Readd db/db_save as deprecated methods

Author: tobiasdiez

src/sage/misc/all__sagemath_objects.py

@@ -20,7 +20,7 @@
 
 from sage.misc.flatten import flatten
 
-from sage.misc.persist import save, load, dumps, loads
+from sage.misc.persist import save, load, dumps, loads, db, db_save
 
 from sage.misc.constant_function import ConstantFunction
 

src/sage/misc/persist.pyx

@@ -44,7 +44,7 @@ comp = zlib
 comp_other = bz2
 
 from sage.misc.sage_unittest import TestSuite
-
+from sage.misc.superseded import deprecation
 
 # We define two global dictionaries `already_pickled` and
 # `already_unpickled`, which are intended to help you to implement
@@ -1222,3 +1222,31 @@ def load_sage_element(cls, parent, dic_pic):
     X._set_parent(parent)
     X.__dict__ = SageUnpickler.loads(dic_pic)
     return X
+
+
+def db(name):
+    r"""
+    Load object with given name from the Sage database. Use x.db(name)
+    or db_save(x, name) to save objects to the database.
+
+    The database directory is ``$HOME/.sage/db``.
+    """
+    deprecation(39012, "Directly use pickle/unpickle instead of db/db_save.")
+
+    from sage.misc.misc import SAGE_DB
+    return load('%s/%s' % (SAGE_DB, name))
+
+
+def db_save(x, name=None):
+    r"""
+    Save x to the Sage database.
+
+    The database directory is ``$HOME/.sage/db``.
+    """
+    deprecation(39012, "Directly use pickle/unpickle instead of db/db_save.")
+
+    try:
+        x.db(name)
+    except AttributeError:
+        from sage.misc.misc import SAGE_DB
+        save(x, '%s/%s' % (SAGE_DB, name))