Description

In CDL, inline and expand operators use the { } syntax to nest sub-elements in a select clause. In CDS compiler v7 (CDS 10), using these operators in SQL-style as select view definitions (in the part before the from keyword) is a hard error. The inline and expand operators remain valid in CQL projection-style views (as projection on) and in query builder code. SQL-style views that use { } before from must be rewritten either as projection-style views or by flattening the nested element access.

How to Check

• [ ] Run cds compile — the compiler emits a hard error for each affected SQL-style view.
• [ ] Search all .cds files for as select to find SQL-style view definitions.
• [ ] For each match, inspect the select clause for { before the from keyword — indicating inline or expand usage.

Migration Steps

1. Locate a SQL-style view using inline or expand in the select list:

   // Breaking: inline operator in SQL-style select
   entity BookDetails as select from Books {
     ID,
     author { name, bio },
     title
   };

2. Convert to a projection-style view, which fully supports inline/expand:

   - entity BookDetails as select from Books {
   -   ID,
   -   author { name, bio },
   -   title
   - };
   + entity BookDetails as projection on Books {
   +   ID,
   +   author { name, bio },
   +   title
   + };

3. If the SQL-style select is needed for its filtering or join capabilities, flatten the inline expression by using explicit path references instead:

   - entity BookDetails as select from Books {
   -   ID,
   -   author { name }
   - } where stock > 0;
   + entity BookDetails as select from Books
   +   left join Authors on Books.author_ID = Authors.ID
   + {
   +   Books.ID,
   +   Authors.name as authorName
   + } where Books.stock > 0;

Examples

SQL-style select with inline operator — breaking:

// Breaking: inline/expand used in SQL-style select (before FROM)
entity BooksWithAuthor as select from Books {
  ID, title,
  author { name, dateOfBirth }  // ← inline operator before FROM: error
};

CQL-style projection with inline operator — valid, no change needed:

// Valid: inline operator after FROM in CQL-style
entity BooksWithAuthor as projection on Books {
  ID, title,
  author { name, dateOfBirth }  // ← same operator, CQL-style: fine
};

To migrate, change as select from to as projection on:

- entity BooksWithAuthor as select from Books {
+ entity BooksWithAuthor as projection on Books {
    ID, title,
    author { name, dateOfBirth }
  };

Notes

Projection-style views (as projection on) should be preferred over SQL-style views (as select from) in CDL when inline/expand operators are needed. SQL-style views are intended for cases requiring explicit joins, grouping, or subqueries that projection syntax cannot express. For views that only add nesting to a single base entity, switching to as projection on is a straightforward migration with no semantic change.