class ActiveRecord::SchemaMigration

:nodoc:
to be executed the next time.
number is inserted in to the schema migrations table so it doesn’t need
have been applied to a given database. When a migration is run, its schema
This class is used to create a table that keeps track of which migrations

def count 

def count
  sm = Arel::SelectManager.new(arel_table)
  sm.project(*Arel::Nodes::Count.new([Arel.star]))
  @pool.with_connection do |connection|
    connection.select_values(sm, "#{self.class} Count").first
  end
end

def create_table 

def create_table
  @pool.with_connection do |connection|
    unless connection.table_exists?(table_name)
      connection.create_table(table_name, id: false) do |t|
        t.string :version, **connection.internal_string_options_for_primary_key
      end
    end
  end
end

def create_version(version) 

def create_version(version)
  im = Arel::InsertManager.new(arel_table)
  im.insert(arel_table[primary_key] => version)
  @pool.with_connection do |connection|
    connection.insert(im, "#{self.class} Create", primary_key, version)
  end
end

def delete_all_versions 

def delete_all_versions
  # Eagerly check in connection to avoid checking in/out many times in the called method.
  @pool.with_connection do
    versions.each do |version|
      delete_version(version)
    end
  end
end

def delete_version(version) 

def delete_version(version)
  dm = Arel::DeleteManager.new(arel_table)
  dm.wheres = [arel_table[primary_key].eq(version)]
  @pool.with_connection do |connection|
    connection.delete(dm, "#{self.class} Destroy")
  end
end

def drop_table 

def drop_table
  @pool.with_connection do |connection|
    connection.drop_table table_name, if_exists: true
  end
end

def initialize(pool) 

def initialize(pool)
  @pool = pool
  @arel_table = Arel::Table.new(table_name)
end

def integer_versions 

def integer_versions
  versions.map(&:to_i)
end

def normalize_migration_number(number) 

def normalize_migration_number(number)
  "%.3d" % number.to_i
end

def normalized_versions 

def normalized_versions
  versions.map { |v| normalize_migration_number v }
end

def primary_key 

def primary_key
  "version"
end

def table_exists? 

def table_exists?
  @pool.with_connection do |connection|
    connection.data_source_exists?(table_name)
  end
end

def table_name 

def table_name
  "#{ActiveRecord::Base.table_name_prefix}#{ActiveRecord::Base.schema_migrations_table_name}#{ActiveRecord::Base.table_name_suffix}"
end

def versions 

def versions
  sm = Arel::SelectManager.new(arel_table)
  sm.project(arel_table[primary_key])
  sm.order(arel_table[primary_key].asc)
  @pool.with_connection do |connection|
    connection.select_values(sm, "#{self.class} Load")
  end
end