236 lines
9 KiB
Ruby
236 lines
9 KiB
Ruby
# frozen_string_literal: true
|
|
|
|
module Gitlab
|
|
module Pagination
|
|
module Keyset
|
|
# This class stores information for one column (or SQL expression) which can be used in an
|
|
# ORDER BY SQL clasue.
|
|
# The goal of this class is to encapsulate all the metadata in one place which are needed to
|
|
# make keyset pagination work in a generalized way.
|
|
#
|
|
# == Arguments
|
|
#
|
|
# **order expression** (Arel::Nodes::Node | String)
|
|
#
|
|
# The actual SQL expression for the ORDER BY clause.
|
|
#
|
|
# Examples:
|
|
# # Arel column order definition
|
|
# Project.arel_table[:id].asc # ORDER BY projects.id ASC
|
|
#
|
|
# # Arel expression, calculated order definition
|
|
# Arel::Nodes::NamedFunction.new("COALESCE", [Project.arel_table[:issue_count].asc, 0]).asc # ORDER BY COALESCE(projects.issue_count, 0)
|
|
#
|
|
# # Another Arel expression
|
|
# Arel::Nodes::Multiplication(Issue.arel_table[:weight], Issue.arel_table[:time_spent]).desc
|
|
#
|
|
# # Raw string order definition
|
|
# 'issues.type DESC NULLS LAST'
|
|
#
|
|
# **column_expression** (Arel::Nodes::Node | String)
|
|
#
|
|
# Expression for the database column or an expression. This value will be used with logical operations (>, <, =, !=)
|
|
# when building the database query for the next page.
|
|
#
|
|
# Examples:
|
|
# # Arel column reference
|
|
# Issue.arel_table[:title]
|
|
#
|
|
# # Calculated value
|
|
# Arel::Nodes::Multiplication(Issue.arel_table[:weight], Issue.arel_table[:time_spent])
|
|
#
|
|
# **attribute_name** (String | Symbol)
|
|
#
|
|
# An attribute on the loaded ActiveRecord model where the value can be obtained.
|
|
#
|
|
# Examples:
|
|
# # Simple attribute definition
|
|
# attribute_name = :title
|
|
#
|
|
# # Later on this attribute will be used like this:
|
|
# my_record = Issue.find(x)
|
|
# value = my_record[attribute_name] # reads data from the title column
|
|
#
|
|
# # Calculated value based on an Arel or raw SQL expression
|
|
#
|
|
# attribute_name = :lowercase_title
|
|
#
|
|
# # `lowercase_title` is not is not a table column therefore we need to make sure it's available in the `SELECT` clause
|
|
#
|
|
# my_record = Issue.select(:id, 'LOWER(title) as lowercase_title').last
|
|
# value = my_record[:lowercase_title]
|
|
#
|
|
# **distinct**
|
|
#
|
|
# Boolean value.
|
|
#
|
|
# Tells us whether the database column contains only distinct values. If the column is covered by
|
|
# a unique index then set to true.
|
|
#
|
|
# **nullable** (:not_nullable | :nulls_last | :nulls_first)
|
|
#
|
|
# Tells us whether the database column is nullable or not. This information can be
|
|
# obtained from the DB schema.
|
|
#
|
|
# If the column is not nullable, set this attribute to :not_nullable.
|
|
#
|
|
# If the column is nullable, then additional information is needed. Based on the ordering, the null values
|
|
# will show up at the top or at the bottom of the resultset.
|
|
#
|
|
# Examples:
|
|
# # Nulls are showing up at the top (for example: ORDER BY column ASC):
|
|
# nullable = :nulls_first
|
|
#
|
|
# # Nulls are showing up at the bottom (for example: ORDER BY column DESC):
|
|
# nullable = :nulls_last
|
|
#
|
|
# **order_direction**
|
|
#
|
|
# :asc or :desc
|
|
#
|
|
# Note: this is an optional attribute, the value will be inferred from the order_expression.
|
|
# Sometimes it's not possible to infer the order automatically. In this case an exception will be
|
|
# raised (when the query is executed). If the reverse order cannot be computed, it must be provided explicitly.
|
|
#
|
|
# **reversed_order_expression**
|
|
#
|
|
# The reversed version of the order_expression.
|
|
#
|
|
# A ColumnOrderDefinition object is able to reverse itself which is used when paginating backwards.
|
|
# When a complex order_expression is provided (raw string), then reversing the order automatically
|
|
# is not possible. In this case an exception will be raised.
|
|
#
|
|
# Example:
|
|
#
|
|
# order_expression = Project.arel_table[:id].asc
|
|
# reversed_order_expression = Project.arel_table[:id].desc
|
|
#
|
|
# **add_to_projections**
|
|
#
|
|
# Set to true if the column is not part of the queried table. (Not part of SELECT *)
|
