Use pg_index's indnatts when indnkeyatts is not available

Using NULL when this column is not available does not work with old PostgreSQL (tested on version 9.6, as reported in #12600).

Instead, use `indnatts` which should be equal to what `indnkeyatts` would be as there is no "included attributes" in the index on these old versions (but only "key columns").

From https://www.postgresql.org/docs/17/catalog-pg-index.html:
* `indnatts`, "The total number of columns in the index [...]; this number includes both key and included attributes"
* `indnkeyatts`, "The number of key columns in the index, not counting any included columns [...]"

Fixes #12600.

Closes: #12611
Pull-request: https://github.com/sqlalchemy/sqlalchemy/pull/12611
Pull-request-sha: 8ff48a6225ec58fdfa84aec75d487238281b1ac1

Change-Id: Idcadcd7db545bc1f73d85b29347c8ba388b1b41d
(cherry picked from commit 9071811de76dea558f932215870e4a5513b30362)

diff --git a/doc/build/changelog/unreleased_20/12600.rst b/doc/build/changelog/unreleased_20/12600.rst
new file mode 100644 (file)
index 0000000..d544a22
--- /dev/null
+++ b/doc/build/changelog/unreleased_20/12600.rst
@@ -0,0 +1,7 @@
+.. change::
+    :tags: bug, postgresql, reflection
+    :tickets: 12600
+
+    Fixed regression caused by :ticket:`10665` where the newly modified
+    constraint reflection query would fail on older versions of PostgreSQL 
+    such as version 9.6.  Pull request courtesy Denis Laxalde.

diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index 9d4257cf0e480e82580bbb042badeac4c8c7bef7..69b78bb138a91968eaa100632028f2f03dac007c 100644 (file)
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -4104,7 +4104,7 @@ class PGDialect(default.DefaultDialect):
         if self.server_version_info >= (11, 0):
             indnkeyatts = pg_catalog.pg_index.c.indnkeyatts
         else:
-            indnkeyatts = sql.null().label("indnkeyatts")
+            indnkeyatts = pg_catalog.pg_index.c.indnatts.label("indnkeyatts")
 
         if self.server_version_info >= (15,):
             indnullsnotdistinct = pg_catalog.pg_index.c.indnullsnotdistinct
@@ -4224,10 +4224,7 @@ class PGDialect(default.DefaultDialect):
                         # See note in get_multi_indexes
                         all_cols = row["cols"]
                         indnkeyatts = row["indnkeyatts"]
-                        if (
-                            indnkeyatts is not None
-                            and len(all_cols) > indnkeyatts
-                        ):
+                        if len(all_cols) > indnkeyatts:
                             inc_cols = all_cols[indnkeyatts:]
                             cst_cols = all_cols[:indnkeyatts]
                         else:
@@ -4579,7 +4576,7 @@ class PGDialect(default.DefaultDialect):
         if self.server_version_info >= (11, 0):
             indnkeyatts = pg_catalog.pg_index.c.indnkeyatts
         else:
-            indnkeyatts = sql.null().label("indnkeyatts")
+            indnkeyatts = pg_catalog.pg_index.c.indnatts.label("indnkeyatts")
 
         if self.server_version_info >= (15,):
             nulls_not_distinct = pg_catalog.pg_index.c.indnullsnotdistinct
@@ -4689,10 +4686,7 @@ class PGDialect(default.DefaultDialect):
                     # "The number of key columns in the index, not counting any
                     # included columns, which are merely stored and do not
                     # participate in the index semantics"
-                    if (
-                        indnkeyatts is not None
-                        and len(all_elements) > indnkeyatts
-                    ):
+                    if len(all_elements) > indnkeyatts:
                         # this is a "covering index" which has INCLUDE columns
                         # as well as regular index columns
                         inc_cols = all_elements[indnkeyatts:]