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module Arel
module Visitors
class MSSQL < Arel::Visitors::ToSql
class RowNumber
attr_reader :expr
def initialize node
@expr = node
end
end
private
# `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_Visitors_MSSQL_RowNumber o
"ROW_NUMBER() OVER (#{o.expr}) as _row_num"
end
def visit_Arel_Nodes_SelectStatement o
if !o.limit && !o.offset
return super o
end
is_select_count = false
sql = o.cores.map { |x|
core_order_by = determine_order_by(o.orders, x)
if select_count? x
x.projections = [row_num_literal(core_order_by)]
is_select_count = true
else
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 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 orders, x
if orders.any?
"ORDER BY #{orders.map { |x| visit x }.join(', ')}"
else
if x.groups.any?
"ORDER BY #{x.groups.map { |g| visit g }.join ', ' }"
else
"ORDER BY #{find_left_table_pk(x.froms)}"
end
end
end
def row_num_literal order_by
RowNumber.new order_by
end
def select_count? x
x.projections.length == 1 && Arel::Nodes::Count === x.projections.first
end
# FIXME raise exception of there is no pk?
# FIXME!! Table.primary_key will be deprecated. 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
end
end
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