Use tufts admin_set predicate to query admin set membership

This commit fixes the admin dashboard display for the number of
items in an admin set. Unfortunately, although Hyrax aims to
make the admin set predicate configurable, it is hard coded in
many places.

We opened a ticket in Hyrax to address this:
samvera/hyrax#2405

app/services/hyrax/admin_set_service.rb

@@ -0,0 +1,70 @@
+# frozen_string_literal: true
+
+# Override AdminSetService so we can change the join_field from isPartOf_ssim
+# to admin_set_member_ssim. Eventually, all of these should reference
+# Hyrax.config.admin_set_predicate, and we have opened a ticket in Hyrax to
+# address that (See https://github.com/samvera/hyrax/issues/2405). In the meantime,
+# we have to hard-code the new value.
+module Hyrax
+  # Returns AdminSets that the current user has permission to use.
+  class AdminSetService
+    attr_reader :context, :search_builder
+    class_attribute :default_search_builder
+    self.default_search_builder = Hyrax::AdminSetSearchBuilder
+
+    # @param [#repository,#blacklight_config,#current_ability] context
+    def initialize(context, search_builder = default_search_builder)
+      @context = context
+      @search_builder = search_builder
+    end
+
+    # @param [Symbol] access :deposit, :read or :edit
+    def search_results(access)
+      response = context.repository.search(builder(access))
+      response.documents
+    end
+
+    SearchResultForWorkCount = Struct.new(:admin_set, :work_count, :file_count)
+
+    # This performs a two pass query, first getting the AdminSets
+    # and then getting the work and file counts
+    # @param [Symbol] access :read or :edit
+    # @param join_field [String] how are we joining the admin_set ids (by default "isPartOf_ssim")
+    # @return [Array<Hyrax::AdminSetService::SearchResultForWorkCount>] a list with document, then work and file count
+    def search_results_with_work_count(access, join_field: "admin_set_member_ssim")
+      admin_sets = search_results(access)
+      ids = admin_sets.map(&:id).join(',')
+      query = "{!terms f=#{join_field}}#{ids}"
+      results = ActiveFedora::SolrService.instance.conn.get(
+        ActiveFedora::SolrService.select_path,
+        params: { fq: query,
+                  'facet.field' => join_field }
+      )
+      counts = results['facet_counts']['facet_fields'][join_field].each_slice(2).to_h
+      file_counts = count_files(results)
+      admin_sets.map do |admin_set|
+        SearchResultForWorkCount.new(admin_set, counts[admin_set.id].to_i, file_counts[admin_set.id].to_i)
+      end
+    end
+
+    private
+
+      # @param [Symbol] access :read or :edit
+      def builder(access)
+        search_builder.new(context, access).rows(100)
+      end
+
+      # Count number of files from admin set works
+      # @param [Array] results Solr search result
+      # @return [Hash] admin set id keys and file count values
+      def count_files(results)
+        file_counts = Hash.new(0)
+        results['response']['docs'].each do |doc|
+          doc['admin_set_member_ssim'].each do |id|
+            file_counts[id] += doc.fetch('file_set_ids_ssim', []).length
+          end
+        end
+        file_counts
+      end
+  end
+end