method

merge_target_lists

v3.2.13 - Show latest stable - 0 notes - Class: CollectionAssociation

merge_target_lists(persisted, memory) private

We have some records loaded from the database (persisted) and some that are in-memory (memory). The same record may be represented in the persisted array and in the memory array.

So the task of this method is to merge them according to the following rules:

* The final array must not have duplicates
* The order of the persisted array is to be preserved
* Any changes made to attributes on objects in the memory array are to be preserved
* Otherwise, attributes should have the value found in the database

Show source

# File activerecord/lib/active_record/associations/collection_association.rb, line 400
        def merge_target_lists(persisted, memory)
          return persisted if memory.empty?
          return memory    if persisted.empty?

          persisted.map! do |record|
            # Unfortunately we cannot simply do memory.delete(record) since on 1.8 this returns
            # record rather than memory.at(memory.index(record)). The behavior is fixed in 1.9.
            mem_index = memory.index(record)

            if mem_index
              mem_record = memory.delete_at(mem_index)

              ((record.attribute_names & mem_record.attribute_names) - mem_record.changes.keys).each do |name|
                mem_record[name] = record[name]
              end

              mem_record
            else
              record
            end
          end

          persisted + memory
        end

merge_target_lists

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