139 lines
4.7 KiB
Ruby
139 lines
4.7 KiB
Ruby
# frozen_string_literal: true
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# Keyset::Connection provides cursor based pagination, to avoid using OFFSET.
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# It basically sorts / filters using WHERE sorting_value > cursor.
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# We do this for performance reasons (https://gitlab.com/gitlab-org/gitlab-foss/issues/45756),
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# as well as for having stable pagination
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# https://graphql-ruby.org/pro/cursors.html#whats-the-difference
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# https://coderwall.com/p/lkcaag/pagination-you-re-probably-doing-it-wrong
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#
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# It currently supports sorting on two columns, but the last column must
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# be the primary key. If it's not already included, an order on the
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# primary key will be added automatically, like `order(id: :desc)`
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#
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# Issue.order(created_at: :asc).order(:id)
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# Issue.order(due_date: :asc)
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#
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# You can also use `Gitlab::Database.nulls_last_order`:
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#
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# Issue.reorder(::Gitlab::Database.nulls_last_order('due_date', 'DESC'))
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#
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# It will tolerate non-attribute ordering, but only attributes determine the cursor.
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# For example, this is legitimate:
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#
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# Issue.order('issues.due_date IS NULL').order(due_date: :asc).order(:id)
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#
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# but anything more complex has a chance of not working.
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#
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module Gitlab
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module Graphql
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module Connections
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module Keyset
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class Connection < GraphQL::Relay::BaseConnection
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include Gitlab::Utils::StrongMemoize
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def cursor_from_node(node)
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encoded_json_from_ordering(node)
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end
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def sliced_nodes
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@sliced_nodes ||=
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begin
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OrderInfo.validate_ordering(ordered_nodes, order_list)
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sliced = ordered_nodes
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sliced = slice_nodes(sliced, before, :before) if before.present?
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sliced = slice_nodes(sliced, after, :after) if after.present?
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sliced
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end
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end
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def paged_nodes
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# These are the nodes that will be loaded into memory for rendering
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# So we're ok loading them into memory here as that's bound to happen
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# anyway. Having them ready means we can modify the result while
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# rendering the fields.
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@paged_nodes ||= load_paged_nodes.to_a
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end
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private
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def load_paged_nodes
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if first && last
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raise Gitlab::Graphql::Errors::ArgumentError.new("Can only provide either `first` or `last`, not both")
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end
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if last
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sliced_nodes.last(limit_value)
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else
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sliced_nodes.limit(limit_value) # rubocop: disable CodeReuse/ActiveRecord
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end
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end
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# rubocop: disable CodeReuse/ActiveRecord
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def slice_nodes(sliced, encoded_cursor, before_or_after)
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decoded_cursor = ordering_from_encoded_json(encoded_cursor)
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builder = QueryBuilder.new(arel_table, order_list, decoded_cursor, before_or_after)
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ordering = builder.conditions
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sliced.where(*ordering).where.not(id: decoded_cursor['id'])
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end
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# rubocop: enable CodeReuse/ActiveRecord
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def limit_value
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@limit_value ||= [first, last, max_page_size].compact.min
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end
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def ordered_nodes
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strong_memoize(:order_nodes) do
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unless nodes.primary_key.present?
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raise ArgumentError.new('Relation must have a primary key')
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end
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list = OrderInfo.build_order_list(nodes)
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# ensure there is a primary key ordering
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if list&.last&.attribute_name != nodes.primary_key
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nodes.order(arel_table[nodes.primary_key].desc) # rubocop: disable CodeReuse/ActiveRecord
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else
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nodes
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end
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end
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end
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def order_list
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strong_memoize(:order_list) do
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OrderInfo.build_order_list(ordered_nodes)
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end
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end
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def arel_table
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nodes.arel_table
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end
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# Storing the current order values in the cursor allows us to
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# make an intelligent decision on handling NULL values.
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# Otherwise we would either need to fetch the record first,
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# or fetch it in the SQL, significantly complicating it.
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def encoded_json_from_ordering(node)
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ordering = { 'id' => node[:id].to_s }
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order_list.each do |field|
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field_name = field.attribute_name
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ordering[field_name] = node[field_name].to_s
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end
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encode(ordering.to_json)
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end
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def ordering_from_encoded_json(cursor)
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JSON.parse(decode(cursor))
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rescue JSON::ParserError
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raise Gitlab::Graphql::Errors::ArgumentError, "Please provide a valid cursor"
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end
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end
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end
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end
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end
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end
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