203 lines
5.4 KiB
Markdown
203 lines
5.4 KiB
Markdown
# QuerySetProxy
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When access directly the related `ManyToMany` field as well as `ReverseForeignKey` 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, select related etc related models directly from parent model.
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!!!note
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By default exposed QuerySet is already filtered to return only `Models` related to parent `Model`.
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So if you issue `post.categories.all()` you will get all categories related to that post, not all in table.
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!!!note
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Note that when accessing QuerySet API methods through QuerysetProxy you don't
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need to use `objects` attribute like in normal queries.
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So note that it's `post.categories.all()` and **not** `post.categories.objects.all()`.
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To learn more about available QuerySet methods visit [queries][queries]
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!!!warning
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Querying related models from ManyToMany cleans list of related models loaded on parent model:
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Example: `post.categories.first()` will set post.categories to list of 1 related model -> the one returned by first()
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Example 2: if post has 4 categories so `len(post.categories) == 4` calling `post.categories.limit(2).all()`
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-> will load only 2 children and now `assert len(post.categories) == 2`
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This happens for all QuerysetProxy methods returning data: `get`, `all` and `first` and in `get_or_create` if model already exists.
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Note that value returned by `create` or created in `get_or_create` and `update_or_create`
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if model does not exist will be added to relation list (not clearing it).
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## get
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`get(**kwargs): -> Model`
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To grab just one of related models filtered by name you can use `get(**kwargs)` method.
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```python
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# grab one category
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assert news == await post.categories.get(name="News")
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# note that method returns the category so you can grab this value
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# but it also modifies list of related models in place
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# so regardless of what was previously loaded on parent model
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# now it has only one value -> just loaded with get() call
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assert len(post.categories) == 1
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assert post.categories[0] == news
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```
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!!!tip
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Read more in queries documentation [get][get]
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## all
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`all(**kwargs) -> List[Optional["Model"]]`
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To get a list of related models use `all()` method.
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Note that you can filter the queryset, select related, exclude fields etc. like in normal query.
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```python
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# with all Queryset methods - filtering, selecting columns, counting etc.
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await news.posts.filter(title__contains="M2M").all()
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await Category.objects.filter(posts__author=guido).get()
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# columns models of many to many relation can be prefetched
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news_posts = await news.posts.select_related("author").all()
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assert news_posts[0].author == guido
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```
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!!!tip
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Read more in queries documentation [all][all]
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## create
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`create(**kwargs): -> Model`
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Create related `Model` directly from parent `Model`.
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The link table is automatically populated, as well as relation ids in the database.
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```python
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# Creating columns object from instance:
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await post.categories.create(name="Tips")
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assert len(await post.categories.all()) == 2
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# newly created instance already have relation persisted in the database
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```
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!!!tip
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Read more in queries documentation [create][create]
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## get_or_create
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`get_or_create(**kwargs) -> Model`
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!!!tip
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Read more in queries documentation [get_or_create][get_or_create]
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## update_or_create
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`update_or_create(**kwargs) -> Model`
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!!!tip
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Read more in queries documentation [update_or_create][update_or_create]
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## filter
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`filter(**kwargs) -> QuerySet`
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!!!tip
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Read more in queries documentation [filter][filter]
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## exclude
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`exclude(**kwargs) -> QuerySet`
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!!!tip
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Read more in queries documentation [exclude][exclude]
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## select_related
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`select_related(related: Union[List, str]) -> QuerySet`
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!!!tip
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Read more in queries documentation [select_related][select_related]
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## prefetch_related
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`prefetch_related(related: Union[List, str]) -> QuerySet`
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!!!tip
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Read more in queries documentation [prefetch_related][prefetch_related]
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## limit
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`limit(limit_count: int) -> QuerySet`
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!!!tip
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Read more in queries documentation [limit][limit]
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## offset
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`offset(offset: int) -> QuerySet`
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!!!tip
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Read more in queries documentation [offset][offset]
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## count
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`count() -> int`
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!!!tip
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Read more in queries documentation [count][count]
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## exists
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`exists() -> bool`
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!!!tip
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Read more in queries documentation [exists][exists]
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## fields
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`fields(columns: Union[List, str, set, dict]) -> QuerySet`
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!!!tip
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Read more in queries documentation [fields][fields]
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## exclude_fields
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`exclude_fields(columns: Union[List, str, set, dict]) -> QuerySet`
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!!!tip
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Read more in queries documentation [exclude_fields][exclude_fields]
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## order_by
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`order_by(columns:Union[List, str]) -> QuerySet`
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!!!tip
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Read more in queries documentation [order_by][order_by]
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[queries]: ../queries.md
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[get]: ../queries.md#get
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[all]: ../queries.md#all
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[create]: ../queries.md#create
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[get_or_create]: ../queries.md#get_or_create
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[update_or_create]: ../queries.md#update_or_create
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[filter]: ../queries.md#filter
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[exclude]: ../queries.md#exclude
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[select_related]: ../queries.md#select_related
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[prefetch_related]: ../queries.md#prefetch_related
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[limit]: ../queries.md#limit
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[offset]: ../queries.md#offset
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[count]: ../queries.md#count
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[exists]: ../queries.md#exists
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[fields]: ../queries.md#fields
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[exclude_fields]: ../queries.md#exclude_fields
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[order_by]: ../queries.md#order_by |