Andreas Brandl
parent
cc1d141127
commit
f8aee5b086
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@ -2,15 +2,175 @@ module API
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module Helpers
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module Pagination
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def paginate(relation)
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DefaultPaginationStrategy.new(self).paginate(relation)
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strategy = if params[:pagination] == 'keyset'
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KeysetPaginationStrategy
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else
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DefaultPaginationStrategy
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end
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strategy.new(self).paginate(relation)
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end
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class KeysetPaginationInfo
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attr_reader :relation, :request_context
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def initialize(relation, request_context)
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# This is because it's rather complex to support multiple values with possibly different sort directions
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# (and we don't need this in the API)
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if relation.order_values.size > 1
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raise "Pagination only supports ordering by a single column." \
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"The following columns were given: #{relation.order_values.map { |v| v.expr.name }}"
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end
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@relation = relation
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@request_context = request_context
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end
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def fields
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keys.zip(values).reject { |_, v| v.nil? }.to_h
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end
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def column_for_order_by(relation)
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relation.order_values.first&.expr&.name
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end
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# Sort direction (`:asc` or `:desc`)
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def sort
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@sort ||= if order_by_primary_key?
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# Default order is by id DESC
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:desc
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else
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# API defaults to DESC order if param `sort` not present
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request_context.params[:sort]&.to_sym || :desc
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end
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end
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# Do we only sort by primary key?
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def order_by_primary_key?
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keys.size == 1 && keys.first == primary_key
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end
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def primary_key
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relation.model.primary_key.to_sym
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end
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def sort_ascending?
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sort == :asc
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end
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# Build hash of request parameters for a given record (relevant to pagination)
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def params_for(record)
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return {} unless record
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keys.each_with_object({}) do |key, h|
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h["ks_prev_#{key}".to_sym] = record.attributes[key.to_s]
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end
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end
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private
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# All values present in request parameters that correspond to #keys.
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def values
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@values ||= keys.map do |key|
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request_context.params["ks_prev_#{key}".to_sym]
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end
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end
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# All keys relevant to pagination.
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# This always includes the primary key. Optionally, the `order_by` key is prepended.
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def keys
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@keys ||= [column_for_order_by(relation), primary_key].compact.uniq
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end
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end
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class KeysetPaginationStrategy
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attr_reader :request_context
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delegate :params, :header, :request, to: :request_context
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def initialize(request_context)
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@request_context = request_context
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end
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def paginate(relation)
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pagination = KeysetPaginationInfo.new(relation, request_context)
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paged_relation = relation.limit(per_page)
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if conds = conditions(pagination)
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paged_relation = paged_relation.where(*conds)
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end
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# In all cases: sort by primary key (possibly in addition to another sort column)
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paged_relation = paged_relation.order(pagination.primary_key => pagination.sort)
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add_default_pagination_headers
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if last_record = paged_relation.last
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next_page_params = pagination.params_for(last_record)
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add_navigation_links(next_page_params)
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end
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paged_relation
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end
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private
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def conditions(pagination)
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fields = pagination.fields
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return nil if fields.empty?
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placeholder = fields.map { '?' }
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comp = if pagination.sort_ascending?
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'>'
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else
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'<'
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end
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[
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# Row value comparison:
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# (A, B) < (a, b) <=> (A < a) OR (A = a AND B < b)
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# <=> A <= a AND ((A < a) OR (A = a AND B < b))
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"(#{fields.keys.join(',')}) #{comp} (#{placeholder.join(',')})",
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*fields.values
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]
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end
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def per_page
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params[:per_page]
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end
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def add_default_pagination_headers
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header 'X-Per-Page', per_page.to_s
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end
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def add_navigation_links(next_page_params)
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header 'X-Next-Page', page_href(next_page_params)
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header 'Link', link_for('next', next_page_params)
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end
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def page_href(next_page_params)
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request_url = request.url.split('?').first
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request_params = params.dup
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request_params[:per_page] = per_page
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request_params.merge!(next_page_params) if next_page_params
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"#{request_url}?#{request_params.to_query}"
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end
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def link_for(rel, next_page_params)
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%(<#{page_href(next_page_params)}>; rel="#{rel}")
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end
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end
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class DefaultPaginationStrategy
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attr_reader :ctx
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delegate :params, :header, :request, to: :ctx
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attr_reader :request_context
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delegate :params, :header, :request, to: :request_context
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def initialize(ctx)
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@ctx = ctx
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def initialize(request_context)
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@request_context = request_context
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end
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def paginate(relation)
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@ -7,7 +7,203 @@ describe API::Helpers::Pagination do
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Class.new.include(described_class).new
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end
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describe '#paginate' do
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describe '#paginate (keyset pagination)' do
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let(:value) { spy('return value') }
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before do
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allow(value).to receive(:to_query).and_return(value)
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allow(subject).to receive(:header).and_return(value)
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allow(subject).to receive(:params).and_return(value)
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allow(subject).to receive(:request).and_return(value)
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end
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context 'when resource can be paginated' do
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let!(:projects) do
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[
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create(:project, name: 'One'),
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create(:project, name: 'Two'),
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create(:project, name: 'Three')
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].sort_by { |e| -e.id } # sort by id desc (this is the default sort order for the API)
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end
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describe 'first page' do
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before do
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allow(subject).to receive(:params)
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.and_return({ pagination: 'keyset', per_page: 2 })
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end
