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Ecto.Type behaviour

Defines functions and the Ecto.Type behaviour for implementing basic custom types.

Ecto provides two types of custom types: basic types and parameterized types. Basic types are simple, requiring only four callbacks to be implemented, and are enough for most occasions. Parameterized types can be customized on the field definition and provide a wilder variety of callbacks.

The definition of basic custom types and all of its callbacks is available in this module. You can learn more about parameterized types in Ecto.ParameterizedType. If in doubt, prefer to use basic custom types and rely on parameterized types if you need the extra functionality.

Example

Imagine you want to store an URI struct as part of a schema in an url-shortening service. There isn't an Ecto field type to support that value at runtime, therefore a custom one is needed.

You also want to query not only by the full url, but for example by specific ports used. This is possible by putting the URI data into a map field instead of just storing the plain string representation.

from s in ShortUrl,
  where: fragment("?->>? ILIKE ?", s.original_url, "port", "443")

So the custom type does need to handle the conversion from external data to runtime data (cast/1) as well as transforming that runtime data into the :map Ecto native type and back (dump/1 and load/1).

defmodule EctoURI do
  use Ecto.Type
  def type, do: :map

  # Provide custom casting rules.
  # Cast strings into the URI struct to be used at runtime
  def cast(uri) when is_binary(uri) do
    {:ok, URI.parse(uri)}
  end

  # Accept casting of URI structs as well
  def cast(%URI{} = uri), do: {:ok, uri}

  # Everything else is a failure though
  def cast(_), do: :error

  # When loading data from the database, as long as it's a map,
  # we just put the data back into an URI struct to be stored in
  # the loaded schema struct.
  def load(data) when is_map(data) do
    data =
      for {key, val} <- data do
        {String.to_existing_atom(key), val}
      end
    {:ok, struct!(URI, data)}
  end

  # When dumping data to the database, we *expect* an URI struct
  # but any value could be inserted into the schema struct at runtime,
  # so we need to guard against them.
  def dump(%URI{} = uri), do: {:ok, Map.from_struct(uri)}
  def dump(_), do: :error
end

Now we can use our new field type above in our schemas:

defmodule ShortUrl do
  use Ecto.Schema

  schema "posts" do
    field :original_url, EctoURI
  end
end

Note: nil values are always bypassed and cannot be handled by custom types.

Custom types and primary keys

Remember that, if you change the type of your primary keys, you will also need to change the type of all associations that point to said primary key.

Imagine you want to encode the ID so they cannot enumerate the content in your application. An Ecto type could handle the conversion between the encoded version of the id and its representation in the database. For the sake of simplicity we'll use base64 encoding in this example:

defmodule EncodedId do
  use Ecto.Type

  def type, do: :id

  def cast(id) when is_integer(id) do
    {:ok, encode_id(id)}
  end
  def cast(_), do: :error

  def dump(id) when is_binary(id) do
    Base.decode64(id)
  end

  def load(id) when is_integer(id) do
    {:ok, encode_id(id)}
  end

  defp encode_id(id) do
    id
    |> Integer.to_string()
    |> Base.encode64
  end
end

To use it as the type for the id in our schema, we can use the @primary_key module attribute:

defmodule BlogPost do
  use Ecto.Schema

  @primary_key {:id, EncodedId, autogenerate: true}
  schema "posts" do
    belongs_to :author, Author, type: EncodedId
    field :content, :string
  end
end

defmodule Author do
  use Ecto.Schema

  @primary_key {:id, EncodedId, autogenerate: true}
  schema "authors" do
    field :name, :string
    has_many :posts, BlogPost
  end
end

The @primary_key attribute will tell ecto which type to use for the id.

Note the type: EncodedId option given to belongs_to in the BlogPost schema. By default, Ecto will treat associations as if their keys were :integers. Our primary keys are a custom type, so when Ecto tries to cast those ids, it will fail.

Alternatively, you can set @foreign_key_type EncodedId after @primary_key to automatically configure the type of all belongs_to fields.

Summary

Types

custom()

Custom types are represented by user-defined modules.

primitive()

Primitive Ecto types (handled by Ecto).

t()

An Ecto type, primitive or custom.

Functions

base?(atom)

Checks if the given atom can be used as base type.

cast(type, value)

Casts a value to the given type.

composite?(atom)

Checks if the given atom can be used as composite type.

dump(type, value, dumper \\ &dump/2)

Dumps a value to the given type.

embed_as(base, format)

Gets how the type is treated inside embeds for the given format.

embedded_dump(type, value, format)

Dumps the value for type considering it will be embedded in format.

embedded_load(type, value, format)

Loads the value for type considering it was embedded in format.

equal?(type, term1, term2)

Checks if two terms are equal.

load(type, value, loader \\ &load/2)

Loads a value with the given type.

match?(schema_type, query_type)

Checks if a given type matches with a primitive type that can be found in queries.

primitive?(base)

Checks if we have a primitive type.

type(type)

Retrieves the underlying schema type for the given, possibly custom, type.

