Merge branch 'optionality-in-schemas'

README.md

@@ -142,6 +142,30 @@ conform!(%{user: %{name: "chris", age: -31}}, user_schema)
     (norm) lib/norm.ex:44: Norm.conform!/2
 ```
 
+Schema's are designed to allow systems to grow over time. They provide this
+functionality in two ways. The first is that any unspecified fields in the input
+are passed through when conforming the input. The second is that all keys in a
+schema are optional. This means that all of these are valid:
+
+```elixir
+user_schema = schema(%{
+  name: spec(is_binary()),
+  age: spec(is_integer()),
+})
+
+conform!(%{}, user_schema)
+=> %{}
+conform!(%{age: 31}, user_schema)
+=> %{age: 31}
+conform!(%{foo: :foo, bar: :bar}, user_schema)
+=> %{foo: :foo, bar: :bar}
+```
+
+If you're used to more restrictive systems for managing data these might seem
+like odd choices. We'll see how to specify required keys when we discuss Selections.
+
+#### Structs
+
 You can also create specs from structs:
 
 ```elixir
@@ -183,23 +207,12 @@ Schemas accomodate growth by disregarding any unspecified keys in the input map.
 This allows callers to start sending new data over time without coordination
 with the consuming function.
 
-### Selections
+### Selections and optionality
 
-You may have noticed that there's no way to specify optional keys in
-a schema. This may seem like an oversight but its actually an intentional
-design decision. Whether a key should be present in a schema is determined
-by the call site and not by the schema itself. For instance think about
-the assigns in a plug conn. When are the assigns optional? It depends on
-where you are in the pipeline.
-
-Schemas also force all keys to match at all times. This is generally
-useful as it limits your ability to introduce errors. But it also limits
-schema growth and turns changes that should be non-breaking into breaking
-changes.
-
-In order to support both of these scenarios Norm provides the
-`selection/2` function. `selection/2` allows you to specify exactly the
-keys you require from a schema at the place where you require them.
+We said that all of the fields in a schema are optional. In order to specify
+the keys that are required in a specific use case we can use a Selection. The
+Selections takes a schema and a list of keys - or keys to lists of keys - that
+must be present in the schema.
 
 ```elixir
 user_schema = schema(%{
@@ -211,13 +224,33 @@ user_schema = schema(%{
 just_age = selection(user_schema, [user: [:age]])
 
 conform!(%{user: %{name: "chris", age: 31}}, just_age)
-=> %{user: %{age: 31}}
+=> %{user: %{age: 31, name: "chris"}}
 
-# Selection also disregards unspecified keys
-conform!(%{user: %{name: "chris", age: 31, unspecified: nil}, other_stuff: :foo}, just_age)
-=> %{user: %{age: 31}}
+conform!(%{user: %{name: "chris"}}, just_age)
+** (Norm.MismatchError) Could not conform input:
+val: %{name: "chris"} in: :user/:age fails: :required
+    (norm) lib/norm.ex:387: Norm.conform!/2
 ```
 
+If you need to mark all fields in a schema as required you can elide the list
+of keys like so:
+
+```elixir
+user_schema = schema(%{
+  user: schema(%{
+    name: spec(is_binary()),
+    age: spec(is_integer()),
+  })
+})
+
+# Require all fields recursively
+conform!(%{user: %{name: "chris", age: 31}}, selection(user_schema))
+```
+
+Selections are an important tool because they give control over optionality
+back to the call site. This allows callers to determine what they actually need
+and makes schema's much more reusable.
+
 ### Patterns
 
 Norm provides a way to specify alternative specs using the `alt/1`
@@ -363,9 +396,7 @@ working to make improvements.
 Norm is being actively worked on. Any contributions are very welcome. Here is a
 limited set of ideas that are coming soon.
 
-- [ ] Support generators for other primitive types (floats, etc.)
 - [ ] More streamlined specification of keyword lists.
-- [ ] selections shouldn't need a path if you just want to match all the keys in the schema
 - [ ] Support "sets" of literal values
 - [ ] specs for functions and anonymous functions
 - [ ] easier way to do dispatch based on schema keys

lib/norm.ex

@@ -478,19 +478,64 @@ defmodule Norm do
   end
 
   @doc ~S"""
-  Creates a re-usable schema.
+  Creates a re-usable schema. Schema's are open which means that all keys are
+  optional and any non-specified keys are passed through without being conformed.
+  If you need to mark keys as required instead of optional you can use `selection`.
 
   ## Examples
 
-      iex> conform!(%{age: 31, name: "chris"},
-      ...>   schema(%{age: spec(is_integer()), name: spec(is_binary())})
-      ...> )
+      iex> valid?(%{}, schema(%{name: spec(is_binary())}))
+      true
+      iex> valid?(%{name: "Chris"}, schema(%{name: spec(is_binary())}))
+      true
+      iex> valid?(%{name: "Chris", age: 31}, schema(%{name: spec(is_binary())}))
+      true
+      iex> valid?(%{age: 31}, schema(%{name: spec(is_binary())}))
+      true
+      iex> valid?(%{name: 123}, schema(%{name: spec(is_binary())}))
+      false
+      iex> conform!(%{}, schema(%{name: spec(is_binary())}))
+      %{}
+      iex> conform!(%{age: 31, name: "chris"}, schema(%{name: spec(is_binary())}))
       %{age: 31, name: "chris"}
+      iex> conform!(%{age: 31}, schema(%{name: spec(is_binary())}))
+      %{age: 31}
+      iex> conform!(%{user: %{name: "chris"}}, schema(%{user: schema(%{name: spec(is_binary())})}))
+      %{user: %{name: "chris"}}
   """
   def schema(input) when is_map(input) do
     Schema.build(input)
   end
 
