diff options
Diffstat (limited to 'lib/gitlab/sql/recursive_cte.rb')
-rw-r--r-- | lib/gitlab/sql/recursive_cte.rb | 62 |
1 files changed, 62 insertions, 0 deletions
diff --git a/lib/gitlab/sql/recursive_cte.rb b/lib/gitlab/sql/recursive_cte.rb new file mode 100644 index 00000000000..5b1b03820a3 --- /dev/null +++ b/lib/gitlab/sql/recursive_cte.rb @@ -0,0 +1,62 @@ +module Gitlab + module SQL + # Class for easily building recursive CTE statements. + # + # Example: + # + # cte = RecursiveCTE.new(:my_cte_name) + # ns = Arel::Table.new(:namespaces) + # + # cte << Namespace. + # where(ns[:parent_id].eq(some_namespace_id)) + # + # cte << Namespace. + # from([ns, cte.table]). + # where(ns[:parent_id].eq(cte.table[:id])) + # + # Namespace.with. + # recursive(cte.to_arel). + # from(cte.alias_to(ns)) + class RecursiveCTE + attr_reader :table + + # name - The name of the CTE as a String or Symbol. + def initialize(name) + @table = Arel::Table.new(name) + @queries = [] + end + + # Adds a query to the body of the CTE. + # + # relation - The relation object to add to the body of the CTE. + def <<(relation) + @queries << relation + end + + # Returns the Arel relation for this CTE. + def to_arel + sql = Arel::Nodes::SqlLiteral.new(Union.new(@queries).to_sql) + + Arel::Nodes::As.new(table, Arel::Nodes::Grouping.new(sql)) + end + + # Returns an "AS" statement that aliases the CTE name as the given table + # name. This allows one to trick ActiveRecord into thinking it's selecting + # from an actual table, when in reality it's selecting from a CTE. + # + # alias_table - The Arel table to use as the alias. + def alias_to(alias_table) + Arel::Nodes::As.new(table, alias_table) + end + + # Applies the CTE to the given relation, returning a new one that will + # query from it. + def apply_to(relation) + relation.except(:where). + with. + recursive(to_arel). + from(alias_to(relation.model.arel_table)) + end + end + end +end |