301 lines
11 KiB
Ruby
301 lines
11 KiB
Ruby
# frozen_string_literal: true
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module Gitlab
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# Retrieving of parent or child objects based on a base ActiveRecord relation.
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#
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# This class uses recursive CTEs and as a result will only work on PostgreSQL.
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class ObjectHierarchy
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DEPTH_COLUMN = :depth
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attr_reader :ancestors_base, :descendants_base, :model, :options, :unscoped_model
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# ancestors_base - An instance of ActiveRecord::Relation for which to
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# get parent objects.
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# descendants_base - An instance of ActiveRecord::Relation for which to
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# get child objects. If omitted, ancestors_base is used.
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def initialize(ancestors_base, descendants_base = ancestors_base, options: {})
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raise ArgumentError, "Model of ancestors_base does not match model of descendants_base" if ancestors_base.model != descendants_base.model
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@ancestors_base = ancestors_base
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@descendants_base = descendants_base
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@model = ancestors_base.model
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@unscoped_model = @model.unscoped
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@options = options
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end
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# Returns the set of descendants of a given relation, but excluding the given
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# relation
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# rubocop: disable CodeReuse/ActiveRecord
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def descendants
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base_and_descendants.where.not(id: descendants_base.select(:id))
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end
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# rubocop: enable CodeReuse/ActiveRecord
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# Returns the maximum depth starting from the base
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# A base object with no children has a maximum depth of `1`
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def max_descendants_depth
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base_and_descendants(with_depth: true).maximum(DEPTH_COLUMN)
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end
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# Returns the set of ancestors of a given relation, but excluding the given
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# relation
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#
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# Passing an `upto` will stop the recursion once the specified parent_id is
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# reached. So all ancestors *lower* than the specified ancestor will be
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# included.
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# rubocop: disable CodeReuse/ActiveRecord
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def ancestors(upto: nil, hierarchy_order: nil)
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base_and_ancestors(upto: upto, hierarchy_order: hierarchy_order).where.not(id: ancestors_base.select(:id))
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end
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# rubocop: enable CodeReuse/ActiveRecord
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# Returns a relation that includes the ancestors_base set of objects
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# and all their ancestors (recursively).
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#
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# Passing an `upto` will stop the recursion once the specified parent_id is
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# reached. So all ancestors *lower* than the specified ancestor will be
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# included.
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#
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# Passing a `hierarchy_order` with either `:asc` or `:desc` will cause the
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# recursive query order from most nested object to root or from the root
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# ancestor to most nested object respectively. This uses a `depth` column
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# where `1` is defined as the depth for the base and increment as we go up
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# each parent.
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#
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# Note: By default the order is breadth-first
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# rubocop: disable CodeReuse/ActiveRecord
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def base_and_ancestors(upto: nil, hierarchy_order: nil)
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if use_distinct?
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expose_depth = hierarchy_order.present?
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hierarchy_order ||= :asc
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# if hierarchy_order is given, the calculated `depth` should be present in SELECT
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if expose_depth
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recursive_query = base_and_ancestors_cte(upto, hierarchy_order).apply_to(unscoped_model.all).distinct
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read_only(unscoped_model.from(Arel::Nodes::As.new(recursive_query.arel, objects_table)).order(depth: hierarchy_order))
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else
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recursive_query = base_and_ancestors_cte(upto).apply_to(unscoped_model.all)
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if skip_ordering?
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recursive_query = recursive_query.distinct
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else
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recursive_query = recursive_query.reselect(*recursive_query.arel.projections, 'ROW_NUMBER() OVER () as depth').distinct
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recursive_query = unscoped_model.from(Arel::Nodes::As.new(recursive_query.arel, objects_table))
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recursive_query = remove_depth_and_maintain_order(recursive_query, hierarchy_order: hierarchy_order)
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end
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read_only(recursive_query)
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end
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else
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recursive_query = base_and_ancestors_cte(upto, hierarchy_order).apply_to(unscoped_model.all)
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recursive_query = recursive_query.order(depth: hierarchy_order) if hierarchy_order
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read_only(recursive_query)
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end
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end
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# rubocop: enable CodeReuse/ActiveRecord
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# Returns a relation that includes the descendants_base set of objects
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# and all their descendants (recursively).
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#
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# When `with_depth` is `true`, a `depth` column is included where it starts with `1` for the base objects
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# and incremented as we go down the descendant tree
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# rubocop: disable CodeReuse/ActiveRecord
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def base_and_descendants(with_depth: false)
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if use_distinct?
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# Always calculate `depth`, remove it later if with_depth is false
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if with_depth
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base_cte = base_and_descendants_cte(with_depth: true).apply_to(unscoped_model.all).distinct
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read_only(unscoped_model.from(Arel::Nodes::As.new(base_cte.arel, objects_table)).order(depth: :asc))
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else
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base_cte = base_and_descendants_cte.apply_to(unscoped_model.all)
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if skip_ordering?
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base_cte = base_cte.distinct
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else
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base_cte = base_cte.reselect(*base_cte.arel.projections, 'ROW_NUMBER() OVER () as depth').distinct
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base_cte = unscoped_model.from(Arel::Nodes::As.new(base_cte.arel, objects_table))
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base_cte = remove_depth_and_maintain_order(base_cte, hierarchy_order: :asc)
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end
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read_only(base_cte)
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end
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else
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read_only(base_and_descendants_cte(with_depth: with_depth).apply_to(unscoped_model.all))
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end
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end
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# rubocop: enable CodeReuse/ActiveRecord
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# Returns a relation that includes the base objects, their ancestors,
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# and the descendants of the base objects.
