From 8fd23c52deb96772f73593cdb72e2f7c34c54f8b Mon Sep 17 00:00:00 2001
From: =?UTF-8?q?Marc=20Busqu=C3=A9?= <marc@lamarciana.com>
Date: Wed, 2 Jan 2019 16:28:51 +0100
Subject: [PATCH] Map canonical names and aliases in a schema

---
 core/lib/rom/schema.rb            | 11 +++++++++++
 core/spec/unit/rom/schema_spec.rb |  9 +++++++++
 2 files changed, 20 insertions(+)

diff --git a/core/lib/rom/schema.rb b/core/lib/rom/schema.rb
index 65605bc2a..b888e8ba6 100644
--- a/core/lib/rom/schema.rb
+++ b/core/lib/rom/schema.rb
@@ -430,6 +430,17 @@ def to_ast
       [:schema, [name, attributes.map(&:to_ast)]]
     end
 
+    # Hash from canonical name to alias for aliased attributes
+    #
+    # @return [Hash<Symbol, Symbol>]
+    #
+    # @api public
+    def alias_mapping
+      each_with_object({}) do |attr, obj|
+        obj[attr.name] = attr.alias if attr.aliased?
+      end
+    end
+
     # @api private
     def set!(key, value)
       instance_variable_set("@#{ key }", value)
diff --git a/core/spec/unit/rom/schema_spec.rb b/core/spec/unit/rom/schema_spec.rb
index e94f03bf2..c6caf2666 100644
--- a/core/spec/unit/rom/schema_spec.rb
+++ b/core/spec/unit/rom/schema_spec.rb
@@ -54,4 +54,13 @@
       expect(schema.project(:name).primary_key_name).to be(:id)
     end
   end
+
+  describe '#alias_mapping' do
+    it 'returns a hash from canonical name to alias including aliased attributes' do
+      attrs = { id: ROM::Types::Integer.meta(name: :id, alias: :pk), name: ROM::Types::String }
+      schema = ROM::Schema.define(:name, attributes: attrs.values)
+
+      expect(schema.alias_mapping).to eq(id: :pk)
+    end
+  end
 end