Add feature: duplicate/expression columns

1 files changed, 19 insertions, 0 deletions

diff --git a/feature/list b/feature/list
index dff0004..f2043e0 100644
--- a/feature/list
+++ b/feature/list
@@ -23,3 +23,22 @@
   Got two questions on the mailing list about that in one week. Maybe
   always diagnose lack of public ctor? Maybe with a warning if no
   relationship? The no_ctor pragma like no_id?
+
+? Duplicate columns
+
+  It can sometimes be useful to map multiple data members to the same
+  column. For example, to map a shared_ptr to another object via id.
+  Or to update object id.
+
+  To implement this, we will have to be able to ignore duplicates in
+  the INSERT statement and in generated schema. So there will have to
+  be quite a bit of work throughout (bind, init, column counts, etc).
+
+  Also not clear if it is a good idea to always ignore duplicates
+  (could actually be a mistake) or only if the column name is
+  specified explicitly (still can be a mistake). Or mark it as a
+  duplicate with a special pragma.
+
+  Is this a special case of something like "expression columns"? It
+  seems the only place where such a duplicate column will actually
+  be mentioned is the SELECT statement.