Module: ArJdbc::Util::TableCopier

Included in:
Derby
Defined in:
lib/arjdbc/util/table_copier.rb

Instance Method Summary collapse

Instance Method Details

#alter_table(table_name, options = {}) ⇒ Object

Performs changes for table by first copying (and preserving contents) into another (temporary) table, than alters and copies all data back.



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# File 'lib/arjdbc/util/table_copier.rb', line 11

def alter_table(table_name, options = {})
  table_name = table_name.to_s.downcase
  altered_table_name = "a#{table_name}"
  caller = lambda { |definition| yield definition if block_given? }

  transaction do
    # A temporary table might improve performance here, but
    # it doesn't seem to maintain indices across the whole move.
    move_table(table_name, altered_table_name, options)
    move_table(altered_table_name, table_name, &caller)
  end
end

#copy_table(from, to, options = {}) ⇒ Object

See Also:



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# File 'lib/arjdbc/util/table_copier.rb', line 33

def copy_table(from, to, options = {})
  from_primary_key = primary_key(from)
  create_table(to, options.merge(:id => false)) do |definition|
    @definition = definition
    @definition.primary_key(from_primary_key) if from_primary_key.present?
    columns(from).each do |column|
      column_name = options[:rename] ?
        (options[:rename][column.name] ||
         options[:rename][column.name.to_sym] ||
         column.name) : column.name

      next if column_name == from_primary_key

      @definition.column(column_name, column.type,
        :limit => column.limit, :default => column.default,
        :precision => column.precision, :scale => column.scale,
        :null => column.null)
    end
    yield @definition if block_given?
  end

  copy_table_indexes(from, to, options[:rename] || {})
  copy_table_contents(from, to,
    @definition.columns.map {|column| column.name},
    options[:rename] || {})
end

#copy_table_contents(from, to, columns, rename = {}) ⇒ Object

Copies the content of a table into another.



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# File 'lib/arjdbc/util/table_copier.rb', line 84

def copy_table_contents(from, to, columns, rename = {})
  column_mappings = Hash[ columns.map { |name| [name, name] } ]
  rename.each { |a| column_mappings[a.last] = a.first }
  from_columns = columns(from).collect {|col| col.name}
  columns = columns.find_all{ |col| from_columns.include?(column_mappings[col]) }
  quoted_columns = columns.map { |col| quote_column_name(col) } * ','

  quoted_to = quote_table_name(to)

  raw_column_mappings = Hash[ columns(from).map { |c| [c.name, c] } ]

  execute("SELECT * FROM #{quote_table_name(from)}", 'Copy Table').each do |row|
    sql = "INSERT INTO #{quoted_to} (#{quoted_columns}) VALUES ("

    column_values = columns.map do |col|
      quote(row[column_mappings[col]], raw_column_mappings[col])
    end

    sql << column_values * ', '
    sql << ')'
    exec_insert sql, 'Copy Table', []
  end
end

#copy_table_indexes(from, to, rename = {}) ⇒ Object

Copies indexes for a given table.



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# File 'lib/arjdbc/util/table_copier.rb', line 61

def copy_table_indexes(from, to, rename = {})
  indexes(from).each do |index|
    name = index.name.downcase
    if to == "a#{from}"
      name = "t#{name}"
    elsif from == "a#{to}"
      name = name[1..-1]
    end

    to_column_names = columns(to).map(&:name)
    columns = index.columns.map { |column| rename[column] || column }
    columns = columns.select { |column| to_column_names.include?(column) }

    unless columns.empty?
      # index name can't be the same
      opts = { :name => name.gsub(/(^|_)(#{from})_/, "\\1#{to}_"), :internal => true }
      opts[:unique] = true if index.unique
      add_index(to, columns, opts)
    end
  end
end

#move_table(from, to, options = {}, &block) ⇒ Object

Move a table into another while preserving all content.

See Also:



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# File 'lib/arjdbc/util/table_copier.rb', line 26

def move_table(from, to, options = {}, &block)
  copy_table(from, to, options, &block)
  drop_table(from)
end