Add $table and $db placeholders

README.rst

@@ -91,6 +91,25 @@ It is possible to select only a subset of the columns, and the rest will receive
     for person in db.select("SELECT first_name FROM my_test_db.person WHERE last_name='Smith'", model_class=Person):
         print person.first_name
 
+SQL Placeholders
+****************
+
+There are a couple of special placeholders that you can use inside the SQL to make it easier to write:
+``$db`` and ``$table``. The first one is replaced by the database name, and the second is replaced by
+the database name plus table name (but is available only when the model is specified).
+
+So instead of this::
+
+    db.select("SELECT * FROM my_test_db.person", model_class=Person)
+
+you can use::
+
+    db.select("SELECT * FROM $db.person", model_class=Person)
+
+or even::
+
+    db.select("SELECT * FROM $table", model_class=Person)
+
 Ad-Hoc Models
 *************
 

src/infi/clickhouse_orm/database.py

@@ -5,6 +5,7 @@ from utils import escape, parse_tsv, import_submodules
 from math import ceil
 import datetime
 import logging
+from string import Template
 
 
 Page = namedtuple('Page', 'objects number_of_objects pages_total number page_size')
@@ -41,7 +42,7 @@ class Database(object):
             return # model_instances is empty
         model_class = first_instance.__class__
         def gen():
-            yield 'INSERT INTO `%s`.`%s` FORMAT TabSeparated\n' % (self.db_name, model_class.table_name())
+            yield self._substitute('INSERT INTO $table FORMAT TabSeparated\n', model_class)
             yield first_instance.to_tsv()
             yield '\n'
             for instance in i:
@@ -50,14 +51,16 @@ class Database(object):
         self._send(gen())
 
     def count(self, model_class, conditions=None):
-        query = 'SELECT count() FROM `%s`.`%s`' % (self.db_name, model_class.table_name())
+        query = 'SELECT count() FROM $table'
         if conditions:
             query += ' WHERE ' + conditions
+        query = self._substitute(query, model_class)
         r = self._send(query)
         return int(r.text) if r.text else 0
 
     def select(self, query, model_class=None, settings=None):
         query += ' FORMAT TabSeparatedWithNamesAndTypes'
+        query = self._substitute(query, model_class)
         r = self._send(query, settings, True)
         lines = r.iter_lines()
         field_names = parse_tsv(next(lines))
@@ -70,11 +73,12 @@ class Database(object):
         count = self.count(model_class, conditions)
         pages_total = int(ceil(count / float(page_size)))
         offset = (page_num - 1) * page_size
-        query = 'SELECT * FROM `%s`.`%s`' % (self.db_name, model_class.table_name())
+        query = 'SELECT * FROM $table'
         if conditions:
             query += ' WHERE ' + conditions
         query += ' ORDER BY %s' % order_by
         query += ' LIMIT %d, %d' % (offset, page_size)
+        query = self._substitute(query, model_class)
         return Page(
             objects=list(self.select(query, model_class, settings)),
             number_of_objects=count,
@@ -100,7 +104,8 @@ class Database(object):
     def _get_applied_migrations(self, migrations_package_name):
         from migrations import MigrationHistory
         self.create_table(MigrationHistory)
-        query = "SELECT module_name from `%s`.`%s` WHERE package_name = '%s'" % (self.db_name, MigrationHistory.table_name(), migrations_package_name)
+        query = "SELECT module_name from $table WHERE package_name = '%s'" % migrations_package_name
+        query = self._substitute(query, MigrationHistory)
         return set(obj.module_name for obj in self.select(query))
 
     def _send(self, data, settings=None, stream=False):
@@ -117,3 +122,14 @@ class Database(object):
         if self.password:
             params['password'] = password
         return params
+
+    def _substitute(self, query, model_class=None):
+        '''
+        Replaces $db and $table placeholders in the query.
+        '''
+        if '$' in query:
+            mapping = dict(db="`%s`" % self.db_name)
+            if model_class:
+                mapping['table'] = "`%s`.`%s`" % (self.db_name, model_class.table_name())
+            query = Template(query).substitute(mapping)
+        return query

tests/test_migrations.py

@@ -22,7 +22,7 @@ class MigrationsTestCase(unittest.TestCase):
         self.database.drop_table(MigrationHistory)
 
     def tableExists(self, model_class):
-        query = "EXISTS TABLE `%s`.`%s`" % (self.database.db_name, model_class.table_name())
+        query = "EXISTS TABLE $db.`%s`" % model_class.table_name()
         return next(self.database.select(query)).result == 1
 
     def getTableFields(self, model_class):