Class: OccamsRecord::Merge

Inherits:
Object
  • Object
show all
Defined in:
lib/occams-record/merge.rb

Overview

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.

Instance Attribute Summary collapse

Instance Method Summary collapse

Constructor Details

#initialize(target_rows, assoc_attr) ⇒ Merge

Initialize a new Merge operation.



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# File 'lib/occams-record/merge.rb', line 18

def initialize(target_rows, assoc_attr)
  @target_rows = target_rows
  @assign = "#{assoc_attr}="
end

Instance Attribute Details

#target_rows ⇒ Array<OccamsRecord::Results::Row> (readonly) 



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# File 'lib/occams-record/merge.rb', line 10

def target_rows
  @target_rows
end

Instance Method Details

#many!(assoc_rows, mapping) ⇒ Object

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.

for the associated rows.



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# 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) ⇒ Object

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.

for the associated rows.



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# 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