fix: preserve $count for result of SELECT queries

db-service/lib/SQLService.js

@@ -79,7 +79,10 @@ class SQLService extends DatabaseService {
     let rows = await ps.all(values)
     if (rows.length)
       if (cqn.SELECT.expand) rows = rows.map(r => (typeof r._json_ === 'string' ? JSON.parse(r._json_) : r._json_ || r))
-    if (cqn.SELECT.count) rows.$count = await this.count(query, rows)
+    if (cqn.SELECT.count) {
+      // REVISIT: the runtime always expects that the count is preserved with .map, required for renaming in mocks
+      return SQLService._arrayWithCount(rows, await this.count(query, rows))
+    }
     return cqn.SELECT.one || query.SELECT.from?.ref?.[0].cardinality?.max === 1 ? rows[0] : rows
   }
 
@@ -252,6 +255,17 @@ class SQLService extends DatabaseService {
    */
   static CQN2SQL = require('./cqn2sql').class
 
+  // REVISIT: There must be a better way
+  // preserves $count for .map calls on array
+  static _arrayWithCount = function (a, count) {
+    const _map = a.map
+    const map = function (..._) { return SQLService._arrayWithCount(_map.call(a, ..._), count) }
+    return Object.defineProperties(a, {
+      $count: { value: count, enumerable: false, configurable: true, writable: true },
+      map: { value: map, enumerable: false, configurable: true, writable: true }
+    })
+  }
+
   /** @param {unknown[]} args */
   constructor(...args) {
     super(...args)
@@ -387,6 +401,7 @@ const _unquirked = q => {
   return q
 }
 
+
 const sqls = new class extends SQLService { get factory() { return null } }
 cds.extend(cds.ql.Query).with(
   class {

hana/lib/HANAService.js

@@ -83,7 +83,10 @@ class HANAService extends SQLService {
     if (rows.length) {
       rows = this.parseRows(rows)
     }
-    if (cqn.SELECT.count) rows.$count = await this.count(query, rows)
+    if (cqn.SELECT.count) {
+      // REVISIT: the runtime always expects that the count is preserved with .map, required for renaming in mocks
+      return HANAService._arrayWithCount(rows, await this.count(query, rows))
+    }
     return cqn.SELECT.one || query.SELECT.from.ref?.[0].cardinality?.max === 1 ? rows[0] || null : rows
   }
 

test/compliance/SELECT.test.js

@@ -299,8 +299,13 @@ describe('SELECT', () => {
   })
 
   describe('count', () => {
-    test.skip('missing', () => {
-      throw new Error('not supported')
+    test('count is preserved with .map', async () => {
+      const query = SELECT.from('complex.Authors')
+      query.SELECT.count = true
+      const result = await query
+      assert.strictEqual(result.$count, 1)
+      const renamed = result.map(row => ({key: row.ID, fullName: row.name}))
+      assert.strictEqual(renamed.$count, 1)
     })
   })