- Added get_pk_constraint() to reflection.Inspector, similar

to get_primary_keys() except returns a dict that includes the
name of the constraint, for supported backends (PG so far).
[ticket:1769]
- Postgresql reflects the name of primary key constraints,
if one exists.  [ticket:1769]

5 files changed, 87 insertions, 7 deletions

diff --git a/lib/sqlalchemy/dialects/postgresql/base.py b/lib/sqlalchemy/dialects/postgresql/base.py
index 312ae9aa8..72251c8d5 100644
--- a/lib/sqlalchemy/dialects/postgresql/base.py
+++ b/lib/sqlalchemy/dialects/postgresql/base.py
@@ -1006,6 +1006,27 @@ class PGDialect(default.DefaultDialect):
         return primary_keys
 
     @reflection.cache
+    def get_pk_constraint(self, connection, table_name, schema=None, **kw):
+        cols = self.get_primary_keys(connection, table_name, schema=schema, **kw)
+        
+        table_oid = self.get_table_oid(connection, table_name, schema,
+                                       info_cache=kw.get('info_cache'))
+
+        PK_CONS_SQL = """
+        SELECT conname
+           FROM  pg_catalog.pg_constraint r
+           WHERE r.conrelid = :table_oid AND r.contype = 'p'
+           ORDER BY 1
+        """
+        t = sql.text(PK_CONS_SQL, typemap={'conname':sqltypes.Unicode})
+        c = connection.execute(t, table_oid=table_oid)
+        name = c.scalar()
+        return {
+            'constrained_columns':cols,
+            'name':name
+        }
+
+    @reflection.cache
     def get_foreign_keys(self, connection, table_name, schema=None, **kw):
         preparer = self.identifier_preparer
         table_oid = self.get_table_oid(connection, table_name, schema,
diff --git a/lib/sqlalchemy/engine/base.py b/lib/sqlalchemy/engine/base.py
index 4c5a6a82b..d35796063 100644
--- a/lib/sqlalchemy/engine/base.py
+++ b/lib/sqlalchemy/engine/base.py
@@ -260,8 +260,23 @@ class Dialect(object):
         Given a :class:`~sqlalchemy.engine.Connection`, a string
         `table_name`, and an optional string `schema`, return primary
         key information as a list of column names.
+
         """
+        raise NotImplementedError()
+
+    def get_pk_constraint(self, table_name, schema=None, **kw):
+        """Return information about the primary key constraint on `table_name`.
 
+        Given a string `table_name`, and an optional string `schema`, return
+        primary key information as a dictionary with these keys:
+
+        constrained_columns
+          a list of column names that make up the primary key
+
+        name
+          optional name of the primary key constraint.
+
+        """
         raise NotImplementedError()
 
     def get_foreign_keys(self, connection, table_name, schema=None, **kw):
diff --git a/lib/sqlalchemy/engine/default.py b/lib/sqlalchemy/engine/default.py
index 6fb0a14a5..fc49c62fa 100644
--- a/lib/sqlalchemy/engine/default.py
+++ b/lib/sqlalchemy/engine/default.py
@@ -205,6 +205,17 @@ class DefaultDialect(base.Dialect):
         insp = reflection.Inspector.from_engine(connection)
         return insp.reflecttable(table, include_columns)
 
+    def get_pk_constraint(self, conn, table_name, schema=None, **kw):
+        """Compatiblity method, adapts the result of get_primary_keys()
+        for those dialects which don't implement get_pk_constraint().
+        
+        """
+        return {
+            'constrained_columns':
+                        self.get_primary_keys(conn, table_name, 
+                                                schema=schema, **kw)
+        }
+        
     def validate_identifier(self, ident):
         if len(ident) > self.max_identifier_length:
             raise exc.IdentifierError(
diff --git a/lib/sqlalchemy/engine/reflection.py b/lib/sqlalchemy/engine/reflection.py
index 57f2205c1..56b9eafd8 100644
--- a/lib/sqlalchemy/engine/reflection.py
+++ b/lib/sqlalchemy/engine/reflection.py
@@ -189,6 +189,26 @@ class Inspector(object):
 
         return pkeys
 
+    def get_pk_constraint(self, table_name, schema=None, **kw):
+        """Return information about primary key constraint on `table_name`.
+
+        Given a string `table_name`, and an optional string `schema`, return
+        primary key information as a dictionary with these keys:
+        
+        constrained_columns
+          a list of column names that make up the primary key
+        
+        name
+          optional name of the primary key constraint.
+
+        """
+        pkeys = self.dialect.get_pk_constraint(self.conn, table_name, schema,
+                                              info_cache=self.info_cache,
+                                              **kw)
+
+        return pkeys
+        
+
     def get_foreign_keys(self, table_name, schema=None, **kw):
         """Return information about foreign_keys in `table_name`.
 
@@ -208,6 +228,9 @@ class Inspector(object):
           a list of column names in the referred table that correspond to
           constrained_columns
 
+        name
+          optional name of the foreign key constraint.
+          
         \**kw
           other options passed to the dialect's get_foreign_keys() method.
 
@@ -318,12 +341,14 @@ class Inspector(object):
             raise exc.NoSuchTableError(table.name)
 
         # Primary keys
-        primary_key_constraint = sa_schema.PrimaryKeyConstraint(*[
-            table.c[pk] for pk in self.get_primary_keys(table_name, schema, **tblkw)
-            if pk in table.c
-        ])
-
-        table.append_constraint(primary_key_constraint)
+        pk_cons = self.get_pk_constraint(table_name, schema, **tblkw)
+        if pk_cons:
+            primary_key_constraint = sa_schema.PrimaryKeyConstraint(*[
+                table.c[pk] for pk in pk_cons['constrained_columns']
+                if pk in table.c
+            ], name=pk_cons.get('name'))
+
+            table.append_constraint(primary_key_constraint)
 
         # Foreign keys
         fkeys = self.get_foreign_keys(table_name, schema, **tblkw)
diff --git a/lib/sqlalchemy/test/requires.py b/lib/sqlalchemy/test/requires.py
index bf911c2c2..1b9052fd8 100644
--- a/lib/sqlalchemy/test/requires.py
+++ b/lib/sqlalchemy/test/requires.py
@@ -11,7 +11,8 @@ from testing import \
      exclude, \
      emits_warning_on,\
      skip_if,\
-     fails_on
+     fails_on,\
+     fails_on_everything_except
 
 import testing
 import sys
@@ -245,6 +246,13 @@ def sane_rowcount(fn):
         fn,
         skip_if(lambda: not testing.db.dialect.supports_sane_rowcount)
     )
+
+def reflects_pk_names(fn):
+    """Target driver reflects the name of primary key constraints."""
+    return _chain_decorators_on(
+        fn,
+        fails_on_everything_except('postgresql')
+    )
     
 def python2(fn):
     return _chain_decorators_on(