Add method to discover required columns or all of them if it's a default aggregation

lib/cartodb/models/aggregation/aggregation-mapconfig.js

@@ -9,6 +9,8 @@ const {
 
 const SubstitutionTokens = require('../../utils/substitution-tokens');
 
+const removeDuplicates = arr => [...new Set(arr)];
+
 function prepareSql(sql) {
     return sql && SubstitutionTokens.replace(sql, {
         bbox: 'ST_MakeEnvelope(0,0,0,0)',
@@ -125,6 +127,43 @@ module.exports = class AggregationMapConfig extends MapConfig {
         return aggregation;
     }
 
+    getLayerAggregationColumns (index, callback) {
+        if (this._isDefaultLayerAggregation(index)) {
+            const skipGeoms = true;
+            return this.getLayerColumns(index, skipGeoms, (err, columns) => {
+                if (err) {
+                    return callback(err);
+                }
+
+                return callback(null, columns);
+            });
+        }
+
+        const columns = this._getLayerAggregationRequiredColumns(index);
+
+        return callback(null, columns);
+    }
+
+    _getLayerAggregationRequiredColumns (index) {
+        const { columns, dimensions } = this.getAggregation(index);
+
+        let aggregatedColumns = [];
+        if (columns) {
+            aggregatedColumns = Object.keys(columns)
+                .map(key => columns[key].aggregated_column)
+                .filter(aggregatedColumn => typeof aggregatedColumn === 'string');
+        }
+
+        let dimensionsColumns = [];
+        if (dimensions) {
+            dimensionsColumns = Object.keys(dimensions)
+                .map(key => dimensions[key])
+                .filter(dimension => typeof dimension === 'string');
+        }
+
+        return removeDuplicates(aggregatedColumns.concat(dimensionsColumns));
+    }
+
     doesLayerReachThreshold(index, featureCount) {
         const threshold = this.getAggregation(index) && this.getAggregation(index).threshold ?
             this.getAggregation(index).threshold :
@@ -165,7 +204,7 @@ module.exports = class AggregationMapConfig extends MapConfig {
         });
     }
 
-    isDefaultLayerAggregation (index) {
+    _isDefaultLayerAggregation (index) {
         const aggregation = this.getAggregation(index);
 
         return (this.isVectorOnlyMapConfig() && !this.hasLayerAggregation(index)) ||