sql.Identifier can wrap a sequence of strings to represent qualified names

Close #732.

NEWS

@@ -7,6 +7,8 @@ What's new in psycopg 2.8
 New features:
 
 - Added `~psycopg2.extensions.encrypt_password()` function (:ticket:`#576`).
+- `~psycopg2.sql.Identifier` can represent qualified names in SQL composition
+  (:ticket:`#732`).
 - `!str()` on `~psycopg2.extras.Range` produces a human-readable representation
   (:ticket:`#773`).
 - `~psycopg2.extras.DictCursor` and `~psycopg2.extras.RealDictCursor` rows

doc/src/sql.rst

@@ -77,16 +77,26 @@ to cursor methods such as `~cursor.execute()`, `~cursor.executemany()`,
 
 .. autoclass:: Identifier
 
-    .. autoattribute:: string
+    .. versionchanged:: 2.8
+        added support for multiple strings.
+
+    .. autoattribute:: strings
+
+        .. versionadded:: 2.8
+            previous verions only had a `!string` attribute. The attribute
+            still exists but is deprecate and will only work if the
+            `!Identifier` wraps a single string.
 
 .. autoclass:: Literal
 
     .. autoattribute:: wrapped
 
+
 .. autoclass:: Placeholder
 
     .. autoattribute:: name
 
+
 .. autoclass:: Composed
 
     .. autoattribute:: seq

lib/sql.py

@@ -290,7 +290,7 @@ class SQL(Composable):
 
 class Identifier(Composable):
     """
-    A `Composable` representing an SQL identifer.
+    A `Composable` representing an SQL identifer or a dot-separated sequence.
 
     Identifiers usually represent names of database objects, such as tables or
     fields. PostgreSQL identifiers follow `different rules`__ than SQL string
@@ -307,20 +307,50 @@ class Identifier(Composable):
         >>> print(sql.SQL(', ').join([t1, t2, t3]).as_string(conn))
         "foo", "ba'r", "ba""z"
 
-    """
-    def __init__(self, string):
-        if not isinstance(string, string_types):
-            raise TypeError("SQL identifiers must be strings")
+    Multiple strings can be passed to the object to represent a qualified name,
+    i.e. a dot-separated sequence of identifiers.
 
-        super(Identifier, self).__init__(string)
+    Example::
+
+        >>> query = sql.SQL("select {} from {}").format(
+        ...     sql.Identifier("table", "field"),
+        ...     sql.Identifier("schema", "table"))
+        >>> print(query.as_string(conn))
+        select "table"."field" from "schema"."table"
+
+    """
+    def __init__(self, *strings):
+        if not strings:
+            raise TypeError("Identifier cannot be empty")
+
+        for s in strings:
+            if not isinstance(s, string_types):
+                raise TypeError("SQL identifier parts must be strings")
+
+        super(Identifier, self).__init__(strings)
+
+    @property
+    def strings(self):
+        """A tuple with the strings wrapped by the `Identifier`."""
+        return self._wrapped
 
     @property
     def string(self):
-        """The string wrapped by the `Identifier`."""
-        return self._wrapped
+        """The string wrapped by the `Identifier`.
+        """
+        if len(self._wrapped) == 1:
+            return self._wrapped[0]
+        else:
+            raise AttributeError(
+                "the Identifier wraps more than one than one string")
+
+    def __repr__(self):
+        return "%s(%s)" % (
+            self.__class__.__name__,
+            ', '.join(map(repr, self._wrapped)))
 
     def as_string(self, context):
-        return ext.quote_ident(self._wrapped, context)
+        return '.'.join(ext.quote_ident(s, context) for s in self._wrapped)
 
 
 class Literal(Composable):

tests/test_sql.py

@@ -24,9 +24,8 @@
 
 import datetime as dt
 import unittest
-from .testutils import (ConnectingTestCase,
-    skip_before_postgres, skip_before_python, skip_copy_if_green,
-    StringIO)
+from .testutils import (
+    ConnectingTestCase, skip_before_postgres, skip_copy_if_green, StringIO)
 
 import psycopg2
 from psycopg2 import sql
@@ -181,26 +180,43 @@ class IdentifierTests(ConnectingTestCase):
     def test_init(self):
         self.assert_(isinstance(sql.Identifier('foo'), sql.Identifier))
         self.assert_(isinstance(sql.Identifier(u'foo'), sql.Identifier))
+        self.assert_(isinstance(sql.Identifier('foo', 'bar', 'baz'), sql.Identifier))
+        self.assertRaises(TypeError, sql.Identifier)
         self.assertRaises(TypeError, sql.Identifier, 10)
         self.assertRaises(TypeError, sql.Identifier, dt.date(2016, 12, 31))
 
-    def test_string(self):
+    def test_strings(self):
+        self.assertEqual(sql.Identifier('foo').strings, ('foo',))
+        self.assertEqual(sql.Identifier('foo', 'bar').strings, ('foo', 'bar'))
+
+        # Legacy method
         self.assertEqual(sql.Identifier('foo').string, 'foo')
+        self.assertRaises(AttributeError,
+            getattr, sql.Identifier('foo', 'bar'), 'string')
 
     def test_repr(self):
         obj = sql.Identifier("fo'o")
         self.assertEqual(repr(obj), 'Identifier("fo\'o")')
         self.assertEqual(repr(obj), str(obj))
 
+        obj = sql.Identifier("fo'o", 'ba"r')
+        self.assertEqual(repr(obj), 'Identifier("fo\'o", \'ba"r\')')
+        self.assertEqual(repr(obj), str(obj))
+
     def test_eq(self):
         self.assert_(sql.Identifier('foo') == sql.Identifier('foo'))
+        self.assert_(sql.Identifier('foo', 'bar') == sql.Identifier('foo', 'bar'))
         self.assert_(sql.Identifier('foo') != sql.Identifier('bar'))
         self.assert_(sql.Identifier('foo') != 'foo')
         self.assert_(sql.Identifier('foo') != sql.SQL('foo'))
 
     def test_as_str(self):
-        self.assertEqual(sql.Identifier('foo').as_string(self.conn), '"foo"')
-        self.assertEqual(sql.Identifier("fo'o").as_string(self.conn), '"fo\'o"')
+        self.assertEqual(
+            sql.Identifier('foo').as_string(self.conn), '"foo"')
+        self.assertEqual(
+            sql.Identifier('foo', 'bar').as_string(self.conn), '"foo"."bar"')
+        self.assertEqual(
+            sql.Identifier("fo'o", 'ba"r').as_string(self.conn), '"fo\'o"."ba""r"')
 
     def test_join(self):
         self.assert_(not hasattr(sql.Identifier('foo'), 'join'))