Contents

module ArJdbc
  module PostgreSQL
    module ExplainSupport
      def supports_explain?
        true
      end

      def explain(arel, binds = [])
        sql = "EXPLAIN #{to_sql(arel, binds)}"
        result = exec_query(sql, "EXPLAIN", binds)
        ExplainPrettyPrinter.new.pp result # we can assume AR >= 3.1
      end

      class ExplainPrettyPrinter # :nodoc:
        # Pretty prints the result of a 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)
        #
        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
      end
    end
  end
end

Version data entries

12 entries across 12 versions & 1 rubygems

Version	Path
activerecord-jdbc-adapter-1.3.8	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.7	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.6	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.5	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.4	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.3	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.2	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.1	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.0	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.0.rc1	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.0.beta2	lib/arjdbc/postgresql/explain_support.rb
activerecord-jdbc-adapter-1.3.0.beta1	lib/arjdbc/postgresql/explain_support.rb