Ecto v2.2.8 Ecto.Type behaviour View Source

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

A custom type expects 4 functions to be implemented, all documented and described below. We also provide two examples of how custom types can be used in Ecto to augment existing types or providing your own types.

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
  @behaviour 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, we are guaranteed to
  # receive a map (as databases are strict) and we will
  # 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

Link to this section 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

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

cast(term)

Casts the given input to the custom type

dump(term)

Dumps the given term into an Ecto native type

load(term)

Loads the given term into a custom type

type()

Returns the underlying schema type for the custom type

Link to this section Types

custom()

custom() :: atom()

Custom types are represented by user-defined modules.

primitive()

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

Primitive Ecto types (handled by Ecto).

t()

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

An Ecto type, primitive or custom.

Link to this section Functions

base?(atom)

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)

cast(t(), term()) :: {:ok, term()} | :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.

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, Decimal.new("1.0"))
{:ok, Decimal.new(1.0)}

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)

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)

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"]}

A dumper function may be given for handling recursive types.

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

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

A loader function may be given for handling recursive types.

match?(schema_type, query_type)

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)

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)

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}

Link to this section Callbacks

cast(term)

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

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:

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

dump(term)

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.

load(term)

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

Loads the given term into a custom type.

This callback is called when loading data from the database and receive 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()

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.