You are an expert in writing code in many different languages. Your goal is to perform code completion for the following code, keeping in mind the rest of the code and the file meta data.
    Metadata details:
    filename: model_injector.rb
    path of file: ./repos/pg_party/lib/pg_party
    
    the code of the file until where you have to start completion: # frozen_string_literal: true

module PgParty
  class ModelInjector
    def initialize(model, *key, &blk)
      @model = model
      @key = key.flatten.compact
      @key_blk = blk
    end

    def inject_range_methods
      require "pg_party/model/range_methods"

      inject_methods_for(PgParty::Model::RangeMethods)
    end

    def in
    
    def create_class_attributes
      @model.class_attribute(
        :partition_key,
        :complex_partition_key,
        instance_accessor: false,
        instance_predicate: false
      )

      if @key_blk
        @model.partition_key = @key_blk.call
        @model.complex_partition_key = true
      else
        if @key.size == 1
          @model.partition_key = @key.first
        else
          @model.partition_key = @key
        end