Add AlterTableWithBuffer migration operation

CHANGELOG.md

@@ -1,6 +1,10 @@
 Change Log
 ==========
 
+Unreleased
+----------
+- Add `AlterTableWithBuffer` migration operation
+
 v0.9.6
 ------
 - Fix python3 compatibility (TvoroG)

docs/schema_migrations.md

@@ -34,11 +34,13 @@ The following operations are supported:
 
 **CreateTable**
 
-A migration operation that creates a table for a given model class.
+A migration operation that creates a table for a given model class. If the table already exists, the operation does nothing.
+
+In case the model class is a `BufferModel`, the operation first creates the underlying on-disk table, and then creates the buffer table.
 
 **DropTable**
 
-A migration operation that drops the table of a given model class.
+A migration operation that drops the table of a given model class. If the table does not exist, the operation does nothing.
 
 **AlterTable**
 
@@ -50,6 +52,13 @@ A migration operation that compares the table of a given model class to the mode
 
 Default values are not altered by this operation.
 
+**AlterTableWithBuffer**
+
+A compound migration operation for altering a buffer table and its underlying on-disk table. The buffer table is dropped, the on-disk table is altered, and then the buffer table is re-created. This is the procedure recommended in the ClickHouse documentation for handling scenarios in which the underlying table needs to be modified.
+
+Applying this migration operation to a regular table has the same effect as an `AlterTable` operation.
+
+
 Running Migrations
 ------------------
 

src/infi/clickhouse_orm/migrations.py

@@ -82,6 +82,25 @@ class AlterTable(Operation):
                 self._alter_table(database, 'MODIFY COLUMN %s %s' % model_field)
 
 
+class AlterTableWithBuffer(Operation):
+    '''
+    A migration operation for altering a buffer table and its underlying on-disk table.
+    The buffer table is dropped, the on-disk table is altered, and then the buffer table
+    is re-created.
+    '''
+
+    def __init__(self, model_class):
+        self.model_class = model_class
+
+    def apply(self, database):
+        if issubclass(self.model_class, BufferModel):
+            DropTable(self.model_class).apply(database)
+            AlterTable(self.model_class.engine.main_model).apply(database)
+            CreateTable(self.model_class).apply(database)
+        else:
+            AlterTable(self.model_class).apply(database)
+
+
 class DropTable(Operation):
     '''
     A migration operation that drops the table of a given model class.
@@ -91,7 +110,7 @@ class DropTable(Operation):
         self.model_class = model_class
 
     def apply(self, database):
-        logger.info('    Drop table %s', self.model_class.__name__)
+        logger.info('    Drop table %s', self.model_class.table_name())
         database.drop_table(self.model_class)
 
 

tests/sample_migrations/0010.py

@@ -0,0 +1,6 @@
+from infi.clickhouse_orm import migrations
+from ..test_migrations import *
+
+operations = [
+    migrations.CreateTable(Model4Buffer)
+]

tests/sample_migrations/0011.py

@@ -0,0 +1,6 @@
+from infi.clickhouse_orm import migrations
+from ..test_migrations import *
+
+operations = [
+    migrations.AlterTableWithBuffer(Model4Buffer_changed)
+]

tests/test_migrations.py

@@ -2,7 +2,7 @@ from __future__ import unicode_literals
 import unittest
 
 from infi.clickhouse_orm.database import Database
-from infi.clickhouse_orm.models import Model
+from infi.clickhouse_orm.models import Model, BufferModel
 from infi.clickhouse_orm.fields import *
 from infi.clickhouse_orm.engines import *
 from infi.clickhouse_orm.migrations import MigrationHistory
@@ -61,6 +61,7 @@ class MigrationsTestCase(unittest.TestCase):
         self.assertTrue(self.tableExists(EnumModel1))
         self.assertEquals(self.getTableFields(EnumModel2),
                           [('date', 'Date'), ('f1', "Enum16('dog' = 1, 'cat' = 2, 'horse' = 3, 'pig' = 4)")])
+        # Materialized fields and alias fields
         self.database.migrate('tests.sample_migrations', 8)
         self.assertTrue(self.tableExists(MaterializedModel))
         self.assertEquals(self.getTableFields(MaterializedModel),
@@ -69,6 +70,15 @@ class MigrationsTestCase(unittest.TestCase):
         self.assertTrue(self.tableExists(AliasModel))
         self.assertEquals(self.getTableFields(AliasModel),
                           [('date', 'Date'), ('date_alias', "Date")])
+        # Buffer models creation and alteration
+        self.database.migrate('tests.sample_migrations', 10)
+        self.assertTrue(self.tableExists(Model4))
+        self.assertTrue(self.tableExists(Model4Buffer))
+        self.assertEquals(self.getTableFields(Model4), [('date', 'Date'), ('f1', 'Int32'), ('f2', 'String')])
+        self.assertEquals(self.getTableFields(Model4Buffer), [('date', 'Date'), ('f1', 'Int32'), ('f2', 'String')])
+        self.database.migrate('tests.sample_migrations', 11)
+        self.assertEquals(self.getTableFields(Model4), [('date', 'Date'), ('f3', 'DateTime'), ('f2', 'String')])
+        self.assertEquals(self.getTableFields(Model4Buffer), [('date', 'Date'), ('f3', 'DateTime'), ('f2', 'String')])
 
 
 # Several different models with the same table name, to simulate a table that changes over time
@@ -159,3 +169,47 @@ class AliasModel(Model):
     @classmethod
     def table_name(cls):
         return 'alias_date'
+
+
+class Model4(Model):
+
+    date = DateField()
+    f1 = Int32Field()
+    f2 = StringField()
+
+    engine = MergeTree('date', ('date',))
+
+    @classmethod
+    def table_name(cls):
+        return 'model4'
+
+
+class Model4Buffer(BufferModel, Model4):
+
+    engine = Buffer(Model4)
+
+    @classmethod
+    def table_name(cls):
+        return 'model4buffer'
+
+
+class Model4_changed(Model):
+
+    date = DateField()
+    f3 = DateTimeField()
+    f2 = StringField()
+
+    engine = MergeTree('date', ('date',))
+
+    @classmethod
+    def table_name(cls):
+        return 'model4'
+
+
+class Model4Buffer_changed(BufferModel, Model4_changed):
+
+    engine = Buffer(Model4_changed)
+
+    @classmethod
+    def table_name(cls):
+        return 'model4buffer'