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