edit json encoding protocol of schemas to allow default=nil if explic…

…itly requested

lib/avrogen/avro/types.ex

@@ -2,5 +2,5 @@ alias Avrogen.Avro.Types
 import Avrogen.Utils.MacroUtils
 
 jason_decode_skip_null_impl(Types.Record)
-jason_decode_skip_null_impl(Types.Record.Field)
+jason_decode_skip_null_field_impl(Types.Record.Field)
 jason_decode_skip_null_impl(Types.Enum)

lib/avrogen/avro/types/record/field.ex

@@ -10,6 +10,8 @@ defmodule Avrogen.Avro.Types.Record.Field do
 
   @type order :: :ascending | :descending | :ignore
 
+  @explicitly_null_default "explicitly_null_default"
+
   typedstruct do
     # A JSON string providing the name of the enum (required).
     field :name, String.t(), enforce: true
@@ -40,11 +42,20 @@ defmodule Avrogen.Avro.Types.Record.Field do
   end
 
   def parse(%{"name" => name, "type" => type} = field) do
+    # We must be able to differentiate between default=nil and default not set.
+    default =
+      case Map.fetch(field, "default") do
+        :error -> nil
+        {:ok, "null"} -> @explicitly_null_default
+        {:ok, nil} -> @explicitly_null_default
+        {:ok, other} -> other
+      end
+
     %__MODULE__{
       name: name,
       doc: field["doc"],
       type: Schema.parse(type),
-      default: parse_default_value(field["default"]),
+      default: default,
       order: field["order"],
       aliases: field["aliases"],
       pii: field["pii"] || false,
@@ -57,11 +68,6 @@ defmodule Avrogen.Avro.Types.Record.Field do
   def comment(%__MODULE__{doc: nil, name: name}), do: "#{name}: #{name}"
   def comment(%__MODULE__{doc: doc, name: name}), do: "#{name}: #{doc}"
 
-  # The only way to differentiate between "default is nil because there isn't one" and "default is actually null" is to
-  # check if the type is also a union with null.
-  def has_default?(%__MODULE__{default: nil, type: %Types.Union{} = union}),
-    do: Types.Union.optional_by_convention?(union)
-
   def has_default?(%__MODULE__{default: nil}), do: false
   def has_default?(%__MODULE__{}), do: true
 
@@ -82,15 +88,16 @@ defmodule Avrogen.Avro.Types.Record.Field do
     variable_name = Code.string_to_quoted!(name)
 
     case default do
-      default when is_nil(default) or default == "null" ->
+      default when default == @explicitly_null_default ->
         quote(do: unquote(variable_name) = avro_map[unquote(name)])
 
       default ->
         quote(do: unquote(variable_name) = avro_map[unquote(name)] || unquote(default))
     end
   end
 
-  def typed_struct_field(%__MODULE__{name: name, type: type, default: nil} = field) do
+  def typed_struct_field(%__MODULE__{name: name, type: type, default: default} = field)
+      when default == @explicitly_null_default do
     name = String.to_atom(name)
 
     quote do
@@ -109,10 +116,6 @@ defmodule Avrogen.Avro.Types.Record.Field do
     end
   end
 
-  def parse_default_value(nil), do: nil
-  def parse_default_value("null"), do: nil
-  def parse_default_value(value), do: value
-
   def enforce?(%__MODULE__{type: %Types.Union{} = union}),
     do: not Types.Union.has_member?(union, Types.Primitive.null())
 

lib/avrogen/avro/types/union.ex

@@ -15,7 +15,6 @@ defmodule Avrogen.Avro.Types.Union do
   """
 
   alias Avrogen.Avro.Schema
-  alias Avrogen.Avro.Types.Primitive
   use TypedStruct
 
   typedstruct do
@@ -26,10 +25,6 @@ defmodule Avrogen.Avro.Types.Union do
   def parse(value) when is_list(value), do: %__MODULE__{types: Enum.map(value, &Schema.parse/1)}
 
   def has_member?(%__MODULE__{types: types}, type), do: Enum.member?(types, type)
-
-  # A union with null listed first is optional by convention (see moduledoc).
-  def optional_by_convention?(%__MODULE__{types: [first_type | _]}),
-    do: first_type == Primitive.null()
 end
 
 alias Avrogen.Avro.Schema.CodeGenerator

lib/avrogen/util/macro.ex

@@ -27,4 +27,27 @@ defmodule Avrogen.Utils.MacroUtils do
       end
     end
   end
+
+  defmacro jason_decode_skip_null_field_impl(type) do
+    quote do
+      defimpl Jason.Encoder, for: unquote(type) do
+        def encode(%unquote(type){} = value, opts) do
+          value
+          |> Map.from_struct()
+          |> Map.reject(fn {_k, v} -> is_nil(v) end)
+          |> then(fn map ->
+            # TODO get from config?
+            case Map.get(map, :default) do
+              "explicitly_null_default" ->
+                Map.put(map, :default, nil)
+
+              _other ->
+                map
+            end
+          end)
+          |> Jason.Encode.map(opts)
+        end
+      end
+    end
+  end
 end