138 lines
4.6 KiB
Ruby
138 lines
4.6 KiB
Ruby
# frozen_string_literal: true
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module Gitlab
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module Pagination
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module Keyset
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# This class transforms the `order()` values from an Activerecord scope into a
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# Gitlab::Pagination::Keyset::Order instance so the query later can be used in
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# keyset pagination.
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#
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# Return values:
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# [transformed_scope, true] # true indicates that the new scope was successfully built
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# [orginal_scope, false] # false indicates that the order values are not supported in this class
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class SimpleOrderBuilder
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def self.build(scope)
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new(scope: scope).build
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end
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def initialize(scope:)
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@scope = scope
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@order_values = scope.order_values
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@model_class = scope.model
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@arel_table = @model_class.arel_table
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@primary_key = @model_class.primary_key
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end
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def build
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order = if order_values.empty?
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primary_key_descending_order
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elsif ordered_by_primary_key?
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primary_key_order
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elsif ordered_by_other_column?
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column_with_tie_breaker_order
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elsif ordered_by_other_column_with_tie_breaker?
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tie_breaker_attribute = order_values.second
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tie_breaker_column_order = Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
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attribute_name: model_class.primary_key,
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order_expression: tie_breaker_attribute
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)
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column_with_tie_breaker_order(tie_breaker_column_order)
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end
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order ? [scope.reorder!(order), true] : [scope, false] # [scope, success]
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end
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private
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attr_reader :scope, :order_values, :model_class, :arel_table, :primary_key
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def primary_key_descending_order
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Gitlab::Pagination::Keyset::Order.build([
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Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
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attribute_name: model_class.primary_key,
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order_expression: arel_table[primary_key].desc
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)
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])
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end
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def primary_key_order
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Gitlab::Pagination::Keyset::Order.build([
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Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
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attribute_name: model_class.primary_key,
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order_expression: order_values.first
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)
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])
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end
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def column_with_tie_breaker_order(tie_breaker_column_order = default_tie_breaker_column_order)
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order_expression = order_values.first
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attribute_name = order_expression.expr.name
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column_nullable = model_class.columns.find { |column| column.name == attribute_name }.null
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nullable = if column_nullable && order_expression.is_a?(Arel::Nodes::Ascending)
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:nulls_last
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elsif column_nullable && order_expression.is_a?(Arel::Nodes::Descending)
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:nulls_first
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else
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:not_nullable
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end
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Gitlab::Pagination::Keyset::Order.build([
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Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
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attribute_name: attribute_name,
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order_expression: order_expression,
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nullable: nullable,
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distinct: false
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),
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tie_breaker_column_order
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])
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end
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def ordered_by_primary_key?
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return unless order_values.one?
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attribute = order_values.first.try(:expr)
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return unless attribute
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arel_table[primary_key].to_s == attribute.to_s
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end
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def ordered_by_other_column?
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return unless order_values.one?
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attribute = order_values.first.try(:expr)
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return unless attribute
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return unless attribute.try(:name)
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model_class.column_names.include?(attribute.name.to_s)
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end
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def ordered_by_other_column_with_tie_breaker?
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return unless order_values.size == 2
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attribute = order_values.first.try(:expr)
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tie_breaker_attribute = order_values.second.try(:expr)
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return unless attribute
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return unless tie_breaker_attribute
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model_class.column_names.include?(attribute.name.to_s) &&
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arel_table[primary_key].to_s == tie_breaker_attribute.to_s
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end
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def default_tie_breaker_column_order
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Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
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attribute_name: model_class.primary_key,
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order_expression: arel_table[primary_key].desc
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)
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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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