Class: Sequel::Postgres::Dataset

Inherits:
Dataset show all
Includes:
DatasetMethods
Defined in:
lib/sequel/adapters/postgres.rb

Defined Under Namespace

Modules: ArgumentMapper

Constant Summary

PREPARED_ARG_PLACEHOLDER =
LiteralString.new('$').freeze
BindArgumentMethods =
prepared_statements_module(:bind, [ArgumentMapper], %w'execute execute_dui')
PreparedStatementMethods =
prepared_statements_module(:prepare, BindArgumentMethods, %w'execute execute_dui')

Constants included from DatasetMethods

Sequel::Postgres::DatasetMethods::LOCK_MODES, Sequel::Postgres::DatasetMethods::NULL

Constants inherited from Dataset

Dataset::ACTION_METHODS, Dataset::BITWISE_METHOD_MAP, Dataset::COLUMNS_CLONE_OPTIONS, Dataset::COLUMN_CHANGE_OPTS, Dataset::CONDITIONED_JOIN_TYPES, Dataset::COUNT_FROM_SELF_OPTS, Dataset::COUNT_OF_ALL_AS_COUNT, Dataset::COUNT_SELECT, Dataset::DEFAULT, Dataset::DEFAULT_PREPARED_STATEMENT_MODULE_METHODS, Dataset::EMPTY_ARRAY, Dataset::EMPTY_SELECT, Dataset::EXISTS, Dataset::EXTENSIONS, Dataset::IS_LITERALS, Dataset::IS_OPERATORS, Dataset::JOIN_METHODS, Dataset::LIKE_OPERATORS, Dataset::NON_SQL_OPTIONS, Dataset::N_ARITY_OPERATORS, Dataset::OPTS, Dataset::PREPARED_STATEMENT_MODULE_CODE, Dataset::QUALIFY_KEYS, Dataset::QUERY_METHODS, Dataset::REGEXP_OPERATORS, Dataset::TRUE_FREEZE, Dataset::TWO_ARITY_OPERATORS, Dataset::UNCONDITIONED_JOIN_TYPES, Dataset::WILDCARD

Instance Attribute Summary

Attributes inherited from Dataset

#db, #opts

Instance Method Summary collapse

Methods included from DatasetMethods

#analyze, #complex_expression_sql_append, #disable_insert_returning, #explain, #for_share, #full_text_search, #insert, #insert_conflict, #insert_ignore, #insert_select, #insert_select_sql, #lock, #supports_cte?, #supports_cte_in_subqueries?, #supports_distinct_on?, #supports_group_cube?, #supports_group_rollup?, #supports_grouping_sets?, #supports_insert_conflict?, #supports_insert_select?, #supports_lateral_subqueries?, #supports_modifying_joins?, #supports_regexp?, #supports_returning?, #supports_skip_locked?, #supports_timestamp_timezones?, #supports_window_functions?, #truncate, #window

