diff --git a/lib/prism/orm/nested_attributes.rb b/lib/prism/orm/nested_attributes.rb
new file mode 100644
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--- /dev/null
+++ b/lib/prism/orm/nested_attributes.rb
@@ -0,0 +1,184 @@
+module Prism
+  module Orm
+    # accepts_nested_attributes_for :comments - lets a parent form submit its
+    # own attributes plus a nested collection (or single record, for has_one)
+    # of child attributes in one request, e.g. `post.update(title: 'x',
+    # comments_attributes: [{ body: 'hi' }, { id: 3, _destroy: '1' }])`,
+    # mirroring ActiveRecord's autosave associations.
+    #
+    # Building, validating and persisting happen in two callbacks registered
+    # on the *first* accepts_nested_attributes_for call for a given name:
+    # `before_save` builds every child record, runs its own `valid?`, and
+    # copies any failures onto the parent's own `errors` under the
+    # association name, aborting the whole save (via `throw :abort`, same as
+    # every other before_* hook in this ORM) before anything is written.
+    # Only once that has passed does `after_save` set each child's foreign
+    # key to the now-guaranteed-present parent id and save (or destroy) it -
+    # this has to be `after_save`, not `before_save`, because a brand-new
+    # parent has no id to hand its children until the insert has happened,
+    # and both hooks run inside the same `transaction` block as the parent's
+    # own write (see Model#save), so an exception anywhere in the chain
+    # unwinds the parent's insert/update too instead of leaving orphans.
+    module NestedAttributes
+      class TooManyRecords < StandardError; end
+
+      def self.included(base)
+        base.extend(ClassMethods)
+      end
+
+      module ClassMethods
+        def nested_attributes_options
+          @nested_attributes_options ||= {}
+        end
+
+        def accepts_nested_attributes_for(name, allow_destroy: false, reject_if: nil, limit: nil)
+          name = name.to_sym
+          meta = associations[name]
+          raise ArgumentError, "no association #{name.inspect} to accept nested attributes for" unless meta
+          unless %i[has_many has_one].include?(meta[:type])
+            raise ArgumentError,
+                  "accepts_nested_attributes_for only supports has_many/has_one (#{name.inspect} is #{meta[:type].inspect})"
+          end
+
+          nested_attributes_options[name] = {
+            allow_destroy: allow_destroy, reject_if: reject_if, limit: limit, collection: meta[:type] == :has_many
+          }
+
+          define_method("#{name}_attributes=") do |attributes|
+            (@nested_attributes_pending ||= {})[name] = attributes
+          end
+
+          register_nested_attributes_callbacks(name)
+        end
+
+        private
+
+        def nested_attributes_registered
+          @nested_attributes_registered ||= []
+        end
+
+        def register_nested_attributes_callbacks(name)
+          return if nested_attributes_registered.include?(name)
+          nested_attributes_registered << name
+
+          before_save { process_nested_attributes_before_save(name) }
+          after_save { process_nested_attributes_after_save(name) }
+        end
+      end
+
+      private
+
+      def process_nested_attributes_before_save(name)
+        pending = @nested_attributes_pending&.delete(name)
+        return unless pending
+
+        options = self.class.nested_attributes_options[name]
+        meta = self.class.associations[name]
+        built = build_nested_records(name, pending, options, meta)
+        (@nested_attributes_built ||= {})[name] = built
+        throw :abort if built.any? { |entry| entry[:invalid] }
+      end
+
+      def process_nested_attributes_after_save(name)
+        built = @nested_attributes_built&.delete(name)
+        return unless built
+
+        meta = self.class.associations[name]
+        built.each do |entry|
+          record = entry[:record]
+          if entry[:destroy]
+            record.destroy if record.persisted?
+          else
+            record[meta[:foreign_key]] = id
+            record[meta[:type_key]] = self.class.name if meta[:type_key]
+            record.save
+          end
+        end
+      end
+
+      def build_nested_records(name, pending, options, meta)
+        target_class = Object.const_get(meta[:class_name])
+        entries = options[:collection] ? normalize_nested_collection(pending) : [pending]
+
+        if options[:limit] && entries.size > options[:limit]
+          raise NestedAttributes::TooManyRecords, "maximum #{options[:limit]} records are allowed for #{name}"
+        end
+
+        entries.each_with_object([]) do |raw_attrs, list|
+          entry = build_one_nested_record(name, raw_attrs, options, meta, target_class)
+          list << entry if entry
+        end
+      end
+
+      def build_one_nested_record(name, raw_attrs, options, meta, target_class)
+        attrs = stringify_nested_keys(raw_attrs)
+        id_value = attrs.delete('id')
+        destroy_flag = nested_truthy?(attrs.delete('_destroy'))
+
+        if id_value.nil? || id_value == ''
+          return nil if reject_nested_record?(options[:reject_if], attrs)
+          record = target_class.new
+        else
+          record = find_existing_nested_record(target_class, meta, id_value)
+          if record.nil?
+            errors.add(name, "references an invalid or inaccessible #{Inflector.underscore(meta[:class_name])}")
+            return { record: nil, destroy: false, invalid: true }
+          end
+        end
+
+        return { record: record, destroy: true, invalid: false } if destroy_flag && options[:allow_destroy]
+
+        record.assign(attrs)
+        if record.valid?
+          { record: record, destroy: false, invalid: false }
+        else
+          record.errors.full_messages.each { |message| errors.add(name, message) }
+          { record: record, destroy: false, invalid: true }
+        end
+      end
+
+      # Looks the child up by primary key (Store#find coerces the id, unlike
+      # a plain `where`/`find_by` scan - HTTP params always arrive as
+      # strings, so a raw `find_by(id: "3")` against an Integer-keyed row
+      # would silently miss every time) and only then checks it actually
+      # belongs to this parent, so an id copied from a different parent's
+      # child is rejected rather than quietly hijacked.
+      def find_existing_nested_record(target_class, meta, id_value)
+        return nil if new_record?
+        record = target_class.find(id_value)
+        return nil unless record[meta[:foreign_key]] == id
+        return nil if meta[:type_key] && record[meta[:type_key]] != self.class.name
+        record
+      rescue RecordNotFound
+        nil
+      end
+
+      def normalize_nested_collection(pending)
+        case pending
+        when Hash then pending.values
+        when Array then pending
+        else raise ArgumentError, "expected a Hash or Array of attribute hashes, got #{pending.class}"
+        end
+      end
+
+      def stringify_nested_keys(attrs)
+        attrs.each_with_object({}) { |(key, value), out| out[key.to_s] = value }
+      end
+
+      def nested_truthy?(value)
+        [true, 'true', '1', 1].include?(value)
+      end
+
+      def reject_nested_record?(reject_if, attrs)
+        case reject_if
+        when nil then false
+        when :all_blank
+          attrs.values.all? { |value| value.nil? || (value.respond_to?(:empty?) && value.empty?) }
+        when Symbol then send(reject_if, attrs)
+        when Proc then reject_if.call(attrs)
+        else false
+        end
+      end
+    end
+  end
+end