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

Dataset class for PostgreSQL datasets that use the pg, postgres, or postgres-pr driver.

Methods

call   fetch_rows   prepare   prepared_arg_placeholder   use_cursor  

Included Modules

Sequel::Postgres::DatasetMethods

Classes and Modules

Module Sequel::Postgres::Dataset::ArgumentMapper
Module Sequel::Postgres::Dataset::BindArgumentMethods
Module Sequel::Postgres::Dataset::PreparedStatementMethods

Constants

DatasetClass = self
APOS = Sequel::Dataset::APOS
PREPARED_ARG_PLACEHOLDER = LiteralString.new('$').freeze

Public Instance methods

call(type, bind_vars={}, *values, &block)

Execute the given type of statement with the hash of values.

[Source]

     # File lib/sequel/adapters/postgres.rb, line 708
708:         def call(type, bind_vars={}, *values, &block)
709:           ps = to_prepared_statement(type, values)
710:           ps.extend(BindArgumentMethods)
711:           ps.call(bind_vars, &block)
712:         end
fetch_rows(sql) {|h| ...}

Yield all rows returned by executing the given SQL and converting the types.

[Source]

     # File lib/sequel/adapters/postgres.rb, line 596
596:       def fetch_rows(sql)
597:         return cursor_fetch_rows(sql){|h| yield h} if @opts[:cursor]
598:         execute(sql){|res| yield_hash_rows(res, fetch_rows_set_cols(res)){|h| yield h}}
599:       end
prepare(type, name=nil, *values)

Prepare the given type of statement with the given name, and store it in the database to be called later.

[Source]

     # File lib/sequel/adapters/postgres.rb, line 716
716:         def prepare(type, name=nil, *values)
717:           ps = to_prepared_statement(type, values)
718:           ps.extend(PreparedStatementMethods)
719:           if name
720:             ps.prepared_statement_name = name
721:             db.set_prepared_statement(name, ps)
722:           end
723:           ps
724:         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 730
730:         def prepared_arg_placeholder
731:           PREPARED_ARG_PLACEHOLDER
732:         end
use_cursor(opts={})

Uses a cursor for fetching records, instead of fetching the entire result set at once. Can be used to process large datasets without holding all rows in memory (which is what the underlying drivers do by default). Options:

  • :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}

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

[Source]

     # File lib/sequel/adapters/postgres.rb, line 616
616:       def use_cursor(opts={})
617:         clone(:cursor=>{:rows_per_fetch=>1000}.merge(opts))
618:       end

[Validate]