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.
DatasetClass | = | self |
APOS | = | Sequel::Dataset::APOS |
DEFAULT_CURSOR_NAME | = | 'sequel_cursor'.freeze |
PREPARED_ARG_PLACEHOLDER | = | LiteralString.new('$').freeze |
BindArgumentMethods | = | prepared_statements_module(:bind, [ArgumentMapper, ::Sequel::Postgres::DatasetMethods::PreparedStatementMethods], %w'execute execute_dui') |
PreparedStatementMethods | = | prepared_statements_module(:prepare, BindArgumentMethods, %w'execute execute_dui') do # Raise a more obvious error if you attempt to call a unnamed prepared statement. def call(*) |
Yield all rows returned by executing the given SQL and converting the types.
# File lib/sequel/adapters/postgres.rb, line 675 675: def fetch_rows(sql) 676: return cursor_fetch_rows(sql){|h| yield h} if @opts[:cursor] 677: execute(sql){|res| yield_hash_rows(res, fetch_rows_set_cols(res)){|h| yield h}} 678: end
Use a cursor for paging.
# File lib/sequel/adapters/postgres.rb, line 681 681: def paged_each(opts=OPTS, &block) 682: use_cursor(opts).each(&block) 683: 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:
: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 707 707: def use_cursor(opts=OPTS) 708: clone(:cursor=>{:rows_per_fetch=>1000}.merge!(opts)) 709: 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 719 719: def where_current_of(cursor_name=DEFAULT_CURSOR_NAME) 720: clone(:where=>Sequel.lit(['CURRENT OF '], Sequel.identifier(cursor_name))) 721: end