WIP: Support field renaming

.rubocop.yml

@@ -4,3 +4,5 @@ inherit_gem:
 AllCops:
   TargetRubyVersion: 2.2
 
+Style/MultilineBlockChain:
+  Enabled: false

.ruby-version

@@ -0,0 +1 @@
+ruby-2.3.1

CHANGELOG.md

@@ -1,5 +1,9 @@
 # avromatic changelog
 
+## v0.8.0
+- Allow schema fields to be aliased if they conflict with an internal
+  method defined on the model.
+
 ## v0.7.1
 - Raise a more descriptive error when attempting to generate a model for a
   non-record Avro type.

README.md

@@ -148,6 +148,30 @@ inbound or outbound value is nil.
 If a custom type is registered for a record-type field, then any `to_avro` 
 method/Proc should return a Hash with string keys for encoding using Avro.
 
+#### Model Attribute Aliasing
+
+Note: this is different than the aliasing of fields and records within an Avro
+schema, which is not currently supported by the ruby `avro` gem.
+
+If a field in an Avro schema conflicts with the name of an internal method for a
+model, then field can be aliased by specifying the `aliases` option when
+defining the model.
+
+For example, `attributes` is a reserved name for Virtus (used internally by
+Avromatic). If a schema contains an attributes field, then it can be aliased
+to a different name on the model:
+
+```ruby
+Avromatic::Model.model(
+  schema_name: 'reserved_names',
+  aliases: { attributes: :my_attributes }
+)
+```
+
+A value for `attributes` will be assigned to `my_attributes` when creating an
+instance of the model, and the `my_attributes` value will be written to the
+`attributes` field when serializing to Avro.
+
 ### Encoding and Decoding
 
 `Avromatic` provides two different interfaces for encoding the key (optional)

lib/avromatic/model/attributes.rb

@@ -20,6 +20,8 @@ def self.first_union_schema(field_type)
 
       module ClassMethods
         def add_avro_fields
+          validate_schemas!
+
           if key_avro_schema
             check_for_field_conflicts!
             define_avro_attributes(key_avro_schema)
@@ -51,14 +53,11 @@ def schema_fields_differ?(name)
         end
 
         def define_avro_attributes(schema)
-          if schema.type_sym != :record
-            raise "Unsupported schema type '#{schema.type_sym}', only 'record' schemas are supported."
-          end
-
           schema.fields.each do |field|
-            field_class = avro_field_class(field.type)
+            field_class = avro_field_class(field: field)
+            field_name = avro_field_name(field.name)
 
-            attribute(field.name,
+            attribute(field_name,
                       field_class,
                       avro_field_options(field))
 
@@ -67,6 +66,40 @@ def define_avro_attributes(schema)
           end
         end
 
+        def validate_schemas!
+          [key_avro_schema, avro_schema].compact
+            .each { |schema| validate_schema!(schema) }
+        end
+
+        def validate_schema!(schema)
+          if schema.type_sym != :record
+            raise "Unsupported schema type '#{schema.type_sym}', only 'record' schemas are supported."
+          end
+
+          invalid_fields = schema.fields.select do |field|
+            instance_methods.include?(field.name.to_sym) && no_valid_alias?(field.name)
+          end
+          if invalid_fields.any?
+            raise "Disallowed field names: #{invalid_fields.map(&:name).map(&:inspect).join(', ')}.\n"\
+                  'Consider using the `aliases` option when defining the model to specify an alternate name.'
+          end
+        end
+
+        def raw_field_names
+          @raw_field_names ||=
+            [key_avro_schema, avro_schema].compact.flat_map(&:fields).map(&:name).to_set
+        end
+
+        # TODO: should this check for aliases that conflict with
+        # existing fields in general, or duplicate aliases?
+        # This is only checking the aliases for invalid fields.
+        def no_valid_alias?(name)
+          alias_name = aliases[name]
+          alias_name.nil? ||
+            (raw_field_names.include?(alias_name) &&
+             raise("alias `#{alias_name}` for field `#{name}` conflicts with an existing field."))
+        end
+
         def add_validation(field)
           case field.type.type_sym
           when :enum
@@ -96,7 +129,13 @@ def required?(field)
           !optional?(field)
         end
 
