Add support for relation.infer_id_from_class setting

lib/rom/runtime.rb

@@ -136,7 +136,15 @@ def auto_register(directory, **options)
     # @api private
     def register_constant(type, constant)
       if config.key?(constant.config.component.type)
-        constant.config.component.join!(config[constant.config.component.type])
+        parent_config = config[constant.config.component.type]
+        const_config = constant.config.component
+
+        const_config.inherit!(parent_config).join!(parent_config)
+
+        # TODO: make this work with all components
+        if const_config.key?(:infer_id_from_class) && const_config.infer_id_from_class
+          const_config.id = const_config.inflector.component_id(constant.name)&.to_sym
+        end
       end
 
       components.add(type, constant: constant, config: constant.config.component)

lib/rom/settings.rb

@@ -62,6 +62,7 @@ module ROM
     setting :type, default: :relation
     setting :abstract
     setting :id
+    setting :infer_id_from_class, inherit: true
     setting :namespace, default: "relations"
     setting :dataset
     setting :adapter

spec/suite/rom/runtime/register_relation_spec.rb

@@ -0,0 +1,31 @@
+# frozen_string_literal: true
+
+require "rom/runtime"
+
+RSpec.describe ROM::Runtime, "#register_relation" do
+  subject(:runtime) do
+    ROM::Runtime.new
+  end
+
+  let(:resolver) do
+    runtime.resolver
+  end
+
+  it "registers a relation class using provided component's id" do
+    stub_const("Users", Class.new(ROM::Relation) { config.component.id = :users })
+
+    runtime.register_relation(Users)
+
+    expect(resolver["relations.users"]).to be_instance_of(Users)
+  end
+
+  it "registers a relation class with component's id inferred from the class name" do
+    runtime.config.relation.infer_id_from_class = true
+
+    stub_const("Users", Class.new(ROM::Relation))
+
+    runtime.register_relation(Users)
+
+    expect(resolver["relations.users"]).to be_instance_of(Users)
+  end
+end