|
#
|
|
# Example:
|
|
#
|
|
# - When the order is a calculated expression or the column is in another table (JOIN-ed)
|
|
#
|
|
# If the add_to_projections is true, the query builder will automatically add the column to the SELECT values
|
|
class ColumnOrderDefinition
|
|
REVERSED_ORDER_DIRECTIONS = { asc: :desc, desc: :asc }.freeze
|
|
REVERSED_NULL_POSITIONS = { nulls_first: :nulls_last, nulls_last: :nulls_first }.freeze
|
|
AREL_ORDER_CLASSES = { Arel::Nodes::Ascending => :asc, Arel::Nodes::Descending => :desc }.freeze
|
|
ALLOWED_NULLABLE_VALUES = [:not_nullable, :nulls_first, :nulls_last].freeze
|
|
|
|
attr_reader :attribute_name, :column_expression, :order_expression, :add_to_projections, :order_direction
|
|
|
|
def initialize(attribute_name:, order_expression:, column_expression: nil, reversed_order_expression: nil, nullable: :not_nullable, distinct: true, order_direction: nil, add_to_projections: false)
|
|
@attribute_name = attribute_name
|
|
@order_expression = order_expression
|
|
@column_expression = column_expression || calculate_column_expression(order_expression)
|
|
@distinct = distinct
|
|
@reversed_order_expression = reversed_order_expression || calculate_reversed_order(order_expression)
|
|
@nullable = parse_nullable(nullable, distinct)
|
|
@order_direction = parse_order_direction(order_expression, order_direction)
|
|
@add_to_projections = add_to_projections
|
|
end
|
|
|
|
def reverse
|
|
self.class.new(
|
|
attribute_name: attribute_name,
|
|
column_expression: column_expression,
|
|
order_expression: reversed_order_expression,
|
|
reversed_order_expression: order_expression,
|
|
nullable: not_nullable? ? :not_nullable : REVERSED_NULL_POSITIONS[nullable],
|
|
distinct: distinct,
|
|
order_direction: REVERSED_ORDER_DIRECTIONS[order_direction]
|
|
)
|
|
end
|
|
|
|
def ascending_order?
|
|
order_direction == :asc
|
|
end
|
|
|
|
def descending_order?
|
|
order_direction == :desc
|
|
end
|
|
|
|
def nulls_first?
|
|
nullable == :nulls_first
|
|
end
|
|
|
|
def nulls_last?
|
|
nullable == :nulls_last
|
|
end
|
|
|
|
def not_nullable?
|
|
nullable == :not_nullable
|
|
end
|
|
|
|
def nullable?
|
|
!not_nullable?
|
|
end
|
|
|
|
def distinct?
|
|
distinct
|
|
end
|
|
|
|
def order_direction_as_sql_string
|
|
sql_string = ascending_order? ? +'ASC' : +'DESC'
|
|
|
|
if nulls_first?
|
|
sql_string << ' NULLS FIRST'
|
|
elsif nulls_last?
|
|
sql_string << ' NULLS LAST'
|
|
end
|
|
|
|
sql_string
|
|
end
|
|
|
|
private
|
|
|
|
attr_reader :reversed_order_expression, :nullable, :distinct
|
|
|
|
def calculate_reversed_order(order_expression)
|
|
unless AREL_ORDER_CLASSES.has_key?(order_expression.class) # Arel can reverse simple orders
|
|
raise "Couldn't determine reversed order for `#{order_expression}`, please provide the `reversed_order_expression` parameter."
|
|
end
|
|
|
|
order_expression.reverse
|
|
end
|
|
|
|
def calculate_column_expression(order_expression)
|
|
if order_expression.respond_to?(:expr)
|
|
order_expression.expr
|
|
else
|
|
raise("Couldn't calculate the column expression. Please pass an ARel node as the order_expression, not a string.")
|
|
end
|
|
end
|
|
|
|
def parse_order_direction(order_expression, order_direction)
|
|
transformed_order_direction = if order_direction.nil? && AREL_ORDER_CLASSES[order_expression.class]
|
|
AREL_ORDER_CLASSES[order_expression.class]
|
|
elsif order_direction.present?
|
|
order_direction.to_s.downcase.to_sym
|
|
end
|
|
|
|
unless REVERSED_ORDER_DIRECTIONS.has_key?(transformed_order_direction)
|
|
raise "Invalid or missing `order_direction` (value: #{order_direction}) was given, the allowed values are: :asc or :desc"
|
|
end
|
|
|
|
transformed_order_direction
|
|
end
|
|
|
|
def parse_nullable(nullable, distinct)
|
|
if ALLOWED_NULLABLE_VALUES.exclude?(nullable)
|
|
raise "Invalid `nullable` is given (value: #{nullable}), the allowed values are: #{ALLOWED_NULLABLE_VALUES.join(', ')}"
|
|
end
|
|
|
|
if nullable != :not_nullable && distinct
|
|
raise 'Invalid column definition, `distinct` and `nullable` columns are not allowed at the same time'
|
|
end
|
|
|
|
nullable
|
|
end
|
|
end
|
|
end
|
|
end
|
|
end
|