class OccamsRecord::Merge

Represents a merge operation to be performed. Merges are always “left” merges. You initialize the Merge with the “left” records, and the name of the attribute into which “right” records will be placed.

After initializing, perform a specific type of merge by calling the appropriate *! method.

Attributes

target_rows[R]

@return [Array<OccamsRecord::Results::Row>] the rows into which associated rows will be merged

Public Class Methods

new(target_rows, assoc_attr) click to toggle source

Initialize a new Merge operation.

@param target_rows [Array<OccamsRecord::Results::Row] the rows into which associated rows should be merged @param assoc_attr [String|Symbol] name of the attribute where associated rows will be put

# File lib/occams-record/merge.rb, line 18
def initialize(target_rows, assoc_attr)
  @target_rows = target_rows
  @assign = "#{assoc_attr}="
end

Public Instance Methods

many!(assoc_rows, mapping) click to toggle source

Merge an array of assoc_rows into the target_rows. Some target_rows may end up with 0 matching associations, and they'll be assigned empty arrays.

@param assoc_rows [Array<OccamsRecord::Results::Row>] rows to merge into target_rows @param mapping [Hash] The fields that should match up. The keys are for the target rows and the values for the associated rows.

# File lib/occams-record/merge.rb, line 90
def many!(assoc_rows, mapping)
  target_attrs = mapping.keys
  assoc_attrs = mapping.values

  # Optimized for merges where there's a single mapping key pair (which is the vast majority)
  if mapping.size == 1
    target_attr, assoc_attr = target_attrs[0], assoc_attrs[0]
    begin
      assoc_rows_by_attr = assoc_rows.group_by { |r|
        r.send assoc_attr
      }
    rescue NoMethodError => e
      raise MissingColumnError.new(assoc_rows[0], e.name)
    end

    target_rows.each do |row|
      begin
        pkey = row.send target_attr
      rescue NoMethodError => e
        raise MissingColumnError.new(row, e.name)
      end
      row.send(@assign, assoc_rows_by_attr[pkey] || [])
    end

  # Slower but works with any number of mapping key pairs
  else
    begin
      assoc_rows_by_attrs = assoc_rows.group_by { |r|
        assoc_attrs.map { |attr| r.send attr }
      }
    rescue NoMethodError => e
      raise MissingColumnError.new(assoc_rows[0], e.name)
    end

    target_rows.each do |row|
      begin
        pkeys = target_attrs.map { |attr| row.send attr }
      rescue NoMethodError => e
        raise MissingColumnError.new(row, e.name)
      end
      row.send(@assign, assoc_rows_by_attrs[pkeys] || [])
    end
  end

  nil
end
single!(assoc_rows, mapping) click to toggle source

Merge a single assoc_row into each target_rows (or nil if one can't be found). target_attr and assoc_attr are the matching keys on target_rows and assoc_rows, respectively.

@param assoc_rows [Array<OccamsRecord::Results::Row>] rows to merge into target_rows @param mapping [Hash] The fields that should match up. The keys are for the target rows and the values for the associated rows.

# File lib/occams-record/merge.rb, line 31
def single!(assoc_rows, mapping)
  target_attrs = mapping.keys
  assoc_attrs = mapping.values

  # Optimized for merges where there's a single mapping key pair (which is the vast majority)
  if mapping.size == 1
    target_attr, assoc_attr = target_attrs[0], assoc_attrs[0]
    assoc_rows_by_ids = assoc_rows.reduce({}) { |a, assoc_row|
      begin
        id = assoc_row.send assoc_attr
      rescue NoMethodError => e
        raise MissingColumnError.new(assoc_row, e.name)
      end
      a[id] ||= assoc_row
      a
    }

    target_rows.each do |row|
      begin
        attr = row.send target_attr
      rescue NoMethodError => e
        raise MissingColumnError.new(row, e.name)
      end
      row.send(@assign, attr ? assoc_rows_by_ids[attr] : nil)
    end

  # Slower but works with any number of mapping key pairs
  else
    assoc_rows_by_ids = assoc_rows.reduce({}) { |a, assoc_row|
      begin
        ids = assoc_attrs.map { |attr| assoc_row.send attr }
      rescue NoMethodError => e
        raise MissingColumnError.new(assoc_row, e.name)
      end
      a[ids] ||= assoc_row
      a
    }

    target_rows.each do |row|
      begin
        attrs = target_attrs.map { |attr| row.send attr }
      rescue NoMethodError => e
        raise MissingColumnError.new(row, e.name)
      end
      row.send(@assign, attrs.any? ? assoc_rows_by_ids[attrs] : nil)
    end
  end

  nil
end