fix: prepend aliases to refs within function args in on conditions

 we need to drill recursively into the function arguments found in
on-conditions and prepend aliases of the outer query in case of scoped
queries / expands

fixes #779

db-service/lib/cqn4sql.js

@@ -1852,6 +1852,11 @@ function cqn4sql(originalQuery, model) {
           result[i] = asXpr(xpr)
           continue
         }
+        if(lhs.args) {
+          const args = calculateOnCondition(lhs.args)
+          result[i] = { ...lhs, args }
+          continue
+        }
         const rhs = result[i + 2]
         if (rhs?.ref || lhs.ref) {
           // if we have refs on each side of the comparison, we might need to perform tuple expansion

db-service/test/bookshop/db/schema.cds

@@ -422,3 +422,10 @@ entity Item {
   key ID: Integer;
   item: Association to Item;
 }
+
+entity Posts {
+  key ID: Integer;
+  name: String;
+  iSimilar: Association to many Posts on UPPER(name) = UPPER(iSimilar.name);
+  iSimilarNested: Association to many Posts on UPPER(iSimilarNested.name) = UPPER(LOWER(UPPER(name)), name); 
+}

db-service/test/cqn4sql/table-alias.test.js

@@ -263,6 +263,49 @@ describe('table alias access', () => {
       let result = cqn4sql(query, model)
       expect(result).to.deep.equal(expected)
     })
+
+    it('refs in function args in on condition are aliased', () => {
+      let query = CQL`
+        SELECT
+          ID,
+          iSimilar { name }
+        from bookshop.Posts`
+
+      const expected = CQL`
+        SELECT
+          Posts.ID,
+          (
+            SELECT from bookshop.Posts as iSimilar {
+              iSimilar.name
+            }
+            where UPPER(Posts.name) = UPPER(iSimilar.name)
+          ) as iSimilar
+        from bookshop.Posts as Posts`
+
+      let result = cqn4sql(query, model)
+      expect(JSON.parse(JSON.stringify(result))).to.deep.equal(expected)
+    })
+    it('refs in nested function args in on condition are aliased', () => {
+      let query = CQL`
+        SELECT
+          ID,
+          iSimilarNested { name }
+        from bookshop.Posts`
+
+      const expected = CQL`
+        SELECT
+          Posts.ID,
+          (
+            SELECT from bookshop.Posts as iSimilarNested {
+              iSimilarNested.name
+            }
+            where UPPER(iSimilarNested.name) = UPPER(LOWER(UPPER(Posts.name)), Posts.name)
+          ) as iSimilarNested
+        from bookshop.Posts as Posts`
+
+      let result = cqn4sql(query, model)
+      expect(JSON.parse(JSON.stringify(result))).to.deep.equal(expected)
+    })
   })
 
   describe('replace $self references', () => {