Callbacks

autogenerate()

Generates a loaded version of the data.

cast(term)

Casts the given input to the custom type.

dump(term)

Dumps the given term into an Ecto native type.

embed_as(format)

Dictates how the type should be treated inside embeds.

equal?(term, term)

Checks if two terms are semantically equal.

load(term)

Loads the given term into a custom type.

type()

Returns the underlying schema type for the custom type.

Types

base()

Specs

base() ::
  :integer
  | :float
  | :boolean
  | :string
  | :map
  | :binary
  | :decimal
  | :id
  | :binary_id
  | :utc_datetime
  | :naive_datetime
  | :date
  | :time
  | :any
  | :utc_datetime_usec
  | :naive_datetime_usec
  | :time_usec

composite()

Specs

composite() :: {:array, t()} | {:map, t()} | private_composite()

custom()

Specs

custom() :: module() | {:parameterized, module(), term()}

Custom types are represented by user-defined modules.

primitive()

Specs

primitive() :: base() | composite()

Primitive Ecto types (handled by Ecto).

t()

Specs

t() :: primitive() | custom()

An Ecto type, primitive or custom.

Functions

base?(atom)

Specs

base?(atom()) :: boolean()

Checks if the given atom can be used as base type.

iex> base?(:string)
true
iex> base?(:array)
false
iex> base?(Custom)
false

cast(type, value)

Specs

cast(t(), term()) :: {:ok, term()} | {:error, keyword()} | :error

Casts a value to the given type.

cast/2 is used by the finder queries and changesets to cast outside values to specific types.

Note that nil can be cast to all primitive types as data stores allow nil to be set on any column.

NaN and infinite decimals are not supported, use custom types instead.

iex> cast(:any, "whatever")
{:ok, "whatever"}

iex> cast(:any, nil)
{:ok, nil}
iex> cast(:string, nil)
{:ok, nil}

iex> cast(:integer, 1)
{:ok, 1}
iex> cast(:integer, "1")
{:ok, 1}
iex> cast(:integer, "1.0")
:error

iex> cast(:id, 1)
{:ok, 1}
iex> cast(:id, "1")
{:ok, 1}
iex> cast(:id, "1.0")
:error

iex> cast(:float, 1.0)
{:ok, 1.0}
iex> cast(:float, 1)
{:ok, 1.0}
iex> cast(:float, "1")
{:ok, 1.0}
iex> cast(:float, "1.0")
{:ok, 1.0}
iex> cast(:float, "1-foo")
:error

iex> cast(:boolean, true)
{:ok, true}
iex> cast(:boolean, false)
{:ok, false}
iex> cast(:boolean, "1")
{:ok, true}
iex> cast(:boolean, "0")
{:ok, false}
iex> cast(:boolean, "whatever")
:error

iex> cast(:string, "beef")
{:ok, "beef"}
iex> cast(:binary, "beef")
{:ok, "beef"}

iex> cast(:decimal, Decimal.new("1.0"))
{:ok, Decimal.new("1.0")}
iex> cast(:decimal, "1.0bad")
:error

iex> cast({:array, :integer}, [1, 2, 3])
{:ok, [1, 2, 3]}
iex> cast({:array, :integer}, ["1", "2", "3"])
{:ok, [1, 2, 3]}
iex> cast({:array, :string}, [1, 2, 3])
:error
iex> cast(:string, [1, 2, 3])
:error

composite?(atom)

Specs

composite?(atom()) :: boolean()

Checks if the given atom can be used as composite type.

iex> composite?(:array)
true
iex> composite?(:string)
false

dump(type, value, dumper \\ &dump/2)

Specs

dump(t(), term(), (t(), term() -> {:ok, term()} | :error)) ::
  {:ok, term()} | :error

Dumps a value to the given type.

Opposite to casting, dumping requires the returned value to be a valid Ecto type, as it will be sent to the underlying data store.

iex> dump(:string, nil)
{:ok, nil}
iex> dump(:string, "foo")
{:ok, "foo"}

iex> dump(:integer, 1)
{:ok, 1}
iex> dump(:integer, "10")
:error

iex> dump(:binary, "foo")
{:ok, "foo"}
iex> dump(:binary, 1)
:error

iex> dump({:array, :integer}, [1, 2, 3])
{:ok, [1, 2, 3]}
iex> dump({:array, :integer}, [1, "2", 3])
:error
iex> dump({:array, :binary}, ["1", "2", "3"])
{:ok, ["1", "2", "3"]}

embed_as(base, format)

Gets how the type is treated inside embeds for the given format.

