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author | arkadiy kraportov <arkadiyk@gmail.com> | 2011-06-09 18:24:54 +0900 |
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committer | arkadiy kraportov <arkadiyk@gmail.com> | 2011-06-09 18:24:54 +0900 |
commit | be48ed3071fd6524d0145c4ad3faeb4aafe3eda3 (patch) | |
tree | f6787fb5bd3dc27db9391cef325b34a4e7b0cf0b /lib/arel | |
parent | 593002080cbcbb6e14acf3bc909aab819811f215 (diff) | |
download | rails-be48ed3071fd6524d0145c4ad3faeb4aafe3eda3.tar.gz rails-be48ed3071fd6524d0145c4ad3faeb4aafe3eda3.tar.bz2 rails-be48ed3071fd6524d0145c4ad3faeb4aafe3eda3.zip |
LIMIT and OFFSET support for MS SQL
Diffstat (limited to 'lib/arel')
-rw-r--r-- | lib/arel/visitors/mssql.rb | 78 |
1 files changed, 69 insertions, 9 deletions
diff --git a/lib/arel/visitors/mssql.rb b/lib/arel/visitors/mssql.rb index ea7ab6394c..713ad0f0f8 100644 --- a/lib/arel/visitors/mssql.rb +++ b/lib/arel/visitors/mssql.rb @@ -3,19 +3,79 @@ module Arel class MSSQL < Arel::Visitors::ToSql private - def build_subselect key, o - stmt = super - core = stmt.cores.first - core.top = Nodes::Top.new(o.limit.expr) if o.limit - stmt + # `top` wouldn't really work here. I.e. User.select("distinct first_name").limit(10) would generate + # "select top 10 distinct first_name from users", which is invalid query! it should be + # "select distinct top 10 first_name from users" + def visit_Arel_Nodes_Top o + "" end - def visit_Arel_Nodes_Limit o - "" + def visit_Arel_Nodes_SelectStatement o + if !o.limit && !o.offset + return super o + end + + select_order_by = "ORDER BY #{o.orders.map { |x| visit x }.join(', ')}" unless o.orders.empty? + + is_select_count = false + sql = o.cores.map { |x| + core_order_by = select_order_by || determine_order_by(x) + if select_count? x + x.projections = [row_num_literal(core_order_by)] + is_select_count = true + else + guard_against_select_constant! x + x.projections << row_num_literal(core_order_by) + end + + visit_Arel_Nodes_SelectCore x + }.join + + sql = "SELECT _t.* FROM (#{sql}) as _t WHERE #{get_offset_limit_clause(o)}" + # fixme count distinct wouldn't work with limit or offset + sql = "SELECT COUNT(1) as count_id FROM (#{sql}) AS subquery" if is_select_count + sql end - def visit_Arel_Nodes_Top o - "TOP #{visit o.expr}" + def get_offset_limit_clause o + first_row = o.offset ? o.offset.expr.to_i + 1 : 1 + last_row = o.limit ? o.limit.expr.to_i - 1 + first_row : nil + if last_row + " _row_num BETWEEN #{first_row} AND #{last_row}" + else + " _row_num >= #{first_row}" + end + end + + def determine_order_by x + unless x.groups.empty? + "ORDER BY #{x.groups.map { |g| visit g }.join ', ' }" + else + "ORDER BY #{find_left_table_pk(x.froms)}" + end + end + + def row_num_literal order_by + Nodes::SqlLiteral.new("ROW_NUMBER() OVER (#{order_by}) as _row_num") + end + + def select_count? x + x.projections.length == 1 && Arel::Nodes::Count === x.projections.first + end + + def guard_against_select_constant! x + # guard against .select(1) (i.e. validate_uniqueness uses it to minimize qry result set) + # todo it won't work for .select('a'), which is probably ok. 'coz of workaround: .select("'a' as a") + x.projections.map! do |p| + p.kind_of?(Fixnum) ? Nodes::SqlLiteral.new("#{p} as _fld_#{p}") : p + end + end + + # fixme raise exception of there is no pk? + # fixme!! Table.primary_key will be depricated. What is the replacement?? + def find_left_table_pk o + return visit o.primary_key if o.instance_of? Arel::Table + find_left_table_pk o.left if o.kind_of? Arel::Nodes::Join end end |