Class: ActiveRecord::ConnectionAdapters::PostgreSQL::ExplainPrettyPrinter

Inherits:
Object
  • Object
show all
Defined in:
lib/active_record/connection_adapters/postgresql/explain_pretty_printer.rb

Overview

:nodoc:

Instance Method Summary collapse

Instance Method Details

#pp(result) ⇒ Object

Pretty prints the result of an EXPLAIN in a way that resembles the output of the PostgreSQL shell:

                                  QUERY PLAN
------------------------------------------------------------------------------
 Nested Loop Left Join  (cost=0.00..37.24 rows=8 width=0)
   Join Filter: (posts.user_id = users.id)
   ->  Index Scan using users_pkey on users  (cost=0.00..8.27 rows=1 width=4)
         Index Cond: (id = 1)
   ->  Seq Scan on posts  (cost=0.00..28.88 rows=8 width=4)
         Filter: (posts.user_id = 1)
(6 rows)



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# File 'lib/active_record/connection_adapters/postgresql/explain_pretty_printer.rb', line 18

def pp(result)
  header = result.columns.first
  lines  = result.rows.map(&:first)

  # We add 2 because there's one char of padding at both sides, note
  # the extra hyphens in the example above.
  width = [header, *lines].map(&:length).max + 2

  pp = []

  pp << header.center(width).rstrip
  pp << "-" * width

  pp += lines.map { |line| " #{line}" }

  nrows = result.rows.length
  rows_label = nrows == 1 ? "row" : "rows"
  pp << "(#{nrows} #{rows_label})"

  pp.join("\n") + "\n"
end