Django CTE Trees is an experimental implementation of Adjacency-List trees using
PostgreSQL Common Table Expressions (CTE). Its aim is to completely hide the
management of tree structure, as well as explore the issues related to including
CTE in the Django ORM.
Although handling tree structure in a transparent way is a desirable
characteristic for many applications, the currently known limitations of
including CTE (see below) will be a show-stopper for many other applications.
Unless you know beforehand that these limitations will not affect your
application, this module is not suitable for you, and you should use an
actively managed tree structure (such as
django-mptt <https://github.com/django-mptt/django-mptt/> or
- Simple: inheriting from an abstract node model is sufficient to obtain tree
functionality for any Model.
- Seamless: does not use RawQuerySet, so queries using CTE can be combined with
normal Django queries, and won’t confuse the SQLCompiler or other QuerySets,
including using multiple databases.
- Self-contained: tree nodes can be manipulated without worrying about
maintaining tree structure in the database.
- Single query: all tree traversal operations can be performed through a single
query, including children, siblings, ancestors, roots, and descendants.
- Flexible ordering: supports (a subset of) normal Django ordering as well as
ordering on tree structure information, including depth and path, in DFS and
- Multiple delete semantics: supports Pharaoh, Grandmother, and Monarchy
- Code: unit tests, documentation, comments.
- Virtual fields not usable in external queries: it is not yet possible to use
the virtual fields which describe the tree structure (depth, path, and
ordering information) in queries other than directly on the CTE Nodes.
Consequently, you cannot order on these fields any Model other than the CTE
Nodes themselves. See the technical notes for details.
- Cannot merge queries with OR: because CTE relies on custom WHERE clauses added
through extra, the bitwise OR operator cannot be used with query composition.
- Cannot use new Nodes without loading: immediately after creating a CTE Node,
it must be read from the database if you need to use its tree structure
(depth, path, and ordering information).
- Cannot order descending: you cannot order on structure fields (depth, path) or
additional normal fields combined with structure fields in descending order.
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