Added docs about databases and queries

docs/configuration.md

@@ -10,8 +10,7 @@ You can change `CLICKHOUSE_` prefix in settings using this parameter to anything
 ### CLICKHOUSE_DATABASES
 Defaults to: `{}`  
 A dictionary, defining databases in django-like style.  
-<!--- TODO Add link  --->
-Key is an alias to communicate with this database in [connections]() and [using]().  
+Key is an alias to communicate with this database in [connections](databases.md#getting-database-objects) and [using](routing.md#settings-database-in-queryset).  
 Value is a configuration dict with parameters:
 * [infi.clickhouse_orm database parameters](https://github.com/Infinidat/infi.clickhouse_orm/blob/develop/docs/class_reference.md#database)
 * `migrate: bool` - indicates if this database should be migrated. See [migrations](migrations.md).  
@@ -35,8 +34,7 @@ CLICKHOUSE_DATABASES = {
 
 ### CLICKHOUSE_DEFAULT_DB_ALIAS
 Defaults to: `'default'`  
-<!--- TODO Add link  --->
-A database alias to use in [QuerySets]() if direct [using]() is not specified.
+A database alias to use in [QuerySets](queries.md) if direct [using](routing.md#settings-database-in-queryset) is not specified.
 
 ### CLICKHOUSE_SYNC_STORAGE
 Defaults to: `'django_clickhouse.storages.RedisStorage'`  

docs/databases.md

@@ -0,0 +1,40 @@
+# Databases
+Direct usage of `Database` objects is not expected in this library. But in some cases, you may still need them.
+This section describes `Database` objects and there usage.
+
+`django_clickhouse.database.Database` is a class, describing a ClickHouse database connection.
+
+## Getting database objects
+To get a `Database` object by its alias name in [CLICKHOUSE_DATABASES](configuration.md#clickhouse_databases) 
+ use `django_clickhouse.database.connections` object. 
+This object is a `django_clickhouse.database.ConnectionProxy` instance:
+ it creates `Database` objects when they are used for the first time and stores them in memory.
+ 
+Example:
+```python
+from django_clickhouse.database import connections
+
+# Database objects are inited on first call
+db = connections['default']
+secondary = connections['secondary']
+
+# Already inited - object is returned from memory 
+db_link = connections['default']
+```
+
+## Database object
+Database class is based on [infi.clickhouse_orm Database object](https://github.com/Infinidat/infi.clickhouse_orm/blob/develop/docs/models_and_databases.md#models-and-databases),
+but extends it with some extra attributes and methods:
+
+### Database migrations are restricted
+I expect this library [migration system](migrations.md) to be used.
+Direct database migration will lead to migration information errors.
+
+### `insert_tuples` and `select_tuples` methods
+[infi.clickhouse_orm](https://github.com/Infinidat/infi.clickhouse_orm) store data rows in Model objects.
+It works well on hundreds of records. 
+But when you sync 100k records in a batch, initializing 100k model instances will be slow.  
+Too optimize this process `ClickHouseModel` class have `get_tuple_class()` method.
+It generates a [namedtuple](https://docs.python.org/3/library/collections.html#collections.namedtuple) class,
+with same data fields a model has. 
+Initializing such tuples takes much less time, then initializing Model objects.

docs/index.md

@@ -12,7 +12,8 @@
      * [DjangoModel](models.md#DjangoModel)
      * [ClickHouseModel](models.md#ClickHouseModel)
   * [Making queries](queries.md)
-  * [Database routing](routing.md)
+  * [Databases](models.md)
+     * [Routing](routing.md)
   * [Migrations](migrations.md)
   * [Synchronization](synchronization.md)
     * [Storages](storages.md)

docs/queries.md

@@ -1,13 +1,66 @@
 # Making queries
 
-## Motivation
-ClickHouse SQL language is near to standard, but does not follow it exactly ([docs](https://clickhouse.tech/docs/en/introduction/distinctive_features/#sql-support)).  
-It can not be easily integrated into django query subsystem as it expects databases to support standard SQL language features like transactions and INNER/OUTER JOINS by condition.  
+QuerySet system used by this library looks very similar to django, but it is implemented separately.
+You can read reasons for this design [here](motivation.md#separate-from-django-database-setting-queryset-and-migration-system).
 
