- calling str() on a core sql construct has been made more "friendly",

when the construct contains non-standard sql elements such as
returning, array index operations, or dialect-specific or custom
datatypes.  a string is now returned in these cases rendering an
approximation of the construct (typically the postgresql-style
version of it) rather than raising an error. fixes #3631
- add within_group to top-level imports
- add eq_ignore_whitespace to sqlalchemy.testing imports

6 files changed, 56 insertions, 2 deletions

diff --git a/lib/sqlalchemy/__init__.py b/lib/sqlalchemy/__init__.py
index 40b8000e8..dde179bf5 100644
--- a/lib/sqlalchemy/__init__.py
+++ b/lib/sqlalchemy/__init__.py
@@ -51,6 +51,7 @@ from .sql import (
     union,
     union_all,
     update,
+    within_group,
     )
 
 from .types import (
diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py
index 3e5f339b1..9f845e79d 100644
--- a/lib/sqlalchemy/engine/default.py
+++ b/lib/sqlalchemy/engine/default.py
@@ -474,6 +474,23 @@ class DefaultDialect(interfaces.Dialect):
         self.set_isolation_level(dbapi_conn, self.default_isolation_level)
 
 
+class StrCompileDialect(DefaultDialect):
+
+    statement_compiler = compiler.StrSQLCompiler
+    ddl_compiler = compiler.DDLCompiler
+    type_compiler = compiler.StrSQLTypeCompiler
+    preparer = compiler.IdentifierPreparer
+
+    supports_sequences = True
+    sequences_optional = True
+    preexecute_autoincrement_sequences = False
+    implicit_returning = False
+
+    supports_native_boolean = True
+
+    supports_simple_order_by_label = True
+
+
 class DefaultExecutionContext(interfaces.ExecutionContext):
     isinsert = False
     isupdate = False
diff --git a/lib/sqlalchemy/sql/__init__.py b/lib/sqlalchemy/sql/__init__.py
index fa2cf2399..f4ad3ec00 100644
--- a/lib/sqlalchemy/sql/__init__.py
+++ b/lib/sqlalchemy/sql/__init__.py
@@ -66,6 +66,7 @@ from .expression import (
     union,
     union_all,
     update,
+    within_group
 )
 
 from .visitors import ClauseVisitor
diff --git a/lib/sqlalchemy/sql/compiler.py b/lib/sqlalchemy/sql/compiler.py
index c5f87cc33..076ae53b2 100644
--- a/lib/sqlalchemy/sql/compiler.py
+++ b/lib/sqlalchemy/sql/compiler.py
@@ -2118,6 +2118,30 @@ class SQLCompiler(Compiled):
             self.preparer.format_savepoint(savepoint_stmt)
 
 
+class StrSQLCompiler(SQLCompiler):
+    """"a compiler subclass with a few non-standard SQL features allowed.
+
+    Used for stringification of SQL statements when a real dialect is not
+    available.
+
+    """
+
+    def visit_getitem_binary(self, binary, operator, **kw):
+        return "%s[%s]" % (
+            self.process(binary.left, **kw),
+            self.process(binary.right, **kw)
+        )
+
+    def returning_clause(self, stmt, returning_cols):
+
+        columns = [
+            self._label_select_column(None, c, True, False, {})
+            for c in elements._select_iterables(returning_cols)
+        ]
+
+        return 'RETURNING ' + ', '.join(columns)
+
+
 class DDLCompiler(Compiled):
 
     @util.memoized_property
@@ -2640,6 +2664,17 @@ class GenericTypeCompiler(TypeCompiler):
         return type_.get_col_spec(**kw)
 
 
+class StrSQLTypeCompiler(GenericTypeCompiler):
+    def __getattr__(self, key):
+        if key.startswith("visit_"):
+            return self._visit_unknown
+        else:
+            raise AttributeError(key)
+
+    def _visit_unknown(self, type_, **kw):
+        return "%s" % type_.__class__.__name__
+
+
 class IdentifierPreparer(object):
 
     """Handle quoting and case-folding of identifiers based on options."""
diff --git a/lib/sqlalchemy/sql/elements.py b/lib/sqlalchemy/sql/elements.py
index de17aabb3..fe2fecce8 100644
--- a/lib/sqlalchemy/sql/elements.py
+++ b/lib/sqlalchemy/sql/elements.py
@@ -429,7 +429,7 @@ class ClauseElement(Visitable):
                 dialect = self.bind.dialect
                 bind = self.bind
             else:
-                dialect = default.DefaultDialect()
+                dialect = default.StrCompileDialect()
         return self._compiler(dialect, bind=bind, **kw)
 
     def _compiler(self, dialect, **kw):
diff --git a/lib/sqlalchemy/testing/__init__.py b/lib/sqlalchemy/testing/__init__.py
index bd6377eb7..d24f31321 100644
--- a/lib/sqlalchemy/testing/__init__.py
+++ b/lib/sqlalchemy/testing/__init__.py
@@ -22,7 +22,7 @@ from .assertions import emits_warning, emits_warning_on, uses_deprecated, \
     eq_, ne_, le_, is_, is_not_, startswith_, assert_raises, \
     assert_raises_message, AssertsCompiledSQL, ComparesTables, \
     AssertsExecutionResults, expect_deprecated, expect_warnings, \
-    in_, not_in_
+    in_, not_in_, eq_ignore_whitespace
 
 from .util import run_as_contextmanager, rowset, fail, \
     provide_metadata, adict, force_drop_names, \