Iterators QuerySet Method (#688)

* feat: add iterator function with sample docstring

* feat: implement the iterator queryset method

* feat: completed the docstring of iterator method

* test: write test function to check iterator result

* refactor: use iterate method instead fetch_all

* fix: debuging syntax error in kwargs of iterator

* feat: write a base sample doc for iterator method

* refactor: add ouput comment iterator docs example

* refactor: check change pk yield ormar model

* test: write new test to coverage iterator queryset

* fix: debuging new user model class 3 number

* fix: iterate on user3 model class

* fix: debug id field in user3 model by main user

* fix: remove prefetch_related for iterator method

* fix: debug mypy test for type annotation

* fix: added type annotation for rows variable

* simplify row checks as processing is expensive, raise exception on prefetch_related with iterator

* fix coverage

* fix mypy, bump mypy in pre-commit to newest version

* refactor: update document and test uuid pk type

* feat: write docs of iterate in quesrysetproxy

* feat: write iterate method querysetproxy tests

* fix: debuging new test written uuid pk

* refactor: seperate iterate test modules

* refactor: change description and handle empty set

* feat: added iterate method in readme files

* fix: set pragma: no cover for raised test

Co-authored-by: collerek <collerek@gmail.com>

docs/index.md

@@ -604,6 +604,7 @@ metadata.drop_all(engine)
 *  `bulk_update(objects: List[Model], columns: List[str] = None) -> None`
 *  `delete(*args, each: bool = False, **kwargs) -> int`
 *  `all(*args, **kwargs) -> List[Optional[Model]]`
+*  `iterate(*args, **kwargs) -> AsyncGenerator[Model]`
 *  `filter(*args, **kwargs) -> QuerySet`
 *  `exclude(*args, **kwargs) -> QuerySet`
 *  `select_related(related: Union[List, str]) -> QuerySet`

docs/queries/read.md

@@ -173,6 +173,45 @@ tracks = await Track.objects.all()
 
 ```
 
+## iterate
+
+`iterate(*args, **kwargs) -> AsyncGenerator["Model"]`
+
+Return async iterable generator for all rows from a database for given model.
+
+Passing args and/or kwargs is a shortcut and equals to calling `filter(*args, **kwargs).iterate()`.
+
+If there are no rows meeting the criteria an empty async generator is returned.
+
+```python
+class Album(ormar.Model):
+    class Meta:
+        tablename = "album"
+        metadata = metadata
+        database = database
+
+    id: int = ormar.Integer(primary_key=True)
+    name: str = ormar.String(max_length=100)
+```
+
+```python
+await Album.objects.create(name='The Cat')
+await Album.objects.create(name='The Dog')
+# will asynchronously iterate all Album models yielding one main model at a time from the generator
+async for album in Album.objects.iterate():
+    print(album.name)
+
+# The Cat
+# The Dog
+
+```
+
+!!!warning
+    Use of `iterate()` causes previous `prefetch_related()` calls to be ignored;
+    since these two optimizations do not make sense together.
+
+    If `iterate()` & `prefetch_related()` are used together the `QueryDefinitionError` exception is raised.
+
 ## Model methods
 
 Each model instance have a set of methods to `save`, `update` or `load` itself.
@@ -235,4 +274,4 @@ objects from other side of the relation.
     To read more about `QuerysetProxy` visit [querysetproxy][querysetproxy] section
 
 
-[querysetproxy]: ../relations/queryset-proxy.md
+[querysetproxy]: ../relations/queryset-proxy.md

docs/relations/queryset-proxy.md

@@ -84,6 +84,23 @@ assert news_posts[0].author == guido
 !!!tip
     Read more in queries documentation [all][all]
 
+### iterate
+
+`iterate(**kwargs) -> AsyncGenerator["Model"]`
+
+To iterate on related models use `iterate()` method.
+
+Note that you can filter the queryset, select related, exclude fields etc. like in normal query.
+
+```python
+# iterate on categories of this post with an async generator
+async for category in post.categories.iterate():
+    print(category.name)
+```
+
+!!!tip
+    Read more in queries documentation [iterate][iterate]
+
 ## Insert/ update data into database
 
 ### create
@@ -294,6 +311,7 @@ Returns a bool value to confirm if there are rows matching the given criteria (a
 [queries]: ../queries/index.md
 [get]: ../queries/read.md#get
 [all]: ../queries/read.md#all
+[iterate]: ../queries/read.md#iterate
 [create]: ../queries/create.md#create
 [get_or_create]: ../queries/read.md#get_or_create
 [update_or_create]: ../queries/update.md#update_or_create