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#
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# The resulting query will roughly look like the following:
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#
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# WITH RECURSIVE ancestors AS ( ... ),
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# descendants AS ( ... )
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# SELECT *
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# FROM (
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# SELECT *
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# FROM ancestors namespaces
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#
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# UNION
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#
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# SELECT *
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# FROM descendants namespaces
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# ) groups;
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#
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# Using this approach allows us to further add criteria to the relation with
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# Rails thinking it's selecting data the usual way.
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#
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# If nested objects are not supported, ancestors_base is returned.
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# rubocop: disable CodeReuse/ActiveRecord
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def all_objects
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ancestors = base_and_ancestors_cte
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descendants = base_and_descendants_cte
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ancestors_table = ancestors.alias_to(objects_table)
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descendants_table = descendants.alias_to(objects_table)
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ancestors_scope = unscoped_model.from(ancestors_table)
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descendants_scope = unscoped_model.from(descendants_table)
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if use_distinct?
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ancestors_scope = ancestors_scope.distinct
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descendants_scope = descendants_scope.distinct
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end
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relation = unscoped_model
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.with
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.recursive(ancestors.to_arel, descendants.to_arel)
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.from_union([
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ancestors_scope,
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descendants_scope
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])
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read_only(relation)
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end
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# rubocop: enable CodeReuse/ActiveRecord
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private
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# Use distinct on the Namespace queries to avoid bad planner behavior in PG11.
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def use_distinct?
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return unless model <= Namespace
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# Global use_distinct_for_all_object_hierarchy takes precedence over use_distinct_in_object_hierarchy
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return true if Feature.enabled?(:use_distinct_for_all_object_hierarchy)
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return options[:use_distinct] if options.key?(:use_distinct)
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false
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end
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# Skips the extra ordering when using distinct on the namespace queries
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def skip_ordering?
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return options[:skip_ordering] if options.key?(:skip_ordering)
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false
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end
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# Remove the extra `depth` field using an INNER JOIN to avoid breaking UNION queries
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# and ordering the rows based on the `depth` column to maintain the row order.
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#
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# rubocop: disable CodeReuse/ActiveRecord
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def remove_depth_and_maintain_order(relation, hierarchy_order: :asc)
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joined_relation = model.joins("INNER JOIN (#{relation.select(:id, :depth).to_sql}) namespaces_join_table on namespaces_join_table.id = #{model.table_name}.id").order("namespaces_join_table.depth" => hierarchy_order)
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model.from(Arel::Nodes::As.new(joined_relation.arel, objects_table))
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end
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# rubocop: enable CodeReuse/ActiveRecord
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# rubocop: disable CodeReuse/ActiveRecord
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def base_and_ancestors_cte(stop_id = nil, hierarchy_order = nil)
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cte = SQL::RecursiveCTE.new(:base_and_ancestors)
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base_query = ancestors_base.except(:order)
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base_query = base_query.select("1 as #{DEPTH_COLUMN}", "ARRAY[#{objects_table.name}.id] AS tree_path", "false AS tree_cycle", objects_table[Arel.star]) if hierarchy_order
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cte << base_query
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# Recursively get all the ancestors of the base set.
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parent_query = unscoped_model
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.from(from_tables(cte))
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.where(ancestor_conditions(cte))
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.except(:order)
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if hierarchy_order
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quoted_objects_table_name = model.connection.quote_table_name(objects_table.name)
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parent_query = parent_query.select(
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cte.table[DEPTH_COLUMN] + 1,
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"tree_path || #{quoted_objects_table_name}.id",
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"#{quoted_objects_table_name}.id = ANY(tree_path)",
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objects_table[Arel.star]
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).where(cte.table[:tree_cycle].eq(false))
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end
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parent_query = parent_query.where(parent_id_column(cte).not_eq(stop_id)) if stop_id
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cte << parent_query
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cte
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end
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# rubocop: enable CodeReuse/ActiveRecord
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# rubocop: disable CodeReuse/ActiveRecord
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def base_and_descendants_cte(with_depth: false)
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cte = SQL::RecursiveCTE.new(:base_and_descendants)
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base_query = descendants_base.except(:order)
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base_query = base_query.select("1 AS #{DEPTH_COLUMN}", "ARRAY[#{objects_table.name}.id] AS tree_path", "false AS tree_cycle", objects_table[Arel.star]) if with_depth
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cte << base_query
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# Recursively get all the descendants of the base set.
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descendants_query = unscoped_model
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.from(from_tables(cte))
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.where(descendant_conditions(cte))
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.except(:order)
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if with_depth
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quoted_objects_table_name = model.connection.quote_table_name(objects_table.name)
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descendants_query = descendants_query.select(
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cte.table[DEPTH_COLUMN] + 1,
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"tree_path || #{quoted_objects_table_name}.id",
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"#{quoted_objects_table_name}.id = ANY(tree_path)",
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objects_table[Arel.star]
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).where(cte.table[:tree_cycle].eq(false))
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end
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cte << descendants_query
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cte
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end
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# rubocop: enable CodeReuse/ActiveRecord
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def objects_table
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model.arel_table
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end
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def parent_id_column(cte)
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cte.table[:parent_id]
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end
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def from_tables(cte)
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[objects_table, cte.table]
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end
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def ancestor_conditions(cte)
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objects_table[:id].eq(cte.table[:parent_id])
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end
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def descendant_conditions(cte)
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objects_table[:parent_id].eq(cte.table[:id])
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end
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def read_only(relation)
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# relations using a CTE are not safe to use with update_all as it will
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# throw away the CTE, hence we mark them as read-only.
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relation.extend(Gitlab::Database::ReadOnlyRelation)
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relation
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end
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end
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end
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Gitlab::ObjectHierarchy.prepend_mod_with('Gitlab::ObjectHierarchy')
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