fix: rewrite assoc chains if intermediate assoc is not fk (#715)

in one case a ref `genre.parent.ID` was mistaken for a foreign key
access because `ID` is fk of `parent`. But because `parent` is not fk of
`genre`, it is actually not an fk access.
Hence, the reference actually needs to point to the correct join node.

db-service/lib/cqn4sql.js

@@ -1573,7 +1573,7 @@ function cqn4sql(originalQuery, model) {
           transformedFrom.args.push(f)
         }
       })
-      return { transformedFrom }
+      return { transformedFrom, transformedWhere: existingWhere }
     } else if (from.SELECT) {
       transformedFrom = transformSubquery(from)
       if (from.as) {
@@ -1583,7 +1583,7 @@ function cqn4sql(originalQuery, model) {
         // select from anonymous query, use artificial alias
         transformedFrom.as = Object.keys(originalQuery.sources)[0]
       }
-      return { transformedFrom }
+      return { transformedFrom, transformedWhere: existingWhere }
     } else {
       return _transformFrom()
     }

db-service/lib/infer/index.js

@@ -1013,9 +1013,11 @@ function infer(originalQuery, model) {
           }
           return true
         }
-        if (assoc && assoc.keys?.some(key => key.ref.every((step, j) => column.ref[i + j] === step))) {
+        if (assoc) {
           // foreign key access without filters never join relevant
-          return false
+          if (assoc.keys?.some(key => key.ref.every((step, j) => column.ref[i + j] === step))) return false
+          // <assoc>.<anotherAssoc>.<…> is join relevant as <anotherAssoc> is not fk of <assoc>
+          return true
         }
         if (link.definition.target && link.definition.keys) {
           if (column.ref[i + 1] || assoc) fkAccess = false
@@ -1198,6 +1200,8 @@ function infer(originalQuery, model) {
         firstStepIsEntity = true
         if (arg.$refLinks.length === 1) return `${cur.definition.name}`
         return `${cur.definition.name}`
+      } else if (cur.definition.SELECT) {
+        return `${cur.definition.as}`
       }
       const dot = i === 1 && firstStepIsEntity ? ':' : '.' // divide with colon if first step is entity
       return res !== '' ? res + dot + cur.definition.name : cur.definition.name

db-service/test/cds-infer/negative.test.js

@@ -53,6 +53,10 @@ describe('negative', () => {
       let query = CQL`SELECT from (select from bookshop.Books { ID as FooID }) as Foo { ID }`
       expect(() => _inferred(query)).to.throw(/"ID" not found in the elements of "Foo"/)
     })
+    it("reference in group by can't be found in alias of subquery", () => {
+      let query = CQL`SELECT from (select from bookshop.Books { ID as FooID }) as Foo group by Foo.ID`
+      expect(() => _inferred(query)).to.throw(/"ID" not found in "Foo"/)
+    })
 
     it('intermediate step in path expression is not found', () => {
       let query = CQL`SELECT from bookshop.Books as Foo { Foo.notExisting.sub.boz }`
@@ -397,11 +401,15 @@ describe('negative', () => {
     })
     it('rejects non fk traversal in infix filter in where exists', () => {
       let query = CQL`SELECT from bookshop.Books where exists author.books[author.name = 'John Doe']`
-      expect(() => _inferred(query)).to.throw(/Only foreign keys of “author” can be accessed in infix filter, but found “name”/,) // revisit: better error location ""bookshop.Books:author"
+      expect(() => _inferred(query)).to.throw(
+        /Only foreign keys of “author” can be accessed in infix filter, but found “name”/,
+      ) // revisit: better error location ""bookshop.Books:author"
     })
     it('rejects unmanaged traversal in infix filter in where exists', () => {
       let query = CQL`SELECT from bookshop.Books where exists author.books[coAuthorUnmanaged.name = 'John Doe']`
-      expect(() => _inferred(query)).to.throw(/Unexpected unmanaged association “coAuthorUnmanaged” in filter expression of “books”/,) // revisit: better error location ""bookshop.Books:author"
+      expect(() => _inferred(query)).to.throw(
+        /Unexpected unmanaged association “coAuthorUnmanaged” in filter expression of “books”/,
+      ) // revisit: better error location ""bookshop.Books:author"
     })
 
     it('rejects non fk traversal in infix filter in column', () => {

db-service/test/cqn4sql/assocs2joins.test.js

@@ -725,6 +725,26 @@ describe('Unfolding Association Path Expressions to Joins', () => {
       `)
   })
 
+  it('properly rewrite association chains if intermediate assoc is not fk', () => {
+    // this issue came up for ref: [genre.parent.ID] because "ID" is fk of "parent"
+    // but "parent" is not fk of "genre"
+    const q = CQL`SELECT from (select genre from bookshop.Books) as book {
+      genre { name }
+    } group by genre.parent.ID, genre.parent.name`
+    const qx = CQL`
+    SELECT from (select Books.genre_ID from bookshop.Books as Books) as book
+                                left join bookshop.Genres as genre on genre.ID = book.genre_ID
+                                left join bookshop.Genres as parent on parent.ID = genre.parent_ID
+    {
+      (SELECT
+          genre2.name
+        from bookshop.Genres as genre2
+        where book.genre_ID = genre2.ID) as genre
+    } group by parent.ID, parent.name`
+    const res = cqn4sql(q, model)
+    expect(JSON.parse(JSON.stringify(res))).to.deep.eql(qx)
+  })
+
   // some notes for later:
   //   what if only field we fetch from assoc target is virtual? -> make join, but don't fetch anything (?)
 })