fix: tree table with expand (#1363)

The foreign key in the case of an expand was not included in the inner
SELECT which resulted in the error "no such column".

Author: larsplessing

db-service/lib/cqn2sql.js

@@ -350,7 +350,13 @@ class CQN2SQLRenderer {
       if (element['@Core.Computed'] && name in availableComputedColumns) continue
       if (name.toUpperCase() in reservedColumnNames) ref.as = `$$${name}$$`
       columnsIn.push(ref)
-      if (from.args || columnsFiltered.find(c => this.column_name(c) === name)) {
+      const foreignkey4 = element._foreignKey4
+      if (
+        from.args ||
+        columnsFiltered.find(c => this.column_name(c) === name) ||
+        // foreignkey needs to be included when the association is expanded
+        (foreignkey4 && q.SELECT.columns.some(c => c.element?.isAssociation && c.element.name === foreignkey4))
+      ) {
         columnsOut.push(ref.as ? { ref: [ref.as], as: name } : ref)
       }
     }

test/scenarios/bookshop/hierarchy.test.js

@@ -32,6 +32,15 @@ describe('Bookshop - Genres', () => {
     await GET(`/tree/Genres?$select=DrillState,ID,name&$apply=${topLevels}(HierarchyNodes=$root/GenreHierarchy,HierarchyQualifier='GenreHierarchy',NodeProperty='ID')`)
   })
 
+  test('TopLevels with $expand', async () => {
+    const query = `/tree/Genres?$select=DrillState,ID,name&$apply=${topLevels}(HierarchyNodes=$root/GenreHierarchy,HierarchyQualifier='GenreHierarchy',NodeProperty='ID',Levels=2)&$select=DrillState,ID,name&$expand=parent($select=ID,name)`
+    const res = await GET(query)
+
+    // should have parent expanded
+    const hasParent = res.data.value.some(item => item.parent)
+    expect(hasParent).to.be.true
+  })
+
   test('ancestors($filter)/TopLevels(1)', async () => {
     const res = await GET(`/tree/Genres?$select=DrillState,ID,name&$apply=ancestors($root/GenreHierarchy,GenreHierarchy,ID,filter(tolower(name) eq tolower('Fantasy')),keep start)/${topLevels}(HierarchyNodes=$root/GenreHierarchy,HierarchyQualifier='GenreHierarchy',NodeProperty='ID',Levels=1)`)
     expect(res).property('data').property('value').deep.eq([