django-tree-queries 0.5.0

Tree queries with explicit opt-in, without configurability

Query Django model trees using adjacency lists and recursive common table expressions. Supports PostgreSQL, sqlite3 (3.8.3 or higher) and MariaDB (10.2.2 or higher) and MySQL (8.0 or higher, if running without ONLY_FULL_GROUP_BY).

Supports Django 2.2 or better, Python 3.6 or better. See the GitHub actions build for more details.

Features and limitations

• Supports only integer primary keys.

• Allows specifying ordering among siblings.

• Uses the correct definition of depth, where root nodes have a depth of zero.

• The parent foreign key must be named "parent" at the moment (but why would you want to name it differently?)

• The fields added by the common table expression always are tree_depth, tree_path and tree_ordering. The names cannot be changed. tree_depth is an integer, tree_path an array of primary keys and tree_ordering an array of values used for ordering nodes within their siblings.

• Besides adding the fields mentioned above the package only adds queryset methods for filtering ancestors and descendants. Other features may be useful, but will not be added to the package just because it’s possible to do so.

• Little code, and relatively simple when compared to other tree management solutions for Django. No redundant values so the only way to end up with corrupt data is by introducing a loop in the tree structure (making it a graph). The TreeNode abstract model class has some protection against this.

• Supports only trees with max. 50 levels on MySQL/MariaDB, since those databases do not support arrays and require us to provide a maximum length for the tree_path and tree_ordering upfront.

Here’s a blog post offering some additional insight (hopefully) into the reasons for django-tree-queries’ existence.

Usage

• Install django-tree-queries using pip.

• Extend tree_queries.models.TreeNode or build your own queryset and/or manager using tree_queries.query.TreeQuerySet. The TreeNode abstract model already contains a parent foreign key for your convenience and also uses model validation to protect against loops.

• Call the with_tree_fields() queryset method if you require the additional fields respectively the CTE.

• Create a manager using TreeQuerySet.as_manager(with_tree_fields=True) if you want to add tree fields to queries by default.

• Until documentation is more complete I’ll have to refer you to the test suite for additional instructions and usage examples.