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it 'returns appropriate amount of resources' do
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expect(subject.paginate(resource).count).to eq 2
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end
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it 'returns the first two records (by id desc)' do
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expect(subject.paginate(resource)).to eq(projects[0..1])
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end
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it 'adds appropriate headers' do
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expect_header('X-Per-Page', '2')
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expect_header('X-Next-Page', "#{value}?ks_prev_id=#{projects[1].id}&pagination=keyset&per_page=2")
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expect_header('Link', anything) do |_key, val|
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expect(val).to include('rel="next"')
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end
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subject.paginate(resource)
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end
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end
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describe 'second page' do
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before do
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allow(subject).to receive(:params)
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.and_return({ pagination: 'keyset', per_page: 2, ks_prev_id: projects[1].id })
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end
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it 'returns appropriate amount of resources' do
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expect(subject.paginate(resource).count).to eq 1
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end
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it 'returns the third record' do
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expect(subject.paginate(resource)).to eq(projects[2..2])
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end
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it 'adds appropriate headers' do
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expect_header('X-Per-Page', '2')
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expect_header('X-Next-Page', "#{value}?ks_prev_id=#{projects[2].id}&pagination=keyset&per_page=2")
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expect_header('Link', anything) do |_key, val|
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expect(val).to include('rel="next"')
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end
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subject.paginate(resource)
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end
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end
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describe 'third page' do
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before do
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allow(subject).to receive(:params)
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.and_return({ pagination: 'keyset', per_page: 2, ks_prev_id: projects[2].id })
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end
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it 'returns appropriate amount of resources' do
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expect(subject.paginate(resource).count).to eq 0
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end
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it 'adds appropriate headers' do
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expect_header('X-Per-Page', '2')
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expect(subject).not_to receive(:header).with('Link')
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subject.paginate(resource)
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end
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end
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context 'if order' do
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context 'is not present' do
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before do
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allow(subject).to receive(:params)
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.and_return({ pagination: 'keyset', per_page: 2 })
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end
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it 'is not present it adds default order(:id) desc' do
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resource.order_values = []
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paginated_relation = subject.paginate(resource)
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expect(resource.order_values).to be_empty
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expect(paginated_relation.order_values).to be_present
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expect(paginated_relation.order_values.size).to eq(1)
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expect(paginated_relation.order_values.first).to be_descending
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expect(paginated_relation.order_values.first.expr.name).to eq :id
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end
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end
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context 'is present' do
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let(:resource) { Project.all.order(name: :desc) }
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let!(:projects) do
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[
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create(:project, name: 'One'),
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create(:project, name: 'Two'),
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create(:project, name: 'Three'),
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create(:project, name: 'Three'), # Note the duplicate name
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create(:project, name: 'Four'),
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create(:project, name: 'Five'),
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create(:project, name: 'Six')
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]
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# if we sort this by name descending, id descending, this yields:
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# {
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# 2 => "Two",
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# 4 => "Three",
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# 3 => "Three",
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# 7 => "Six",
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# 1 => "One",
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# 5 => "Four",
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# 6 => "Five"
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# }
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#
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# (key is the id)
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end
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it 'it also orders by primary key' do
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allow(subject).to receive(:params)
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.and_return({ pagination: 'keyset', per_page: 2 })
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paginated_relation = subject.paginate(resource)
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expect(paginated_relation.order_values).to be_present
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expect(paginated_relation.order_values.size).to eq(2)
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expect(paginated_relation.order_values.first).to be_descending
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expect(paginated_relation.order_values.first.expr.name).to eq :name
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expect(paginated_relation.order_values.second).to be_descending
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expect(paginated_relation.order_values.second.expr.name).to eq :id
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end
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it 'it returns the right records (first page)' do
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allow(subject).to receive(:params)
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.and_return({ pagination: 'keyset', per_page: 2 })
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result = subject.paginate(resource)
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expect(result.first).to eq(projects[1])
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expect(result.second).to eq(projects[3])
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end
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it 'it returns the right records (second page)' do
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allow(subject).to receive(:params)
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.and_return({ pagination: 'keyset', ks_prev_id: projects[3].id, ks_prev_name: projects[3].name, per_page: 2 })
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result = subject.paginate(resource)
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expect(result.first).to eq(projects[2])
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expect(result.second).to eq(projects[6])
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end
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it 'it returns the right records (third page), note increased per_page' do
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allow(subject).to receive(:params)
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.and_return({ pagination: 'keyset', ks_prev_id: projects[6].id, ks_prev_name: projects[6].name, per_page: 5 })
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result = subject.paginate(resource)
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expect(result.size).to eq(3)
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expect(result.first).to eq(projects[0])
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expect(result.second).to eq(projects[4])
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expect(result.last).to eq(projects[5])
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end
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it 'it returns the right link to the next page' do
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allow(subject).to receive(:params)
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.and_return({ pagination: 'keyset', ks_prev_id: projects[3].id, ks_prev_name: projects[3].name, per_page: 2 })
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expect_header('X-Per-Page', '2')
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expect_header('X-Next-Page', "#{value}?ks_prev_id=#{projects[6].id}&ks_prev_name=#{projects[6].name}&pagination=keyset&per_page=2")
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expect_header('Link', anything) do |_key, val|
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expect(val).to include('rel="next"')
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end
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subject.paginate(resource)
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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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describe '#paginate (default offset-based pagination)' do
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let(:value) { spy('return value') }
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before do
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@ -146,14 +342,14 @@ describe API::Helpers::Pagination do
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end
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end
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end
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end
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def expect_header(*args, &block)
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expect(subject).to receive(:header).with(*args, &block)
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end
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def expect_header(*args, &block)
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expect(subject).to receive(:header).with(*args, &block)
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end
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def expect_message(method)
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expect(subject).to receive(method)
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.at_least(:once).and_return(value)
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end
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def expect_message(method)
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expect(subject).to receive(method)
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.at_least(:once).and_return(value)
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end
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end
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