debian-mirror-gitlab/lib/api/helpers/pagination.rb

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module API
module Helpers
module Pagination
def paginate(relation)
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strategy = if params[:pagination] == 'keyset' && Feature.enabled?('api_keyset_pagination')
KeysetPaginationStrategy
else
DefaultPaginationStrategy
end
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strategy.new(self).paginate(relation)
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end
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class KeysetPaginationInfo
attr_reader :relation, :request_context
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def initialize(relation, request_context)
# This is because it's rather complex to support multiple values with possibly different sort directions
# (and we don't need this in the API)
if relation.order_values.size > 1
raise "Pagination only supports ordering by a single column." \
"The following columns were given: #{relation.order_values.map { |v| v.expr.name }}"
end
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@relation = relation
@request_context = request_context
end
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def fields
keys.zip(values).reject { |_, v| v.nil? }.to_h
end
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def column_for_order_by(relation)
relation.order_values.first&.expr&.name
end
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# Sort direction (`:asc` or `:desc`)
def sort
@sort ||= if order_by_primary_key?
# Default order is by id DESC
:desc
else
# API defaults to DESC order if param `sort` not present
request_context.params[:sort]&.to_sym || :desc
end
end
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# Do we only sort by primary key?
def order_by_primary_key?
keys.size == 1 && keys.first == primary_key
end
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def primary_key
relation.model.primary_key.to_sym
end
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def sort_ascending?
sort == :asc
end
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# Build hash of request parameters for a given record (relevant to pagination)
def params_for(record)
return {} unless record
keys.each_with_object({}) do |key, h|
h["ks_prev_#{key}".to_sym] = record.attributes[key.to_s]
end
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end
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private
# All values present in request parameters that correspond to #keys.
def values
@values ||= keys.map do |key|
request_context.params["ks_prev_#{key}".to_sym]
end
end
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# All keys relevant to pagination.
# This always includes the primary key. Optionally, the `order_by` key is prepended.
def keys
@keys ||= [column_for_order_by(relation), primary_key].compact.uniq
end
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end
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class KeysetPaginationStrategy
attr_reader :request_context
delegate :params, :header, :request, to: :request_context
def initialize(request_context)
@request_context = request_context
end
def paginate(relation)
pagination = KeysetPaginationInfo.new(relation, request_context)
paged_relation = relation.limit(per_page)
if conds = conditions(pagination)
paged_relation = paged_relation.where(*conds)
end
# In all cases: sort by primary key (possibly in addition to another sort column)
paged_relation = paged_relation.order(pagination.primary_key => pagination.sort)
add_default_pagination_headers
if last_record = paged_relation.last
next_page_params = pagination.params_for(last_record)
add_navigation_links(next_page_params)
end
paged_relation
end
private
def conditions(pagination)
fields = pagination.fields
return nil if fields.empty?
placeholder = fields.map { '?' }
comp = if pagination.sort_ascending?
'>'
else
'<'
end
[
# Row value comparison:
# (A, B) < (a, b) <=> (A < a) OR (A = a AND B < b)
# <=> A <= a AND ((A < a) OR (A = a AND B < b))
"(#{fields.keys.join(',')}) #{comp} (#{placeholder.join(',')})",
*fields.values
]
end
def per_page
params[:per_page]
end
def add_default_pagination_headers
header 'X-Per-Page', per_page.to_s
end
def add_navigation_links(next_page_params)
header 'X-Next-Page', page_href(next_page_params)
header 'Link', link_for('next', next_page_params)
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end
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def page_href(next_page_params)
request_url = request.url.split('?').first
request_params = params.dup
request_params[:per_page] = per_page
request_params.merge!(next_page_params) if next_page_params
"#{request_url}?#{request_params.to_query}"
end
def link_for(rel, next_page_params)
%(<#{page_href(next_page_params)}>; rel="#{rel}")
end
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end
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class DefaultPaginationStrategy
attr_reader :request_context
delegate :params, :header, :request, to: :request_context
def initialize(request_context)
@request_context = request_context
end
def paginate(relation)
relation = add_default_order(relation)
relation.page(params[:page]).per(params[:per_page]).tap do |data|
add_pagination_headers(data)
end
end
private
def add_default_order(relation)
if relation.is_a?(ActiveRecord::Relation) && relation.order_values.empty?
relation = relation.order(:id)
end
relation
end
def add_pagination_headers(paginated_data)
header 'X-Per-Page', paginated_data.limit_value.to_s
header 'X-Page', paginated_data.current_page.to_s
header 'X-Next-Page', paginated_data.next_page.to_s
header 'X-Prev-Page', paginated_data.prev_page.to_s
header 'Link', pagination_links(paginated_data)
return if data_without_counts?(paginated_data)
header 'X-Total', paginated_data.total_count.to_s
header 'X-Total-Pages', total_pages(paginated_data).to_s
end
def pagination_links(paginated_data)
request_url = request.url.split('?').first
request_params = params.clone
request_params[:per_page] = paginated_data.limit_value
links = []
request_params[:page] = paginated_data.prev_page
links << %(<#{request_url}?#{request_params.to_query}>; rel="prev") if request_params[:page]
request_params[:page] = paginated_data.next_page
links << %(<#{request_url}?#{request_params.to_query}>; rel="next") if request_params[:page]
request_params[:page] = 1
links << %(<#{request_url}?#{request_params.to_query}>; rel="first")
unless data_without_counts?(paginated_data)
request_params[:page] = total_pages(paginated_data)
links << %(<#{request_url}?#{request_params.to_query}>; rel="last")
end
links.join(', ')
end
def total_pages(paginated_data)
# Ensure there is in total at least 1 page
[paginated_data.total_pages, 1].max
end
def data_without_counts?(paginated_data)
paginated_data.is_a?(Kaminari::PaginatableWithoutCount)
end
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end
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end
end
end