See embed_as/1.

embedded_dump(type, value, format)

Dumps the value for type considering it will be embedded in format.

Examples

iex> Ecto.Type.embedded_dump(:decimal, Decimal.new("1"), :json)
{:ok, Decimal.new("1")}

embedded_load(type, value, format)

Loads the value for type considering it was embedded in format.

Examples

iex> Ecto.Type.embedded_load(:decimal, "1", :json)
{:ok, Decimal.new("1")}

equal?(type, term1, term2)

Specs

equal?(t(), term(), term()) :: boolean()

Checks if two terms are equal.

Depending on the given type performs a structural or semantical comparison.

Examples

iex> equal?(:integer, 1, 1)
true
iex> equal?(:decimal, Decimal.new("1"), Decimal.new("1.00"))
true

load(type, value, loader \\ &load/2)

Specs

load(t(), term(), (t(), term() -> {:ok, term()} | :error)) ::
  {:ok, term()} | :error

Loads a value with the given type.

iex> load(:string, nil)
{:ok, nil}
iex> load(:string, "foo")
{:ok, "foo"}

iex> load(:integer, 1)
{:ok, 1}
iex> load(:integer, "10")
:error

match?(schema_type, query_type)

Specs

match?(t(), primitive()) :: boolean()

Checks if a given type matches with a primitive type that can be found in queries.

iex> match?(:string, :any)
true
iex> match?(:any, :string)
true
iex> match?(:string, :string)
true

iex> match?({:array, :string}, {:array, :any})
true

iex> match?(Ecto.UUID, :uuid)
true
iex> match?(Ecto.UUID, :string)
false

primitive?(base)

Specs

primitive?(t()) :: boolean()

Checks if we have a primitive type.

iex> primitive?(:string)
true
iex> primitive?(Another)
false

iex> primitive?({:array, :string})
true
iex> primitive?({:array, Another})
true

type(type)

Specs

type(t()) :: t()

Retrieves the underlying schema type for the given, possibly custom, type.

iex> type(:string)
:string
iex> type(Ecto.UUID)
:uuid

iex> type({:array, :string})
{:array, :string}
iex> type({:array, Ecto.UUID})
{:array, :uuid}

iex> type({:map, Ecto.UUID})
{:map, :uuid}

Callbacks

autogenerate()

Specs

autogenerate() :: term()

Generates a loaded version of the data.

This is callback is invoked when a custom type is given to field with the :autogenerate flag.

cast(term)

Specs

cast(term()) :: {:ok, term()} | :error | {:error, keyword()}

Casts the given input to the custom type.

This callback is called on external input and can return any type, as long as the dump/1 function is able to convert the returned value into an Ecto native type. There are two situations where this callback is called:

  1. When casting values by Ecto.Changeset
  2. When passing arguments to Ecto.Query

You can return :error if the given term cannot be cast. A default error message of "is invalid" will be added to the changeset.

You may also return {:error, keyword()} to customize the changeset error message and its metadata. Passing a :message key, will override the default message. It is not possible to override the :type key.

For {:array, CustomType} or {:map, CustomType} the returned keyword list will be erased and the default error will be shown.

dump(term)

Specs

dump(term()) :: {:ok, term()} | :error

Dumps the given term into an Ecto native type.

This callback is called with any term that was stored in the struct and it needs to validate them and convert it to an Ecto native type.

embed_as(format)

Specs

embed_as(format :: atom()) :: :self | :dump

Dictates how the type should be treated inside embeds.

By default, the type is sent as itself, without calling dumping to keep the higher level representation. But it can be set to :dump so that it is dumped before being encoded.

equal?(term, term)

Specs

equal?(term(), term()) :: boolean()

Checks if two terms are semantically equal.

load(term)

Specs

load(term()) :: {:ok, term()} | :error

Loads the given term into a custom type.

This callback is called when loading data from the database and receives an Ecto native type. It can return any type, as long as the dump/1 function is able to convert the returned value back into an Ecto native type.

type()

Specs

type() :: t()

Returns the underlying schema type for the custom type.

For example, if you want to provide your own date structures, the type function should return :date.

Note this function is not required to return Ecto primitive types, the type is only required to be known by the adapter.

© 2013 Plataformatec
© 2020 Dashbit
Licensed under the Apache License, Version 2.0.
https://hexdocs.pm/ecto/Ecto.Type.html