- MySQL boolean symbols "true", "false" work again. 0.9's change

in :ticket:`2682` disallowed the MySQL dialect from making use of the
"true" and "false" symbols in the context of "IS" / "IS NOT", but
MySQL supports this syntax even though it has no boolean type.
MySQL remains "non native boolean", but the :func:`.true`
and :func:`.false` symbols again produce the
keywords "true" and "false", so that an expression like
``column.is_(true())`` again works on MySQL.
fixes #3186

1 files changed, 12 insertions, 0 deletions

diff --git a/lib/sqlalchemy/dialects/mysql/base.py b/lib/sqlalchemy/dialects/mysql/base.py
index 4dccd2760..247b7a143 100644
--- a/lib/sqlalchemy/dialects/mysql/base.py
+++ b/lib/sqlalchemy/dialects/mysql/base.py
@@ -1637,6 +1637,14 @@ class MySQLCompiler(compiler.SQLCompiler):
             value = value.replace('\\', '\\\\')
         return value
 
+    # override native_boolean=False behavior here, as
+    # MySQL still supports native boolean
+    def visit_true(self, element, **kw):
+        return "true"
+
+    def visit_false(self, element, **kw):
+        return "false"
+
     def get_select_precolumns(self, select):
         """Add special MySQL keywords in place of DISTINCT.
 
@@ -2215,6 +2223,10 @@ class MySQLDialect(default.DefaultDialect):
     name = 'mysql'
     supports_alter = True
 
+    # MySQL has no true "boolean" type; we
+    # allow for the "true" and "false" keywords, however
+    supports_native_boolean = False
+
     # identifiers are 64, however aliases can be 255...
     max_identifier_length = 255
     max_index_name_length = 64