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module Arel
module Visitors
class MSSQL < Arel::Visitors::ToSql
RowNumber = Struct.new :children
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, collector
collector << "ROW_NUMBER() OVER (ORDER BY "
inject_join(o.children, collector, ', ') << ") as _row_num"
end
def visit_Arel_Nodes_SelectStatement o, collector
if !o.limit && !o.offset
return super
end
is_select_count = false
o.cores.each { |x|
core_order_by = row_num_literal determine_order_by(o.orders, x)
if select_count? x
x.projections = [core_order_by]
is_select_count = true
else
x.projections << core_order_by
end
}
if is_select_count
# fixme count distinct wouldn't work with limit or offset
collector << "SELECT COUNT(1) as count_id FROM ("
end
collector << "SELECT _t.* FROM ("
collector = o.cores.inject(collector) { |c,x|
visit_Arel_Nodes_SelectCore x, c
}
collector << ") as _t WHERE #{get_offset_limit_clause(o)}"
if is_select_count
collector << ") AS subquery"
else
collector
end
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?
orders
elsif x.groups.any?
x.groups
else
pk = find_left_table_pk(x.froms)
pk ? [pk] : []
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 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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