Methods inherited from Dataset

#<<, #==, #[], #add_graph_aliases, #aliased_expression_sql_append, #all, #array_sql_append, #as_hash, #avg, #bind, #boolean_constant_sql_append, #call, #case_expression_sql_append, #cast_sql_append, clause_methods, #clone, #column_all_sql_append, #columns, #columns!, #complex_expression_sql_append, #constant_sql_append, #count, #current_datetime, def_sql_method, #delayed_evaluation_sql_append, #delete, #distinct, #dup, #each, #each_server, #empty?, #eql?, #escape_like, #except, #exclude, #exclude_having, #exists, #extension, #filter, #first, #first!, #first_source, #first_source_alias, #first_source_table, #for_update, #freeze, #from, #from_self, #frozen?, #function_sql_append, #get, #graph, #grep, #group, #group_and_count, #group_append, #group_by, #group_cube, #group_rollup, #grouping_sets, #hash, #having, #import, #initialize, #insert, #insert_sql, #inspect, #intersect, #invert, #join, #join_clause_sql_append, #join_on_clause_sql_append, #join_table, #join_using_clause_sql_append, #joined_dataset?, #last, #lateral, #limit, #literal_append, #lock_style, #map, #max, #min, #multi_insert, #multi_insert_sql, #naked, #negative_boolean_constant_sql_append, #offset, #or, #order, #order_append, #order_by, #order_more, #order_prepend, #ordered_expression_sql_append, #placeholder_literal_string_sql_append, #prepare, #provides_accurate_rows_matched?, #qualified_identifier_sql_append, #qualify, #quote_identifier_append, #quote_identifiers?, #quote_schema_table_append, #quoted_identifier_append, #recursive_cte_requires_column_aliases?, register_extension, #requires_placeholder_type_specifiers?, #requires_sql_standard_datetimes?, #returning, #reverse, #reverse_order, #row_number_column, #row_proc, #schema_and_table, #select, #select_all, #select_append, #select_group, #select_hash, #select_hash_groups, #select_map, #select_more, #select_order_map, #server, #server?, #set_graph_aliases, #single_record, #single_record!, #single_value, #single_value!, #skip_limit_check, #skip_locked, #split_alias, #split_qualifiers, #sql, #subscript_sql_append, #sum, #supports_cte?, #supports_cte_in_subqueries?, #supports_derived_column_lists?, #supports_distinct_on?, #supports_group_cube?, #supports_group_rollup?, #supports_grouping_sets?, #supports_insert_select?, #supports_intersect_except?, #supports_intersect_except_all?, #supports_is_true?, #supports_join_using?, #supports_lateral_subqueries?, #supports_limits_in_correlated_subqueries?, #supports_modifying_joins?, #supports_multiple_column_in?, #supports_offsets_in_correlated_subqueries?, #supports_ordered_distinct_on?, #supports_regexp?, #supports_replace?, #supports_returning?, #supports_select_all_and_column?, #supports_skip_locked?, #supports_timestamp_timezones?, #supports_timestamp_usecs?, #supports_where_true?, #supports_window_functions?, #to_hash, #to_hash_groups, #truncate, #truncate_sql, #unfiltered, #ungraphed, #ungrouped, #union, #unlimited, #unordered, #unqualified_column_for, #unused_table_alias, #update, #update_sql, #where, #where_all, #where_each, #where_single_value, #window_sql_append, #with, #with_extend, #with_quote_identifiers, #with_recursive, #with_row_proc, #with_sql, #with_sql_all, #with_sql_delete, #with_sql_each, #with_sql_first, #with_sql_insert, #with_sql_single_value

Methods included from SQL::StringMethods

#ilike, #like

Methods included from SQL::OrderMethods

#asc, #desc

Methods included from SQL::NumericMethods

#+, #coerce

Methods included from SQL::ComplexExpressionMethods

#extract, #sql_boolean, #sql_number, #sql_string

Methods included from SQL::CastMethods

#cast, #cast_numeric, #cast_string

Methods included from SQL::BooleanMethods

#~

Methods included from SQL::AliasMethods

#as

Constructor Details

This class inherits a constructor from Sequel::Dataset

Instance Method Details

#fetch_rows(sql) ⇒ Object



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# File 'lib/sequel/adapters/postgres.rb', line 554

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) ⇒ Object

Use a cursor for paging.



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# File 'lib/sequel/adapters/postgres.rb', line 560

def paged_each(opts=OPTS, &block)
  use_cursor(opts).each(&block)
end

#use_cursor(opts = OPTS) ⇒ Object

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.



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# File 'lib/sequel/adapters/postgres.rb', line 586

def use_cursor(opts=OPTS)
  clone(:cursor=>{:rows_per_fetch=>1000}.merge!(opts))
end

#where_current_of(cursor_name = 'sequel_cursor') ⇒ Object

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


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# File 'lib/sequel/adapters/postgres.rb', line 598

def where_current_of(cursor_name='sequel_cursor')
  clone(:where=>Sequel.lit(['CURRENT OF '], Sequel.identifier(cursor_name)))
end