
end
end
