Class Sequel::Postgres::Dataset
In: lib/sequel/adapters/postgres.rb
Parent: Sequel::Dataset

Methods

bound_variable_modules   fetch_rows   paged_each   prepared_arg_placeholder   prepared_statement_modules   use_cursor   where_current_of  

Included Modules

Sequel::Postgres::DatasetMethods

Classes and Modules

Module Sequel::Postgres::Dataset::ArgumentMapper

Constants

PREPARED_ARG_PLACEHOLDER = LiteralString.new('$').freeze
BindArgumentMethods = prepared_statements_module(:bind, [ArgumentMapper], %w'execute execute_dui')
PreparedStatementMethods = prepared_statements_module(:prepare, BindArgumentMethods, %w'execute execute_dui')

Public Instance methods

bound_variable_modules()

[Source]

     # File lib/sequel/adapters/postgres.rb, line 678
678:         def bound_variable_modules
679:           [BindArgumentMethods]
680:         end
fetch_rows(sql) {|h| ...}

[Source]

     # File lib/sequel/adapters/postgres.rb, line 590
590:       def fetch_rows(sql)
591:         return cursor_fetch_rows(sql){|h| yield h} if @opts[:cursor]
592:         execute(sql){|res| yield_hash_rows(res, fetch_rows_set_cols(res)){|h| yield h}}
593:       end
paged_each(opts=OPTS, &block)

Use a cursor for paging.

[Source]

     # File lib/sequel/adapters/postgres.rb, line 596
596:       def paged_each(opts=OPTS, &block)
597:         use_cursor(opts).each(&block)
598:       end
prepared_arg_placeholder()

PostgreSQL uses $N for placeholders instead of ?, so use a $ as the placeholder.

[Source]

     # File lib/sequel/adapters/postgres.rb, line 688
688:         def prepared_arg_placeholder
689:           PREPARED_ARG_PLACEHOLDER
690:         end
prepared_statement_modules()

[Source]

     # File lib/sequel/adapters/postgres.rb, line 682
682:         def prepared_statement_modules
683:           [PreparedStatementMethods]
684:         end
use_cursor(opts=OPTS)

Uses a cursor for fetching records, instead of fetching the entire result set at once. Note this uses a transaction around the cursor usage by default and can be changed using `hold: true` as described below. Cursors can be used to process large datasets without holding all rows in memory (which is what the underlying drivers may do by default). Options:

:cursor_name :The name assigned to the cursor (default ‘sequel_cursor’). Nested cursors require different names.
:hold :Declare the cursor WITH HOLD and don‘t use transaction around the cursor usage.
:rows_per_fetch :The number of rows per fetch (default 1000). Higher numbers result in fewer queries but greater memory use.

Usage: 

  DB[:huge_table].use_cursor.each{|row| p row}
  DB[:huge_table].use_cursor(rows_per_fetch: 10000).each{|row| p row}
  DB[:huge_table].use_cursor(cursor_name: 'my_cursor').each{|row| p row}

This is untested with the prepared statement/bound variable support, and unlikely to work with either.

[Source]

     # File lib/sequel/adapters/postgres.rb, line 622
622:       def use_cursor(opts=OPTS)
623:         clone(:cursor=>{:rows_per_fetch=>1000}.merge!(opts))
624:       end
where_current_of(cursor_name='sequel_cursor')

Replace the WHERE clause with one that uses CURRENT OF with the given cursor name (or the default cursor name). This allows you to update a large dataset by updating individual rows while processing the dataset via a cursor: 

  DB[:huge_table].use_cursor(rows_per_fetch: 1).each do |row|
    DB[:huge_table].where_current_of.update(column: ruby_method(row))
  end

[Source]

     # File lib/sequel/adapters/postgres.rb, line 634
634:       def where_current_of(cursor_name='sequel_cursor')
635:         clone(:where=>Sequel.lit(['CURRENT OF '], Sequel.identifier(cursor_name)))
636:       end

[Validate]