-        def avro_field_class(field_type)
+        def avro_field_name(field_name)
+          aliases[field_name] || field_name
+        end
+
+        def avro_field_class(field_type: nil, field: nil, name: nil)
+          field_type ||= field.type
+          field_name = name || field.name
           custom_type = Avromatic.type_registry.fetch(field_type)
           return custom_type.value_class if custom_type.value_class
 
@@ -114,24 +153,36 @@ def avro_field_class(field_type)
           when :null
             NilClass
           when :array
-            Array[avro_field_class(field_type.items)]
+            Array[avro_field_class(field_type: field_type.items, name: field_name)]
           when :map
-            Hash[String => avro_field_class(field_type.values)]
+            Hash[String => avro_field_class(field_type: field_type.values, name: field_name)]
           when :union
-            union_field_class(field_type)
+            union_field_class(field_type, field_name)
           when :record
             # TODO: This should add the generated model to a module.
             # A hash of generated models should be kept by name for reuse.
+            record_aliases = propagated_aliases(field_name)
             Class.new do
-              include Avromatic::Model.build(schema: field_type)
+              include Avromatic::Model.build(schema: field_type,
+                                             aliases: record_aliases)
             end
           else
             raise "Unsupported type #{field_type}"
           end
         end
 
-        def union_field_class(field_type)
-          avro_field_class(Avromatic::Model::Attributes.first_union_schema(field_type))
+        def propagated_aliases(prefix)
+          field_name_prefix = "#{prefix}."
+          aliases.select do |key, _value|
+            key.start_with?(field_name_prefix)
+          end.each_with_object(Hash.new) do |(key, value), result|
+            result[key.slice(field_name_prefix.length, key.length)] = value
+          end
+        end
+
+        def union_field_class(field_type, field_name)
+          avro_field_class(field_type: Avromatic::Model::Attributes.first_union_schema(field_type),
+                           name: field_name)
         end
 
         def avro_field_options(field)

lib/avromatic/model/configurable.rb

@@ -8,14 +8,19 @@ module Configurable
 
       module ClassMethods
         attr_accessor :config
-        delegate :avro_schema, :value_avro_schema, :key_avro_schema, to: :config
+        delegate :avro_schema, :value_avro_schema, :key_avro_schema,
+                 :aliases, :inverse_aliases, to: :config
+
+        def inherited(subclass)
+          subclass.config = config
+        end
 
         def value_avro_field_names
-          @value_avro_field_names ||= value_avro_schema.fields.map(&:name).map(&:to_sym).freeze
+          @value_avro_field_names ||= extract_field_names(value_avro_schema)
         end
 
         def key_avro_field_names
-          @key_avro_field_names ||= key_avro_schema.fields.map(&:name).map(&:to_sym).freeze
+          @key_avro_field_names ||= extract_field_names(key_avro_schema)
         end
 
         def value_avro_fields_by_name
@@ -26,8 +31,18 @@ def key_avro_fields_by_name
           @key_avro_fields_by_name ||= mapped_by_name(key_avro_schema)
         end
 
+        def inverse_aliases
+          @inverse_aliases ||= aliases.select { |k, _| k.index('.').nil? }.invert
+        end
+
         private
 
+        def extract_field_names(schema)
+          schema.fields.map do |field|
+            (aliases[field.name] || field.name).to_sym
+          end.freeze
+        end
+
         def mapped_by_name(schema)
           schema.fields.each_with_object(Hash.new) do |field, result|
             result[field.name.to_sym] = field
@@ -37,6 +52,7 @@ def mapped_by_name(schema)
 
       delegate :avro_schema, :value_avro_schema, :key_avro_schema,
                :value_avro_field_names, :key_avro_field_names,
+               :inverse_aliases,
                to: :class
     end
   end

lib/avromatic/model/configuration.rb

@@ -4,7 +4,7 @@ module Model
     # This class holds configuration for a model built from Avro schema(s).
     class Configuration
 
-      attr_reader :avro_schema, :key_avro_schema
+      attr_reader :avro_schema, :key_avro_schema, :aliases
       delegate :schema_store, to: Avromatic
 
