#434

backend/app/services/counts_pivot_totals.rb

@@ -0,0 +1,59 @@
+# Re-aggregate the population, never add up already grouped cells (multi-value axes overlap).
+class CountsPivotTotals
+  def initialize(population, axes, row_headers, column_headers)
+    @population = population
+    @axes = axes
+    @rows = row_headers.group_by { _1[:values].length }
+    @columns = column_headers.group_by { _1[:values].length }
+  end
+
+  def call
+    queries = @rows.flat_map do |row_depth, headers|
+      @columns.filter_map do |column_depth, columns|
+        next if row_depth == @axes.rows.length && column_depth == @axes.columns.length
+
+        indexes = (0...row_depth).to_a +
+            (0...column_depth).map { @axes.rows.length + _1 }
+        expressions = indexes.map { @axes.expressions[_1] }
+        scope = @population.scope.except(:select, :order)
+        joins = @axes.joins(indexes.map { @axes.all[_1].fetch('field') })
+        scope = scope.joins(joins) unless joins.empty?
+        if row_depth.positive?
+          tuples = headers.map { _1[:values] }.uniq
+          predicate = tuples.map { Array.new(row_depth) { |i|
+            "(#{ expressions[i] }) <=> ?"
+          }.join(' AND ') }.map { "(#{ _1 })" }.join(' OR ')
+          scope = scope.where(predicate, *tuples.flatten)
+        end
+        if column_depth.positive?
+          tuples = columns.map { _1[:values] }.uniq
+          predicate = tuples.map { Array.new(column_depth) { |i|
+            "(#{ expressions[row_depth + i] }) <=> ?"
+          }.join(' AND ') }.map { "(#{ _1 })" }.join(' OR ')
+          scope = scope.where(predicate, *tuples.flatten)
+        end
+        grouped = expressions.each_with_index.map { |expression, index|
+          "#{ expression } AS v#{ index }"
+        }
+        # Fixed-width result coordinates, independent of NULL and of translated labels.
+        padding = (expressions.length...@axes.all.length).map { "NULL AS v#{ _1 }" }
+        fields = ["#{ row_depth } AS row_depth", "#{ column_depth } AS column_depth"] +
+            grouped + padding + ['COUNT(DISTINCT v.id) AS count']
+        scope = scope.group(*expressions.map { Arel.sql(_1) }) if expressions.any?
+        scope.optimizer_hints('MAX_EXECUTION_TIME(10000)')
+            .select(Arel.sql(fields.join(', '))).to_sql
+      end
+    end
+    return [] if queries.empty?
+
+    sql = queries.map { "(#{ _1 })" }.join(' UNION ALL ')
+    @population.definition.model.connection.select_all(
+        "SELECT /*+ MAX_EXECUTION_TIME(10000) */ * FROM (#{ sql }) totals").map do |record|
+      row_depth = record['row_depth'].to_i
+      column_depth = record['column_depth'].to_i
+      { row: (0...row_depth).map { record["v#{ _1 }"] },
+        column: (0...column_depth).map { record["v#{ row_depth + _1 }"] },
+        count: record['count'].to_i }
+    end
+  end
+end