documentation

README.rst

@@ -32,9 +32,9 @@ Models are defined in a way reminiscent of Django's ORM:
 
         engine = engines.MergeTree('birthday', ('first_name', 'last_name', 'birthday'))
 
-It is possible to provide a default value for a field, instead of it's "natural" default (empty string for string fields, zero for numeric fields etc.).
+It is possible to provide a default value for a field, instead of its "natural" default (empty string for string fields, zero for numeric fields etc.).
 
-See below for the supported model field types.
+See below for the supported field types and table engines.
 
 Using Models
 ------------
@@ -48,8 +48,8 @@ Once you have a model, you can create model instances:
     >>> dan.first_name
     u'Dan'
 
-When values are assigned to a model fields, they are immediately converted to their Pythonic data type.
-In case the value is invalid, a ValueError is raised:
+When values are assigned to model fields, they are immediately converted to their Pythonic data type.
+In case the value is invalid, a ``ValueError`` is raised:
 
 .. code:: python
 
@@ -61,7 +61,10 @@ In case the value is invalid, a ValueError is raised:
     >>> suzy.birthday = '1922-05-31'
     ValueError: DateField out of range - 1922-05-31 is not between 1970-01-01 and 2038-01-19
 
-To write your instances to ClickHouse, you need a Database instance:
+Inserting to the Database
+-------------------------
+
+To write your instances to ClickHouse, you need a ``Database`` instance:
 
 .. code:: python
 
@@ -76,16 +79,53 @@ If necessary, you can specify a different database URL and optional credentials:
 
     db = Database('my_test_db', db_url='http://192.168.1.1:8050', username='scott', password='tiger')
 
-Using the Database instance you can create a table for your model, and insert instances to it:
+Using the ``Database`` instance you can create a table for your model, and insert instances to it:
 
 .. code:: python
 
     db.create_table(Person)
     db.insert([dan, suzy])
 
-The insert method can take any iterable of model instances, but they all must belong to the same model class.
+The ``insert`` method can take any iterable of model instances, but they all must belong to the same model class.
 
+Reading from the Database
+-------------------------
 
+Loading model instances from the database is simple:
+
+.. code:: python
+
+    for person in db.select("SELECT * FROM my_test_db.person", model_class=Person):
+        print person.first_name, person.last_name
+
+Do not include a ``FORMAT`` clause in the query, since the ORM automatically sets the format to ``TabSeparatedWithNamesAndTypes``.
+
+It is possible to select only a subset of the columns, and the rest will receive their default values:
+
+.. code:: python
+
+    for person in db.select("SELECT first_name FROM my_test_db.person WHERE last_name='Smith'", model_class=Person):
+        print person.first_name
+
+Specifying a model class is not required. In case you do not provide a model class, an ad-hoc class will
+be defined based on the column names and types returned by the query:
+
+.. code:: python
+
+    for row in db.select("SELECT max(height) as max_height FROM my_test_db.person"):
+        print row.max_height
+
+Counting
+--------
+
+The ``Database`` class also supports counting records easily:
+
+.. code:: python
+
+    >>> db.count(Person)
+    117
+    >>> db.count(Person, conditions="height > 1.90")
+    6
 
 Field Types
 -----------
@@ -106,6 +146,10 @@ Currently the following field types are supported:
 - DateField
 - DateTimeField
 
+Table Engines
+-------------
+
+TBD
 
 
 Development
@@ -119,4 +163,4 @@ After cloning the project, run the following commands::
 
 To run the tests, ensure that the ClickHouse server is running on http://localhost:8123/ (this is the default), and run::
 
-    bin/nosetests
+    bin/nosetests

src/infi/clickhouse_orm/database.py

@@ -17,6 +17,7 @@ class Database(object):
         self._send('CREATE DATABASE IF NOT EXISTS ' + db_name)
 
     def create_table(self, model_class):
+        # TODO check that model has an engine
         self._send(model_class.create_table_sql(self.db_name))
 
     def drop_table(self, model_class):

src/infi/clickhouse_orm/fields.py

@@ -15,23 +15,30 @@ class Field(object):
         self.default = default or self.class_default
 
     def to_python(self, value):
-        """
+        '''
         Converts the input value into the expected Python data type, raising ValueError if the
         data can't be converted. Returns the converted value. Subclasses should override this.
-        """
+        '''
         return value
 
     def validate(self, value):
+        '''
+        Called after to_python to validate that the value is suitable for the field's database type.
+        Subclasses should override this.
+        '''
         pass
 
     def _range_check(self, value, min_value, max_value):
+        '''
+        Utility method to check that the given value is between min_value and max_value.
+        '''
         if value < min_value or value > max_value:
             raise ValueError('%s out of range - %s is not between %s and %s' % (self.__class__.__name__, value, min_value, max_value))
 
     def get_db_prep_value(self, value):
-        """
+        '''
         Returns the field's value prepared for interacting with the database.
-        """
+        '''
         return value
 
 

src/infi/clickhouse_orm/models.py

@@ -58,6 +58,10 @@ class Model(object):
                 setattr(self, name, field.default)
 
     def __setattr__(self, name, value):
+        '''
+        When setting a field value, converts the value to its Pythonic type and validates it.
+        This may raise a ValueError.
+        '''
         field = self.get_field(name)
         if field:
             value = field.to_python(value)
@@ -65,15 +69,24 @@ class Model(object):
         super(Model, self).__setattr__(name, value)
 
     def get_field(self, name):
+        '''
+        Get a Field instance given its name, or None if not found.
+        '''
         field = getattr(self.__class__, name, None)
         return field if isinstance(field, Field) else None
 
     @classmethod
     def table_name(cls):
+        '''
+        Returns the model's database table name.
+        '''
         return cls.__name__.lower()
 
     @classmethod
     def create_table_sql(cls, db_name):
+        '''
+        Returns the SQL command for creating a table for this model.
+        '''
         parts = ['CREATE TABLE IF NOT EXISTS %s.%s (' % (db_name, cls.table_name())]
         cols = []
         for name, field in cls._fields:
@@ -86,6 +99,9 @@ class Model(object):
 
     @classmethod
     def drop_table_sql(cls, db_name):
+        '''
+        Returns the SQL command for deleting this model's table.
+        '''
         return 'DROP TABLE IF EXISTS %s.%s' % (db_name, cls.table_name())
 
     @classmethod