       # Either schema(_name) or value_schema(_name), but not both, must be
@@ -21,6 +21,7 @@ def initialize(**options)
         @avro_schema = find_avro_schema(**options)
         raise ArgumentError.new('value_schema(_name) or schema(_name) must be specified') unless avro_schema
         @key_avro_schema = find_schema_by_option(:key_schema, **options)
+        @aliases = normalize_aliases(options[:aliases])
       end
 
       alias_method :value_avro_schema, :avro_schema
@@ -41,6 +42,12 @@ def find_schema_by_option(option_name, **options)
           (options[schema_name_option] && schema_store.find(options[schema_name_option]))
 
       end
+
+      def normalize_aliases(aliases)
+        (aliases || {}).each_with_object(Hash.new) do |(key, value), result|
+          result[key.to_s] = value.to_s
+        end.reject { |key, value| key == value }
+      end
     end
   end
 end

lib/avromatic/model/raw_serialization.rb

@@ -1,4 +1,5 @@
 require 'avromatic/model/passthrough_serializer'
+require 'active_support/core_ext/hash/indifferent_access'
 
 module Avromatic
   module Model
@@ -44,17 +45,19 @@ def hash_of_models?(key)
 
         def avro_hash(fields)
           attributes.slice(*fields).each_with_object(Hash.new) do |(key, value), result|
-            result[key.to_s] = if value.is_a?(Avromatic::Model::Attributes)
-                                 value.value_attributes_for_avro
-                               elsif array_of_models?(key)
-                                 value.map(&:value_attributes_for_avro)
-                               elsif hash_of_models?(key)
-                                 value.each_with_object({}) do |(k, v), hash|
-                                   hash[k] = v.value_attributes_for_avro
-                                 end
-                               else
-                                 avro_serializer[key].call(value)
-                               end
+            key_str = key.to_s
+            name = inverse_aliases[key_str] || key_str
+            result[name] = if value.is_a?(Avromatic::Model::Attributes)
+                             value.value_attributes_for_avro
+                           elsif array_of_models?(key)
+                             value.map(&:value_attributes_for_avro)
+                           elsif hash_of_models?(key)
+                             value.each_with_object({}) do |(k, v), hash|
+                               hash[k] = v.value_attributes_for_avro
+                             end
+                           else
+                             avro_serializer[key].call(value)
+                           end
           end
         end
 
@@ -80,8 +83,20 @@ def avro_raw_decode(key: nil, value:, key_schema: nil, value_schema: nil)
           new(value_attributes.merge!(key_attributes || {}))
         end
 
+        def new(attributes = {})
+          super(alias_attribute_hash(attributes))
+        end
+
         private
 
+        def alias_attribute_hash(model_attributes)
+          model_attributes.with_indifferent_access.tap do |hash|
+            (hash.keys & aliases.keys).each do |key|
+              hash[aliases[key]] = hash.delete(key)
+            end
+          end
+        end
+
         def decode_avro_datum(data, schema = nil, key_or_value = :value)
           stream = StringIO.new(data)
           decoder = Avro::IO::BinaryDecoder.new(stream)

lib/avromatic/version.rb

@@ -1,3 +1,3 @@
 module Avromatic
-  VERSION = '0.7.1'.freeze
+  VERSION = '0.8.0'.freeze
 end

spec/avro/dsl/test/reserved.rb

@@ -0,0 +1,10 @@
+namespace :test
+
+# record type contains fields that are either reserved words
+# for Virtus or methods that are used in the model implementation.
+record :reserved do
+  required :attributes, :array, items: :string
+  required :avro_message_value, :string
+  required :hash, :map, values: :string
+  required :okay, :string, default: ''
+end

spec/avro/schema/test/reserved.avsc

@@ -0,0 +1,30 @@
+{
+  "type": "record",
+  "name": "reserved",
+  "namespace": "test",
+  "fields": [
+    {
+      "name": "attributes",
+      "type": {
+        "type": "array",
+        "items": "string"
+      }
+    },
+    {
+      "name": "avro_message_value",
+      "type": "string"
+    },
+    {
+      "name": "hash",
+      "type": {
+        "type": "map",
+        "values": "string"
+      }
+    },
+    {
+      "name": "okay",
+      "type": "string",
+      "default": ""
+    }
+  ]
+}