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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
# We need to run 'compact' because 'nil' is not removed from order_values
# in some cases due to the use of 'default_scope'.
@order_values = scope.order_values.compact
@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)
# Ordered by a primary key. Ex. 'ORDER BY id'.
elsif ordered_by_primary_key?
primary_key_order
# Ordered by one non-primary table column. Ex. 'ORDER BY created_at'.
elsif ordered_by_other_column?
column_with_tie_breaker_order
# Ordered by two table columns with the last column as a tie breaker. Ex. 'ORDER BY created, id ASC'.
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 table_column?(name)
model_class.column_names.include?(name.to_s)
end
def primary_key?(attribute)
arel_table[primary_key].to_s == attribute.to_s
end
def lower_named_function?(attribute)
attribute.is_a?(Arel::Nodes::NamedFunction) && attribute.name&.downcase == 'lower'
end
def arel_nulls?(order_value)
return unless order_value.is_a?(Arel::Nodes::NullsLast) || order_value.is_a?(Arel::Nodes::NullsFirst)
column_name = order_value.try(:expr).try(:expr).try(:name)
table_column?(column_name)
end
def supported_column?(order_value)
return true if arel_nulls?(order_value)
attribute = order_value.try(:expr)
return unless attribute
if lower_named_function?(attribute)
attribute.expressions.one? && attribute.expressions.first.respond_to?(:name) && table_column?(attribute.expressions.first.name)
else
attribute.respond_to?(:name) && table_column?(attribute.name)
end
end
def nullability(order_value, attribute_name)
nullable = model_class.columns.find { |column| column.name == attribute_name }.null
if nullable && order_value.is_a?(Arel::Nodes::Ascending)
:nulls_last
elsif nullable && order_value.is_a?(Arel::Nodes::Descending)
:nulls_first
else
:not_nullable
end
end
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)
Gitlab::Pagination::Keyset::Order.build(
[
column(order_values.first),
tie_breaker_column_order
])
end
def column(order_value)
return nulls_order_column(order_value) if arel_nulls?(order_value)
return lower_named_function_column(order_value) if lower_named_function?(order_value.expr)
attribute_name = order_value.expr.name
Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
attribute_name: attribute_name,
order_expression: order_value,
nullable: nullability(order_value, attribute_name),
distinct: false
)
end
def nulls_order_column(order_value)
attribute = order_value.expr.expr
Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
attribute_name: attribute.name,
column_expression: attribute,
order_expression: order_value,
reversed_order_expression: order_value.reverse,
order_direction: order_value.expr.direction,
nullable: order_value.is_a?(Arel::Nodes::NullsLast) ? :nulls_last : :nulls_first,
distinct: false
)
end
def lower_named_function_column(order_value)
attribute_name = order_value.expr.expressions.first.name
Gitlab::Pagination::Keyset::ColumnOrderDefinition.new(
attribute_name: attribute_name,
column_expression: Arel::Nodes::NamedFunction.new("LOWER", [model_class.arel_table[attribute_name]]),
order_expression: order_value,
nullable: nullability(order_value, attribute_name),
distinct: false
)
end
def ordered_by_primary_key?
return unless order_values.one?
attribute = order_values.first.try(:expr)
attribute && primary_key?(attribute)
end
def ordered_by_other_column?
return unless order_values.one?
supported_column?(order_values.first)
end
def ordered_by_other_column_with_tie_breaker?
return unless order_values.size == 2
return unless supported_column?(order_values.first)
tie_breaker_attribute = order_values.second.try(:expr)
tie_breaker_attribute && primary_key?(tie_breaker_attribute)
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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