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module Gitlab
# Retrieving of parent or child groups based on a base ActiveRecord relation.
#
# This class uses recursive CTEs and as a result will only work on PostgreSQL.
class GroupHierarchy
attr_reader :ancestors_base, :descendants_base, :model
# ancestors_base - An instance of ActiveRecord::Relation for which to
# get parent groups.
# descendants_base - An instance of ActiveRecord::Relation for which to
# get child groups. If omitted, ancestors_base is used.
def initialize(ancestors_base, descendants_base = ancestors_base)
raise ArgumentError.new("Model of ancestors_base does not match model of descendants_base") if ancestors_base.model != descendants_base.model
@ancestors_base = ancestors_base
@descendants_base = descendants_base
@model = ancestors_base.model
end
# Returns a relation that includes the ancestors_base set of groups
# and all their ancestors (recursively).
def base_and_ancestors
return ancestors_base unless Group.supports_nested_groups?
base_and_ancestors_cte.apply_to(model.all)
end
# Returns a relation that includes the descendants_base set of groups
# and all their descendants (recursively).
def base_and_descendants
return descendants_base unless Group.supports_nested_groups?
base_and_descendants_cte.apply_to(model.all)
end
# Returns a relation that includes the base groups, their ancestors,
# and the descendants of the base groups.
#
# The resulting query will roughly look like the following:
#
# WITH RECURSIVE ancestors AS ( ... ),
# descendants AS ( ... )
# SELECT *
# FROM (
# SELECT *
# FROM ancestors namespaces
#
# UNION
#
# SELECT *
# FROM descendants namespaces
# ) groups;
#
# Using this approach allows us to further add criteria to the relation with
# Rails thinking it's selecting data the usual way.
#
# If nested groups are not supported, ancestors_base is returned.
def all_groups
return ancestors_base unless Group.supports_nested_groups?
ancestors = base_and_ancestors_cte
descendants = base_and_descendants_cte
ancestors_table = ancestors.alias_to(groups_table)
descendants_table = descendants.alias_to(groups_table)
union = SQL::Union.new([model.unscoped.from(ancestors_table),
model.unscoped.from(descendants_table)])
model
.unscoped
.with
.recursive(ancestors.to_arel, descendants.to_arel)
.from("(#{union.to_sql}) #{model.table_name}")
end
private
def base_and_ancestors_cte
cte = SQL::RecursiveCTE.new(:base_and_ancestors)
cte << ancestors_base.except(:order)
# Recursively get all the ancestors of the base set.
cte << model
.from([groups_table, cte.table])
.where(groups_table[:id].eq(cte.table[:parent_id]))
.except(:order)
cte
end
def base_and_descendants_cte
cte = SQL::RecursiveCTE.new(:base_and_descendants)
cte << descendants_base.except(:order)
# Recursively get all the descendants of the base set.
cte << model
.from([groups_table, cte.table])
.where(groups_table[:parent_id].eq(cte.table[:id]))
.except(:order)
cte
end
def groups_table
model.arel_table
end
end
end
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