class Sequel::Postgres::Dataset

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

Constants

APOS
BindArgumentMethods
DEFAULT_CURSOR_NAME
DatasetClass
PREPARED_ARG_PLACEHOLDER
PreparedStatementMethods

Public Instance Methods

bound_variable_modules() click to toggle source
# File lib/sequel/adapters/postgres.rb, line 780
def bound_variable_modules
  [BindArgumentMethods]
end
fetch_rows(sql) { |h| ... } click to toggle source

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

# File lib/sequel/adapters/postgres.rb, line 691
def fetch_rows(sql)
  return cursor_fetch_rows(sql){|h| yield h} if @opts[:cursor]
  execute(sql){|res| yield_hash_rows(res, fetch_rows_set_cols(res)){|h| yield h}}
end
paged_each(opts=OPTS, &block) click to toggle source

Use a cursor for paging.

# File lib/sequel/adapters/postgres.rb, line 697
def paged_each(opts=OPTS, &block)
  use_cursor(opts).each(&block)
end
prepared_arg_placeholder() click to toggle source

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

# File lib/sequel/adapters/postgres.rb, line 790
def prepared_arg_placeholder
  PREPARED_ARG_PLACEHOLDER
end
prepared_statement_modules() click to toggle source
# File lib/sequel/adapters/postgres.rb, line 784
def prepared_statement_modules
  [PreparedStatementMethods]
end
use_cursor(opts=OPTS) click to toggle source

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.

# File lib/sequel/adapters/postgres.rb, line 723
def use_cursor(opts=OPTS)
  clone(:cursor=>{:rows_per_fetch=>1000}.merge!(opts))
end
where_current_of(cursor_name='sequel_cursor') click to toggle source

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
# File lib/sequel/adapters/postgres.rb, line 735
def where_current_of(cursor_name='sequel_cursor')
  clone(:where=>Sequel.lit(['CURRENT OF '], Sequel.identifier(cursor_name)))
end