Checking types
For checking input in Exchema
you call the validation function
is?/2
. It receives the input and the type for running checks.
iex> Exchema.is?("1234", Exchema.Types.String)
true
iex> Exchema.is?(1234, Exchema.Types.String)
false
iex> Exchema.is?(1234, Exchema.Types.Integer)
true
Types
Now that checking is out of the way. Let’s extend to what is a type.
It can be:
- the global type
:any
- a type reference such as
Exchema.Types.String
- a type refinement such as
{:ref, :any, length: 1}
(more about this in predicates guide) - a type application (for parametric types) such as
{Exchema.Types.List, Exchema.Types.String}
Errors
When checking returns false, we can see what caused that with the
errors/2
function:
iex> Exchema.errors(1234, Exchema.Types.String)
[{{Exchema.Predicates, :is}, :binary, :not_a_binary}]
This is also helpful when you have several errors. Let’s check that:
# import the DSL
import Exchema.Notation
# alias the types
alias Exchema.Types, as: T
# define a User structure
structure User, first_name: T.String, last_name: T.String
# Type this on iex
iex> Exchema.errors(%User{first_name: 123, last_name: 123}, User)
[
{{Exchema.Predicates, :fields},
[first_name: Exchema.Types.String, last_name: Exchema.Types.String],
{:nested_errors,
[
first_name: [{{Exchema.Predicates, :is}, :binary, :not_a_binary}],
last_name: [{{Exchema.Predicates, :is}, :binary, :not_a_binary}]
]}}
]
Flatten errors
We can also flatten the errors for better reading:
iex> errors = Exchema.errors(%User{first_name: 123, last_name: 123}, User)
# output omitted
iex> Exchema.flatten_errors(errors)
[
{[:first_name], {Exchema.Predicates, :is}, :binary, :not_a_binary},
{[:last_name], {Exchema.Predicates, :is}, :binary, :not_a_binary}
]
This is very useful for debugging errors.
Nested types
You can nest types without issues and check nested errors. Example:
import Exchema.Notation
# Name here has no predicate other than its super type. You might want
# to add predicates later like checking if its upcased.
subtype Name, Exchema.Types.String, []
# This is a different type of predicate than 'is'.
subtype Country, Exchema.Types.Atom, [inclusion: ~w{brazil canada portugal}a]
# This extends from `:any` because list and maps descend from any
subtype Metadata, :any, &(is_list(&1) || is_map(&1))
structure FullName, [first: Name, last: Name]
defmodule MyStructure do
structure [
name: FullName, # nested model
country: Country,
metadata: Metadata # generic data
]
end
valid = %MyStructure{
name: %FullName{
first: "Bernardo",
last: "Amorim"
},
country: :brazil,
metadata: %{any: :thing}
}
invalid = %MyStructure{
name: %FullName{
first: 1234,
last: :not_a_string
},
country: :croatia,
metadata: :not_a_list_nor_a_map
}
Exchema.is?(valid, MyStructure)
# => true
Exchema.is?(invalid, MyStructure)
# => false
Exchema.errors(invalid, MyStructure)
# => [{{Exchema.Predicates, :map},[fields: [...]],{:nested_errors, ...]
invalid |> Exchema.errors(MyStructure) |> Exchema.Error.flattened
# => [
# {[:name, :first], {Exchema.Predicates, :is}, :binary, :not_a_binary},
# {[:name, :last], {Exchema.Predicates, :is}, :binary, :not_a_binary},
# {[:country], {Exchema.Predicates, :inclusion}, [:brazil, :canada, :portugal],
# :invalid},
# {[:metadata], {Exchema.Predicates, :fun},
# #Function<0.33830354/1 in :elixir_compiler_0.__MODULE__/1>, :invalid}
# ]