Add Sequence to StrSQLCompiler

Added :class:`.Sequence` to the "string SQL" system that will render a
meaningful string expression (``"<next sequence value: my_sequence>"``)
when stringifying without a dialect a statement that includes a "sequence
nextvalue" expression, rather than raising a compilation error.

Fixes: #4144
Change-Id: Ia910f0e22008a7cde7597365954ede324101cf4d

1 files changed, 12 insertions, 0 deletions

diff --git a/test/sql/test_compiler.py b/test/sql/test_compiler.py
index 993008c07..22b46cc46 100644
--- a/test/sql/test_compiler.py
+++ b/test/sql/test_compiler.py
@@ -2898,6 +2898,18 @@ class StringifySpecialTest(fixtures.TestBase):
             "SELECT anon_1.myid FROM anon_1"
         )
 
+    def test_next_sequence_value(self):
+        # using descriptive text that is intentionally not compatible
+        # with any particular backend, since all backends have different
+        # syntax
+
+        seq = Sequence("my_sequence")
+
+        eq_ignore_whitespace(
+            str(seq.next_value()),
+            "<next sequence value: my_sequence>"
+        )
+
     def test_returning(self):
         stmt = table1.insert().returning(table1.c.myid)