class Sequel::Postgres::Dataset

Constants

BindArgumentMethods
PREPARED_ARG_PLACEHOLDER: :nocov:
PreparedStatementMethods

Public Instance Methods

Source

    # File lib/sequel/adapters/postgres.rb
739 def bound_variable_modules
740   [BindArgumentMethods]
741 end

fetch_rows (sql) { |h| ... }

Source

    # File lib/sequel/adapters/postgres.rb
650 def fetch_rows(sql)
651   return cursor_fetch_rows(sql){|h| yield h} if @opts[:cursor]
652   execute(sql){|res| yield_hash_rows(res, fetch_rows_set_cols(res)){|h| yield h}}
653 end

paged_each (opts=OPTS) { || ... }

Source

    # File lib/sequel/adapters/postgres.rb
656 def paged_each(opts=OPTS, &block)
657   unless defined?(yield)
658     return enum_for(:paged_each, opts)
659   end
660   use_cursor(opts).each(&block)
661 end

Use a cursor for paging.

prepared_arg_placeholder ()

Source

    # File lib/sequel/adapters/postgres.rb
749 def prepared_arg_placeholder
750   PREPARED_ARG_PLACEHOLDER
751 end

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

prepared_statement_modules ()

Source

    # File lib/sequel/adapters/postgres.rb
743 def prepared_statement_modules
744   [PreparedStatementMethods]
745 end

use_cursor (opts=OPTS)

Source

    # File lib/sequel/adapters/postgres.rb
686 def use_cursor(opts=OPTS)
687   clone(:cursor=>{:rows_per_fetch=>1000}.merge!(opts))
688 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.
:skip_transaction: Same as :hold, but :hold takes priority.

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.

where_current_of (cursor_name='sequel_cursor')

Source

    # File lib/sequel/adapters/postgres.rb
698 def where_current_of(cursor_name='sequel_cursor')
699   clone(:where=>Sequel.lit(['CURRENT OF '], Sequel.identifier(cursor_name)))
700 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

Private Instance Methods

call_procedure (name, args)

Source

    # File lib/sequel/adapters/postgres.rb
757 def call_procedure(name, args)
758   sql = String.new
759   sql << "CALL "
760   identifier_append(sql, name)
761   sql << "("
762   expression_list_append(sql, args)
763   sql << ")"
764   with_sql_first(sql)
765 end

Generate and execute a procedure call.

cursor_fetch_rows (sql) { |h| ... }

Source

    # File lib/sequel/adapters/postgres.rb
768 def cursor_fetch_rows(sql)
769   cursor = @opts[:cursor]
770   hold = cursor.fetch(:hold){cursor[:skip_transaction]}
771   server_opts = {:server=>@opts[:server] || :read_only, :skip_transaction=>hold}
772   cursor_name = quote_identifier(cursor[:cursor_name] || 'sequel_cursor')
773   rows_per_fetch = cursor[:rows_per_fetch].to_i
774 
775   db.transaction(server_opts) do 
776     begin
777       execute_ddl("DECLARE #{cursor_name} NO SCROLL CURSOR WITH#{'OUT' unless hold} HOLD FOR #{sql}", server_opts)
778       rows_per_fetch = 1000 if rows_per_fetch <= 0
779       fetch_sql = "FETCH FORWARD #{rows_per_fetch} FROM #{cursor_name}"
780       cols = nil
781       # Load columns only in the first fetch, so subsequent fetches are faster
782       execute(fetch_sql) do |res|
783         cols = fetch_rows_set_cols(res)
784         yield_hash_rows(res, cols){|h| yield h}
785         return if res.ntuples < rows_per_fetch
786       end
787       while true
788         execute(fetch_sql) do |res|
789           yield_hash_rows(res, cols){|h| yield h}
790           return if res.ntuples < rows_per_fetch
791         end
792       end
793     rescue Exception => e
794       raise
795     ensure
796       begin
797         execute_ddl("CLOSE #{cursor_name}", server_opts)
798       rescue
799         raise e if e
800         raise
801       end
802     end
803   end
804 end

Use a cursor to fetch groups of records at a time, yielding them to the block.

fetch_rows_set_cols (res)

Source

    # File lib/sequel/adapters/postgres.rb
808 def fetch_rows_set_cols(res)
809   cols = []
810   procs = db.conversion_procs
811   res.nfields.times do |fieldnum|
812     cols << [procs[res.ftype(fieldnum)], output_identifier(res.fname(fieldnum))]
813   end
814   self.columns = cols.map{|c| c[1]}
815   cols
816 end

Set the columns based on the result set, and return the array of field numers, type conversion procs, and name symbol arrays.

literal_blob_append (sql, v)

Source

    # File lib/sequel/adapters/postgres.rb
819 def literal_blob_append(sql, v)
820   sql << "'" << db.synchronize(@opts[:server]){|c| c.escape_bytea(v)} << "'"
821 end

Use the driver’s escape_bytea

literal_string_append (sql, v)

Source

    # File lib/sequel/adapters/postgres.rb
824 def literal_string_append(sql, v)
825   sql << "'" << db.synchronize(@opts[:server]){|c| c.escape_string(v)} << "'"
826 end

Use the driver’s escape_string

yield_hash_rows (res, cols) { |converted_rec| ... }

Source

    # File lib/sequel/adapters/postgres.rb
830 def yield_hash_rows(res, cols)
831   ntuples = res.ntuples
832   recnum = 0
833   while recnum < ntuples
834     fieldnum = 0
835     nfields = cols.length
836     converted_rec = {}
837     while fieldnum < nfields
838       type_proc, fieldsym = cols[fieldnum]
839       value = res.getvalue(recnum, fieldnum)
840       converted_rec[fieldsym] = (value && type_proc) ? type_proc.call(value) : value
841       fieldnum += 1 
842     end
843     yield converted_rec
844     recnum += 1
845   end
846 end

For each row in the result set, yield a hash with column name symbol keys and typecasted values.