module Sequel::EmulateOffsetWithReverseAndCount
Public Instance Methods
empty?()
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Make empty? work with an offset with an order. By default it would break since the order would be based on a column that empty does not select.
Calls superclass method
# File lib/sequel/adapters/utils/emulate_offset_with_reverse_and_count.rb, line 8 def empty? if o = @opts[:offset] unlimited.count <= o else super end end
select_sql()
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Emulate OFFSET support using reverse order in a subselect, requiring a count of the number of rows.
If offset is used, an order must be provided, since it needs to be reversed in the subselect. Note that the order needs to be unambiguous to work correctly, and you must select all columns that you are ordering on.
Calls superclass method
# File lib/sequel/adapters/utils/emulate_offset_with_reverse_and_count.rb, line 22 def select_sql return super if @opts[:sql] return super unless o = @opts[:offset] order = @opts[:order] || default_offset_order if order.nil? || order.empty? raise(Error, "#{db.database_type} requires an order be provided if using an offset") end ds = unlimited row_count = @opts[:offset_total_count] || ds.clone(:append_sql=>String.new, :placeholder_literal_null=>true).count dsa1 = dataset_alias(1) if o.is_a?(Symbol) && @opts[:bind_vars] && (match = Sequel::Dataset::PreparedStatementMethods::PLACEHOLDER_RE.match(o.to_s)) # Handle use of bound variable offsets. Unfortunately, prepared statement # bound variable offsets cannot be handled, since the bound variable value # isn't available until later. s = match[1].to_sym if prepared_arg?(s) o = prepared_arg(s) end end reverse_offset = row_count - o ds = if reverse_offset > 0 ds.limit(reverse_offset). reverse(*order). from_self(:alias=>dsa1). limit(@opts[:limit]). order(*order) else # Sequel doesn't allow a nonpositive limit. If the offset # is greater than the number of rows, the empty result set # shuld be returned, so use a condition that is always false. ds.where(1=>0) end sql = @opts[:append_sql] || String.new subselect_sql_append(sql, ds) sql end
Private Instance Methods
default_offset_order()
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The default order to use for datasets with offsets, if no order is defined. By default, orders by all of the columns in the dataset.
# File lib/sequel/adapters/utils/emulate_offset_with_reverse_and_count.rb, line 73 def default_offset_order clone(:append_sql=>String.new, :offset=>nil).columns end