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38 lines
1.4 KiB
Plaintext
38 lines
1.4 KiB
Plaintext
=====================================
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PostgreSQL specific query expressions
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=====================================
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.. module:: django.contrib.postgres.expressions
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:synopsis: PostgreSQL specific query expressions
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These expressions are available from the
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``django.contrib.postgres.expressions`` module.
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``ArraySubquery()`` expressions
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===============================
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.. class:: ArraySubquery(queryset)
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``ArraySubquery`` is a :class:`~django.db.models.Subquery` that uses the
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PostgreSQL ``ARRAY`` constructor to build a list of values from the queryset,
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which must use :meth:`.QuerySet.values` to return only a single column.
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This class differs from :class:`~django.contrib.postgres.aggregates.ArrayAgg`
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in the way that it does not act as an aggregate function and does not require
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an SQL ``GROUP BY`` clause to build the list of values.
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For example, if you want to annotate all related books to an author as JSON
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objects:
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.. code-block:: pycon
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>>> from django.db.models import OuterRef
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>>> from django.db.models.functions import JSONObject
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>>> from django.contrib.postgres.expressions import ArraySubquery
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>>> books = Book.objects.filter(author=OuterRef('pk')).values(
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... json=JSONObject(title='title', pages='pages')
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... )
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>>> author = Author.objects.annotate(books=ArraySubquery(books)).first()
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>>> author.books
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[{'title': 'Solaris', 'pages': 204}, {'title': 'The Cyberiad', 'pages': 295}]
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