Practical Ecto embedded schemas for data validation, coercion, and manipulation.
Practical Ecto
embedded_schema
s for data validation, coercion, and manipulation.
!
Variants of Ecto field
, embeds_one
, and embeds_many
macros to mark a field as required (see. Required Fields)Access
implementation to all schemasJason.Encoder
implementation to all schemasEcto.Schema
Reflection Functions
__schema__(:required)
- Returns list of fields marked as required (from !
macros)__schema__(:validations)
- Keyword
mapping of fields to validationschangeset
,new
,new!
,...) (see. Generated Functions)Application
-wide defaults for Ecto.Schema
API (see. Config)def deps do
[
{:flint, github: "acalejos/flint"}
]
end
Flint
is built on top of Ecto and is meant to provide good defaults for using embedded_schema
s for use outside of a database.
It also adds a bevy of convenient features to the existing Ecto
API to make writing schemas and validations much quicker.
Of course, since you're using Ecto, you can use this for use as an ORM, but this is emphasizing the use of embedded_schema
s as just more expressive and powerful maps while keeping compatibility with Ecto.Changeset
, Ecto.Type
, and all of the other benefits Ecto has to offer.
In particular, Flint
focuses on making it more ergonomic to use embedded_schema
s as a superset of Maps, so a Flint.Schema
by default implements the Access
behaviour and implements the Jason.Encoder
protocol.
Flint
also was made to leverage the distinction Ecto
makes between the embedded representation of the schema and the dumped representation. This means that you can dictate how you want the Elixir-side representation to look, and then provide transformations
for how it should be dumped, which helps when you want the serialized representation to look different.
This is useful if you want to make changes in the server-side code without needing to change the client-side (or vice-versa). Or perhaps you want a mapped representation, where instead of an Ecto.Enum
just converting its atom key to a string when dumped, it gets mapped to an integer, etc.
If you want to declare a schema with Flint
, just use Flint
within your module, and now you have access to Flint
's implementation of the
embedded_schema/1
macro. You can declare an embedded_schema
within your module as you otherwise would with Ecto
. Within the embedded_schema/1
block, you also have access to Flint
s implementations of embeds_one
,embeds_one!
,embeds_many
, embeds_many!
, field
, and field!
.
You can also use the shorthand notation, where you pass in your schema definition as an argument to the use/2
macro. Flint.__using__/1
also
accepts the following options which will be passed as module attributes to the Ecto
embedded_schema
. Refer to the Ecto.Schema
docs for more about these options.
primary_key
(default false
)schema_prefix
(default nil
)schema_context
(default nil
)timestamp_opts
(default [type: :naive_datetime]
)So these two are equivalent:
defmodule User do
use Flint
embedded_schema do
field! :username, :string
field! :password, :string, redacted: true
field :nickname, :string
end
end
is equivalent to:
defmodule User do
use Flint, schema: [
field!(:username, :string)
field!(:password, :string, redacted: true)
field(:nickname, :string)
]
end
If you're starting with Flint
and you know you will stick with it, the shorthand might make more sense. But if you want to be able to quickly
change between use Ecto.Schem
and use Flint
, or you're converting some existing Ecto
embedded_schema
s to Flint
, the latter might be
preferable.
Since a call to Flint
's embedded_schema
or use Flint, schema: []
just creates an Ecto
embedded_schema
you can use them just as you would any other Ecto
schemas. You can compose them, apply changesets to them, etc.
Flint
adds the convenience bang (!
) macros (embed_one!
,embed_many!
, field!
) for field declarations within your struct to declare a field as required within its changeset
function.
Flint
schemas also have a new reflection function in addition to the normal Ecto
reflection functions.
__schema__(:required)
-- Returns a list of all fields that were marked as required.Flint
allows you to colocate schema definitions and validations.
defmodule Person do
use Flint
embedded_schema do
field! :first_name, :string, max: 10, min: 5
field! :last_name, :string, min: 5, max: 10
field :favorite_colors, {:array, :string}, subset_of: ["red", "blue", "green"]
field! :age, :integer, greater_than: 0, less_than: 100
end
end
You can even parameterize the options passed to the validations:
defmodule Person do
use Flint
embedded_schema do
field! :first_name, :string, max: 10, min: 5
field! :last_name, :string, min: 5, max: 10
field :favorite_colors, {:array, :string}, subset_of: ["red", "blue", "green"]
field! :age, :integer, greater_than: 0, less_than: max_age
end
end
If you do this, make sure to pass the options as a keyword list into the call to changeset
:
Person.changeset(
%Person{},
%{first_name: "Bob", last_name: "Smith", favorite_colors: ["red", "blue", "pink"], age: 101},
[max_age: 100]
)
#Ecto.Changeset<
action: nil,
changes: %{
age: 101,
first_name: "Bob",
last_name: "Smith",
favorite_colors: ["red", "blue", "pink"]
},
errors: [
first_name: {"should be at least %{count} character(s)",
[count: 5, validation: :length, kind: :min, type: :string]},
favorite_colors: {"has an invalid entry", [validation: :subset, enum: ["red", "blue", "green"]]},
age: {"must be less than %{number}", [validation: :number, kind: :less_than, number: 100]}
],
data: #Person<>,
valid?: false,
...
