Dataset class for PostgreSQL datasets that use the pg, postgres, or postgres-pr driver.
# File lib/sequel/adapters/postgres.rb, line 780 def bound_variable_modules [BindArgumentMethods] end
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
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
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
# File lib/sequel/adapters/postgres.rb, line 784 def prepared_statement_modules [PreparedStatementMethods] end
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:
The name assigned to the cursor (default ‘sequel_cursor’). Nested cursors require different names.
Declare the cursor WITH HOLD and don’t use transaction around the cursor usage.
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
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