work on docs in queries
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collerek
@ -1,6 +1,18 @@
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# Joins and subqueries
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To join one table to another, so load also related models you can use following methods.
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* `select_related(related: Union[List, str]) -> QuerySet`
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* `prefetch_related(related: Union[List, str]) -> QuerySet`
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* `Model`
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* `Model.load()` method
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* `QuerysetProxy`
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* `QuerysetProxy.select_related(related: Union[List, str])` method
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* `QuerysetProxy.prefetch_related(related: Union[List, str])` method
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## select_related
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@ -30,6 +42,30 @@ To chain related `Models` relation use double underscores between names.
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!!!tip
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To control order of models (both main or nested) use `order_by()` method.
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```python
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class Album(ormar.Model):
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class Meta:
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tablename = "albums"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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is_best_seller: bool = ormar.Boolean(default=False)
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class Track(ormar.Model):
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class Meta:
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tablename = "tracks"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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album: Optional[Album] = ormar.ForeignKey(Album)
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title: str = ormar.String(max_length=100)
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position: int = ormar.Integer()
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play_count: int = ormar.Integer(nullable=True)
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```
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```python
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album = await Album.objects.select_related("tracks").all()
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# will return album will all columns tracks
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@ -37,6 +73,52 @@ album = await Album.objects.select_related("tracks").all()
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You can provide a string or a list of strings
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```python
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class SchoolClass(ormar.Model):
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class Meta:
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tablename = "schoolclasses"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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department: Optional[Department] = ormar.ForeignKey(Department, nullable=False)
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class Category(ormar.Model):
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class Meta:
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tablename = "categories"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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class Student(ormar.Model):
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class Meta:
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tablename = "students"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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schoolclass: Optional[SchoolClass] = ormar.ForeignKey(SchoolClass)
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category: Optional[Category] = ormar.ForeignKey(Category, nullable=True)
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class Teacher(ormar.Model):
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class Meta:
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tablename = "teachers"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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schoolclass: Optional[SchoolClass] = ormar.ForeignKey(SchoolClass)
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category: Optional[Category] = ormar.ForeignKey(Category, nullable=True)
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```
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```python
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classes = await SchoolClass.objects.select_related(
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["teachers__category", "students"]).all()
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@ -81,12 +163,82 @@ To chain related `Models` relation use double underscores between names.
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!!!tip
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To control order of models (both main or nested) use `order_by()` method.
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```python
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class Album(ormar.Model):
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class Meta:
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tablename = "albums"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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is_best_seller: bool = ormar.Boolean(default=False)
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class Track(ormar.Model):
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class Meta:
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tablename = "tracks"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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album: Optional[Album] = ormar.ForeignKey(Album)
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title: str = ormar.String(max_length=100)
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position: int = ormar.Integer()
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play_count: int = ormar.Integer(nullable=True)
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```
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```python
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album = await Album.objects.prefetch_related("tracks").all()
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# will return album will all columns tracks
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```
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You can provide a string or a list of strings
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You can provide a string, or a list of strings
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```python
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class SchoolClass(ormar.Model):
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class Meta:
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tablename = "schoolclasses"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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department: Optional[Department] = ormar.ForeignKey(Department, nullable=False)
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class Category(ormar.Model):
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class Meta:
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tablename = "categories"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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class Student(ormar.Model):
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class Meta:
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tablename = "students"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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schoolclass: Optional[SchoolClass] = ormar.ForeignKey(SchoolClass)
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category: Optional[Category] = ormar.ForeignKey(Category, nullable=True)
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class Teacher(ormar.Model):
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class Meta:
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tablename = "teachers"
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metadata = metadata
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database = database
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id: int = ormar.Integer(primary_key=True)
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name: str = ormar.String(max_length=100)
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schoolclass: Optional[SchoolClass] = ormar.ForeignKey(SchoolClass)
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category: Optional[Category] = ormar.ForeignKey(Category, nullable=True)
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```
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```python
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classes = await SchoolClass.objects.prefetch_related(
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@ -221,3 +373,44 @@ That means that in `prefetch_related` example above if there are 3 distinct mode
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table B and 2 in table C, there will be only 5 children nested models shared between all
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model A instances. That also means that if you update any attribute it will be updated
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on all parents as they share the same child object.
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## Model methods
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Each model instance have a set of methods to `save`, `update` or `load` itself.
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### load
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You can load the `ForeignKey` related model by calling `load()` method.
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`load()` can be used to refresh the model from the database (if it was changed by some other process).
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!!!tip
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Read more about `load()` method in [models methods](../models/methods.md#load)
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## QuerysetProxy methods
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When access directly the related `ManyToMany` field as well as `ReverseForeignKey`
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returns the list of related models.
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But at the same time it exposes subset of QuerySet API, so you can filter, create,
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select related etc related models directly from parent model.
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### select_related
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Works exactly the same as [select_related](./#select_related) function above but allows you to fetch related
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objects from other side of the relation.
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!!!tip
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To read more about `QuerysetProxy` visit [querysetproxy][querysetproxy] section
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### prefetch_related
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Works exactly the same as [prefetch_related](./#prefetch_related) function above but allows you to fetch related
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objects from other side of the relation.
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!!!tip
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To read more about `QuerysetProxy` visit [querysetproxy][querysetproxy] section
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[querysetproxy]: ../relations/queryset-proxy.md
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