feat(orm): add Prism and Orm

lib/prism/orm/habtm_collection.rb

@@ -0,0 +1,73 @@
+module Prism
+  module Orm
+    # Many-to-many collection proxy for has_and_belongs_to_many, backed by a
+    # plain join table (id, left_key, right_key) with no model of its own.
+    class HabtmCollection
+      include Enumerable
+      include CollectionSerialization
+
+      def initialize(owner, target:, join_table:, left_key:, right_key:)
+        @owner = owner
+        @target = target
+        @join_table = join_table
+        @left_key = left_key
+        @right_key = right_key
+      end
+
+      def to_a
+        ids = target_ids
+        ids.empty? ? [] : @target.where(id: ids).to_a
+      end
+
+      def each
+        return enum_for(:each) unless block_given?
+        to_a.each { |record| yield record }
+      end
+
+      def ids
+        target_ids
+      end
+
+      def count
+        target_ids.size
+      end
+
+      def include?(record)
+        target_ids.include?(record.id)
+      end
+
+      def <<(record)
+        return self if include?(record)
+        store.insert(@join_table, @left_key => @owner.id, @right_key => record.id)
+        self
+      end
+      alias_method :push, :<<
+
+      def delete(record)
+        row = join_rows.find { |r| r[@right_key] == record.id }
+        store.delete(@join_table, row['id']) if row
+        self
+      end
+
+      def replace(records)
+        join_rows.each { |row| store.delete(@join_table, row['id']) }
+        records.each { |record| self << record }
+        self
+      end
+
+      private
+
+      def store
+        @owner.class.store
+      end
+
+      def join_rows
+        store.all(@join_table).select { |row| row[@left_key] == @owner.id }
+      end
+
+      def target_ids
+        join_rows.map { |row| row[@right_key] }
+      end
+    end
+  end
+end