gitlab-org--gitlab-foss/lib/gitlab/object_hierarchy.rb
2019-04-05 07:56:21 +08:00

217 lines
7.7 KiB
Ruby

# frozen_string_literal: true
module Gitlab
# Retrieving of parent or child objects based on a base ActiveRecord relation.
#
# This class uses recursive CTEs and as a result will only work on PostgreSQL.
class ObjectHierarchy
DEPTH_COLUMN = :depth
attr_reader :ancestors_base, :descendants_base, :model
# ancestors_base - An instance of ActiveRecord::Relation for which to
# get parent objects.
# descendants_base - An instance of ActiveRecord::Relation for which to
# get child objects. 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 the set of descendants of a given relation, but excluding the given
# relation
# rubocop: disable CodeReuse/ActiveRecord
def descendants
base_and_descendants.where.not(id: descendants_base.select(:id))
end
# rubocop: enable CodeReuse/ActiveRecord
# Returns the maximum depth starting from the base
# A base object with no children has a maximum depth of `1`
def max_descendants_depth
unless hierarchy_supported?
# This makes the return value consistent with the case where hierarchy is supported
return descendants_base.exists? ? 1 : nil
end
base_and_descendants(with_depth: true).maximum(DEPTH_COLUMN)
end
# Returns the set of ancestors of a given relation, but excluding the given
# relation
#
# Passing an `upto` will stop the recursion once the specified parent_id is
# reached. So all ancestors *lower* than the specified ancestor will be
# included.
# rubocop: disable CodeReuse/ActiveRecord
def ancestors(upto: nil, hierarchy_order: nil)
base_and_ancestors(upto: upto, hierarchy_order: hierarchy_order).where.not(id: ancestors_base.select(:id))
end
# rubocop: enable CodeReuse/ActiveRecord
# Returns a relation that includes the ancestors_base set of objects
# and all their ancestors (recursively).
#
# Passing an `upto` will stop the recursion once the specified parent_id is
# reached. So all ancestors *lower* than the specified acestor will be
# included.
#
# Passing a `hierarchy_order` with either `:asc` or `:desc` will cause the
# recursive query order from most nested object to root or from the root
# ancestor to most nested object respectively. This uses a `depth` column
# where `1` is defined as the depth for the base and increment as we go up
# each parent.
# rubocop: disable CodeReuse/ActiveRecord
def base_and_ancestors(upto: nil, hierarchy_order: nil)
return ancestors_base unless hierarchy_supported?
recursive_query = base_and_ancestors_cte(upto, hierarchy_order).apply_to(model.all)
recursive_query = recursive_query.order(depth: hierarchy_order) if hierarchy_order
read_only(recursive_query)
end
# rubocop: enable CodeReuse/ActiveRecord
# Returns a relation that includes the descendants_base set of objects
# and all their descendants (recursively).
#
# When `with_depth` is `true`, a `depth` column is included where it starts with `1` for the base objects
# and incremented as we go down the descendant tree
def base_and_descendants(with_depth: false)
unless hierarchy_supported?
return with_depth ? descendants_base.select("1 as #{DEPTH_COLUMN}", objects_table[Arel.star]) : descendants_base
end
read_only(base_and_descendants_cte(with_depth: with_depth).apply_to(model.all))
end
# Returns a relation that includes the base objects, their ancestors,
# and the descendants of the base objects.
#
# 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 objects are not supported, ancestors_base is returned.
# rubocop: disable CodeReuse/ActiveRecord
def all_objects
return ancestors_base unless hierarchy_supported?
ancestors = base_and_ancestors_cte
descendants = base_and_descendants_cte
ancestors_table = ancestors.alias_to(objects_table)
descendants_table = descendants.alias_to(objects_table)
relation = model
.unscoped
.with
.recursive(ancestors.to_arel, descendants.to_arel)
.from_union([
model.unscoped.from(ancestors_table),
model.unscoped.from(descendants_table)
])
read_only(relation)
end
# rubocop: enable CodeReuse/ActiveRecord
private
def hierarchy_supported?
Gitlab::Database.postgresql?
end
# rubocop: disable CodeReuse/ActiveRecord
def base_and_ancestors_cte(stop_id = nil, hierarchy_order = nil)
cte = SQL::RecursiveCTE.new(:base_and_ancestors)
base_query = ancestors_base.except(:order)
base_query = base_query.select("1 as #{DEPTH_COLUMN}", "ARRAY[id] AS tree_path", "false AS tree_cycle", objects_table[Arel.star]) if hierarchy_order
cte << base_query
# Recursively get all the ancestors of the base set.
parent_query = model
.from([objects_table, cte.table])
.where(objects_table[:id].eq(cte.table[:parent_id]))
.except(:order)
if hierarchy_order
quoted_objects_table_name = model.connection.quote_table_name(objects_table.name)
parent_query = parent_query.select(
cte.table[DEPTH_COLUMN] + 1,
"tree_path || #{quoted_objects_table_name}.id",
"#{quoted_objects_table_name}.id = ANY(tree_path)",
objects_table[Arel.star]
).where(cte.table[:tree_cycle].eq(false))
end
parent_query = parent_query.where(cte.table[:parent_id].not_eq(stop_id)) if stop_id
cte << parent_query
cte
end
# rubocop: enable CodeReuse/ActiveRecord
# rubocop: disable CodeReuse/ActiveRecord
def base_and_descendants_cte(with_depth: false)
cte = SQL::RecursiveCTE.new(:base_and_descendants)
base_query = descendants_base.except(:order)
base_query = base_query.select("1 AS #{DEPTH_COLUMN}", "ARRAY[id] AS tree_path", "false AS tree_cycle", objects_table[Arel.star]) if with_depth
cte << base_query
# Recursively get all the descendants of the base set.
descendants_query = model
.from([objects_table, cte.table])
.where(objects_table[:parent_id].eq(cte.table[:id]))
.except(:order)
if with_depth
quoted_objects_table_name = model.connection.quote_table_name(objects_table.name)
descendants_query = descendants_query.select(
cte.table[DEPTH_COLUMN] + 1,
"tree_path || #{quoted_objects_table_name}.id",
"#{quoted_objects_table_name}.id = ANY(tree_path)",
objects_table[Arel.star]
).where(cte.table[:tree_cycle].eq(false))
end
cte << descendants_query
cte
end
# rubocop: enable CodeReuse/ActiveRecord
def objects_table
model.arel_table
end
def read_only(relation)
# relations using a CTE are not safe to use with update_all as it will
# throw away the CTE, hence we mark them as read-only.
relation.extend(Gitlab::Database::ReadOnlyRelation)
relation
end
end
end