>
This lets you change the parameters of the validations for each call to changeset
for more flexibility
Currently, the options / validations supported out of the box with Flint
are all based on validation functions
defined in Ecto.Changeset
:
:greater_than
(see. Ecto.Changeset.validate_number/3
):less_than
(see. Ecto.Changeset.validate_number/3
):less_than_or_equal_to
(see. Ecto.Changeset.validate_number/3
):greater_than_or_equal_to
(see. Ecto.Changeset.validate_number/3
):equal_to
(see. Ecto.Changeset.validate_number/3
):not_equal_to
(see. Ecto.Changeset.validate_number/3
):format
(see. Ecto.Changeset.validate_format/4
):subset_of
(see. Ecto.Changeset.validate_subset/4
):in
(see. Ecto.Changeset.validate_inlusion/4
):not_in
(see. Ecto.Changeset.validate_exclusion/4
):is
(see. Ecto.Changeset.validate_length/3
):min
(see. Ecto.Changeset.validate_length/3
):max
(see. Ecto.Changeset.validate_length/3
):count
(see. Ecto.Changeset.validate_length/3
)If you don't like the name of an option, you can provide a compile-time list of aliases to map new option names to existing options.
In your config, add an :aliases
key with a Keyword
value, where each key is the new alias, and the value is an existing option name.
For example, these are default aliases implemented in Flint
:
config Flint, aliases: [
lt: :less_than,
gt: :greater_than,
le: :less_than_or_equal_to,
ge: :greater_than_or_equal_to,
eq: :equal_to,
neq: :not_equal_to
]
NOTE If you add your own aliases and want to keep these above defaults, you will have to add them manually to your aliases.
__schema__(:validations)
Since validations are enforced through the generated changeset
functions, if you override this function you will not get the benefits
of the validations.
If you want to implement your own, you can use __schema__(:validations)
which is an added reflection function that stores validations.
NOTE These are stored as their quoted representation to support passing bindings, so make sure to account for this if implementing yourself.
If you want to override changeset
but want to keep the default validation behavior, there is also the Flint.Schema.validate_fields
function,
which accepts an %Ecto.Changetset{}
and optionally bindings, and performs validations using the information stored in __schema__(:validations)
.
Flint
provides default implementations for the following functions for any schema declaration. Each of these is overridable.
changeset
- Creates a changeset by casting all fields and validating all that were marked as required. If a :default
key is provided for a field, then any use of a bang (!
) declaration will essentially be ignored since the cast will fall back to the default before any valdiations are performed.new
- Creates a new changeset from the empty module struct and applies the changes (regardless of whether the changeset was valid).new!
- Same as new, except raises if the changeset is not valid.You can configure the default options set by Flint
.
embeds_one
: The default arguments when using embeds_one
. Defaults to [defaults_to_struct: true, on_replace: :delete]
embeds_one!
: The default arguments when using embeds_one!
. Defaults to [on_replace: :delete]
embeds_many
: The default arguments when using embeds_many
or embeds_many!
. Defaults to [on_replace: :delete]
embeds_many!
: The default arguments when using embeds_many!
. Defaults to [on_replace: :delete]
:enum
: The default arguments for an Ecto.Enum
field. Defaults to [embed_as: :dumped]
.:aliases
: See Aliases
You can also configure any aliases you want to use for schema validations.
Flint
takes advantage of the distinction Ecto
makes between an embedded_schema
's embedded and dumped representations.
For example, by default in Flint
, Ecto.Enum
s that are Keyword
(rather than just lists of atoms) will have their keys
be the embedded representation, and will have the values be the dumped representation.
defmodule Book do
use Flint, schema: [
field(:genre, Ecto.Enum, values: [biography: 0, science_fiction: 1, fantasy: 2, mystery: 3])
]
end
book = Book.new(%{genre: "biography"})
# %Book{genre: :biography}
Flint.Schema.dump(book)
# %{genre: 0}
In this example, you can see how you can share multiple representations of the same data using this distinction.
You can also implement your own Ecto.Type
and further customize this:
defmodule ContentType do
use Ecto.Type
def type, do: :atom
def cast("application/json"), do: {:ok, :json}
def cast(_), do: :error
def load(_), do: :error
def dump(:json), do: {:ok, "application/json"}
def dump(_), do: :error
def embed_as(_) do
:dump
end
end
Here, cast
will be called when creating a new Flint
schema from a map, and dump
will be used
when calling Flint.Schema.dump/1
.
defmodule URL do
use Flint, schema: [
field(:content_type, ContentType)
]
end
url = URL.new(%{content_type: "application/json"})
# %URL{content_type: :json}
Flint.Schema.dump(url)
# %{content_type: "application/json"}
You can view the Notebooks folder for some examples in LIivebook.
You can also look at Merquery for a real, comprehensive
example of how to use Flint
.