Use pg_get_constraintdef for CHECK constraint reflection

Revised the query used when reflecting CHECK constraints to make use of the
``pg_get_constraintdef`` function, as the ``consrc`` column is being
deprecated in PG 12.  Thanks to John A Stevenson for the tip.

Fixes: #4463
Change-Id: Ie0ee9bdfddb0635db72b35c2e2e4b27f154162fd

1 files changed, 13 insertions, 2 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index ecdbe0018..e9040fb43 100644
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -3381,7 +3381,7 @@ class PGDialect(default.DefaultDialect):
         CHECK_SQL = """
             SELECT
                 cons.conname as name,
-                cons.consrc as src
+                pg_get_constraintdef(cons.oid) as src
             FROM
                 pg_catalog.pg_constraint cons
             WHERE
@@ -3391,8 +3391,19 @@ class PGDialect(default.DefaultDialect):
 
         c = connection.execute(sql.text(CHECK_SQL), table_oid=table_oid)
 
+        # samples:
+        # "CHECK (((a > 1) AND (a < 5)))"
+        # "CHECK (((a = 1) OR ((a > 2) AND (a < 5))))"
+        def match_cons(src):
+            m = re.match(r"^CHECK *\(\((.+)\)\)$", src)
+            if not m:
+                util.warn("Could not parse CHECK constraint text: %r" % src)
+                return ""
+            return m.group(1)
+
         return [
-            {"name": name, "sqltext": src[1:-1]} for name, src in c.fetchall()
+            {"name": name, "sqltext": match_cons(src)}
+            for name, src in c.fetchall()
         ]
 
     def _load_enums(self, connection, schema=None):