-In order to fit it 
+## Usage
+Library query system extends [infi.clickhouse-orm QuerySet system](https://github.com/Infinidat/infi.clickhouse_orm/blob/develop/docs/querysets.md) and supports all it features.  
+In most cases you have no need to create querysets explicitly - just use `objects` attribute or `objects_in(db)` method of `ClickHouseModel`.  
+At the same time `django-clickhouse` adds some extra features to `QuerySet` and `AggregateQuerySet`. 
+They are available if your model inherits `django_clickhouse.clickhouse_models.ClickHouseModel`.
 
+## Extra features
+### Django-like routing system
+There's no need to set database object explicitly with `objects_in(...)` method, as original QuerySet expects.
+Database is determined based on library configuration and [router](routing.md#router) used.
 
+If you want to set database explicitly you can use any of approaches:
+* [infi approach](https://github.com/Infinidat/infi.clickhouse_orm/blob/develop/docs/querysets.md#querysets)
+* Django like `QuerySet.using(db_alias)` method
 
-Libraries query system extends [infi.clickhouse-orm](https://github.com/Infinidat/infi.clickhouse_orm/blob/develop/docs/querysets.md).
+Example:  
+```python
+from django_clickhouse.database import connections
+from my_app.clickhouse_models import ClickHouseUser
 
-TODO
+# This query will choose database using current router.
+# By default django_clickhouse.routers.DefaultRouter is used.
+# It gets one random database, from ClickHouseUser.read_db_aliases for read queries
+ClickHouseUser.objects.filter(id__in=[1,2,3]).count()
+
+# These queries do the same thing, using 'secondary' connection from CLICKHOUSE_DATABASES setting
+ClickHouseUser.objects_in(connections['secondary']).filter(id__in=[1,2,3]).count()
+ClickHouseUser.objects.filter(id__in=[1,2,3]).using('secondary').count()
+
+# You can get database to use with get_database(for_write: bool = False) method
+# Note that it if you have multiple database in model settings,
+#  DefaultRouter can return any of them each time function is called, function is stateless
+ClickHouseUser.objects.get_database(for_write=False)
+```
+
+### QuerySet create methods
+This library adds methods to add objects like django does without direct Database object usage.
+
+Example:  
+```python
+from datetime import date
+from my_app.clickhouse_models import ClickHouseUser
+
+# This queries will choose database using current router.
+# By default django_clickhouse.routers.DefaultRouter is used.
+# It gets one random database, from ClickHouseUser.write_db_aliases for write queries
+# You can set database explicitly with using(...) or objects_in(...) methods
+instance = ClickHouseUser.objects.create(id=1, first_name='Alice', visits=1, birthday=date(2003, 6, 1))
+objs = ClickHouseUser.objects.bulk_create([
+    ClickHouseUser(id=2, first_name='Bob', visits=2, birthday=date(2001, 5, 1)),
+    ClickHouseUser(id=3, first_name='Jhon', visits=3, birthday=date(2002, 7, 11))
+], batch_size=10)
+```
+
+### Getting all objects
+`QuerySet.all()` method returns copy of current QuerySet:
+```python
+from my_app.clickhouse_models import ClickHouseUser
+
+qs = ClickHouseUser.objects.all()
+```

docs/routing.md

@@ -54,8 +54,7 @@ class MyModel(ClickHouseModel):
  ```
 
 ## Settings database in QuerySet
-<!--- TODO Add link --->
-Database can be set in each [QuerySet]() explicitly by using one of methods:
+Database can be set in each [QuerySet](queries.md) explicitly by using one of methods:
 * With [infi approach](https://github.com/Infinidat/infi.clickhouse_orm/blob/develop/docs/querysets.md#querysets): `MyModel.objects_in(db_object).filter(id__in=[1,2,3]).count()`
 * With `using()` method: `MyModel.objects.filter(id__in=[1,2,3]).using(db_alias).count()`