+  @doc ~S"""
+  Selections can be used to mark keys on a schema as required. Any unspecified keys
+  in the selection are still considered optional. Selections, like schemas,
+  are open and allow unspecied keys to be passed through. If no selectors are
+  provided then `selection` defaults to `:all` and recursively marks all keys in
+  all nested schema's. If the schema includes internal selections these selections
+  will not be overwritten.
+
+  ## Examples
+
+      iex> valid?(%{name: "chris"}, selection(schema(%{name: spec(is_binary())}), [:name]))
+      true
+      iex> valid?(%{}, selection(schema(%{name: spec(is_binary())}), [:name]))
+      false
+      iex> valid?(%{user: %{name: "chris"}}, selection(schema(%{user: schema(%{name: spec(is_binary())})}), [user: [:name]]))
+      true
+      iex> conform!(%{name: "chris"}, selection(schema(%{name: spec(is_binary())}), [:name]))
+      %{name: "chris"}
+      iex> conform!(%{name: "chris", age: 31}, selection(schema(%{name: spec(is_binary())}), [:name]))
+      %{name: "chris", age: 31}
+
+  ## Require all keys
+      iex> valid?(%{user: %{name: "chris"}}, selection(schema(%{user: schema(%{name: spec(is_binary())})})))
+      true
+  """
+  def selection(%Schema{} = schema, path \\ :all) do
+    Selection.new(schema, path)
+  end
+
   @doc ~S"""
   Chooses between alternative predicates or patterns. The patterns must be tagged with an atom.
   When conforming data to this specification the data is returned as a tuple with the tag.
@@ -527,19 +572,6 @@ defmodule Norm do
     Union.new(specs)
   end
 
-  @doc ~S"""
-  Selections provide a way to allow optional keys in a schema. This allows
-  schema's to be defined once and re-used in multiple scenarios.
-
-  ## Examples
-
-      iex> conform!(%{age: 31}, selection(schema(%{age: spec(is_integer()), name: spec(is_binary())}), [:age]))
-      %{age: 31}
-  """
-  def selection(%Schema{} = schema, path) do
-    Selection.new(schema, path)
-  end
-
   @doc ~S"""
   Specifies a generic collection. Collections can be any enumerable type.
 

lib/norm/schema.ex

@@ -4,7 +4,7 @@ defmodule Norm.Schema do
 
   alias __MODULE__
 
-  defstruct specs: [], struct: nil
+  defstruct specs: %{}, struct: nil
 
   # If we're building a schema from a struct then we need to add a default spec
   # for each key that only checks for presence. This allows users to specify
@@ -13,17 +13,12 @@ defmodule Norm.Schema do
     specs =
       struct
       |> Map.from_struct()
-      |> Enum.to_list()
 
     %Schema{specs: specs, struct: name}
   end
 
   def build(map) when is_map(map) do
-    specs =
-      map
-      |> Enum.to_list()
-
-    %Schema{specs: specs}
+    %Schema{specs: map}
   end
 
   def spec(schema, key) do
@@ -41,30 +36,34 @@ defmodule Norm.Schema do
       {:error, [Conformer.error(path, input, "not a map")]}
     end
 
+    # Conforming a struct
     def conform(%{specs: specs, struct: target}, input, path) when not is_nil(target) do
       # Ensure we're mapping the correct struct
-      if Map.get(input, :__struct__) == target do
-        with {:ok, conformed} <- check_specs(specs, input, path) do
-          {:ok, struct(target, conformed)}
-        end
-      else
-        short_name =
-          target
-          |> Atom.to_string()
-          |> String.replace("Elixir.", "")
+      cond do
+        Map.get(input, :__struct__) != target ->
+          short_name =
+            target
+            |> Atom.to_string()
+            |> String.replace("Elixir.", "")
+
+          {:error, [Conformer.error(path, input, "#{short_name}")]}
 
-        {:error, [Conformer.error(path, input, "#{short_name}")]}
+        true ->
+          with {:ok, conformed} <- check_specs(specs, Map.from_struct(input), path) do
+            {:ok, struct(target, conformed)}
+          end
       end
     end
 
+    # conforming a map.
     def conform(%Norm.Schema{specs: specs}, input, path) do
       check_specs(specs, input, path)
     end
 
     defp check_specs(specs, input, path) do
       results =
-        specs
-        |> Enum.map(&check_spec(&1, input, path))
+        input
+        |> Enum.map(&check_spec(&1, specs, path))
         |> Enum.reduce(%{ok: [], error: []}, fn {key, {result, conformed}}, acc ->
           Map.put(acc, result, acc[result] ++ [{key, conformed}])
         end)
@@ -80,24 +79,13 @@ defmodule Norm.Schema do
       end
     end
 
-    defp check_spec({key, nil}, input, path) do
-      case Map.has_key?(input, key) do
-        false ->
-          {key, {:error, [Conformer.error(path ++ [key], input, ":required")]}}
+    defp check_spec({key, value}, specs, path) do
+      case Map.get(specs, key) do
+        nil ->
+          {key, {:ok, value}}
 
-        true ->
-          {key, {:ok, Map.get(input, key)}}
-      end
-    end
-
-    defp check_spec({key, spec}, input, path) do
-      case Map.has_key?(input, key) do
-        false ->
-          {key, {:error, [Conformer.error(path ++ [key], input, ":required")]}}
-
-        true ->
-          val = Map.get(input, key)
-          {key, Conformable.conform(spec, val, path ++ [key])}
+        spec ->
+          {key, Conformable.conform(spec, value, path ++ [key])}
       end
     end
   end