Question 1

How do I migrate from acts_as_nested_set to ancestry in Rails?

Accepted Answer

First, install ancestry and remove the old gem, then use the built-in migration tool by running 'Model.build_ancestry_from_parent_ids!' in the console to populate the ancestry column from existing parent IDs. After verifying integrity with 'check_ancestry_integrity!', remove the old parent_id column via a migration.

Question 2

What's the difference between ancestry and closure_tree for hierarchical data?

Accepted Answer

Ancestry uses a materialized path stored in a single column for fast reads and simple setup, while closure_tree uses a separate closure table for more flexible writes and complex queries. Ancestry is better for read-heavy Rails apps, whereas closure_tree might suit write-intensive scenarios.

Question 3

How can I limit the depth of a tree using ancestry gem?

Accepted Answer

Enable depth caching with 'has_ancestry cache_depth: true', then add a Rails validation on the depth column, such as 'validates :ancestry_depth, numericality: { less_than_or_equal_to: 5 }'. Ancestry will automatically validate depth during moves to prevent exceeding limits.

Question 4

Does ancestry work with UUIDs as primary keys?

Accepted Answer

Yes, ancestry supports UUIDs by setting 'primary_key_format: :uuid' in the 'has_ancestry' options. This ensures the ancestry column correctly handles UUID strings in the path format, though it may affect performance due to longer strings.

Question 5

What happens to child nodes when I delete a parent with ancestry?

Accepted Answer

Ancestry provides multiple orphan strategies configurable via 'orphan_strategy': :destroy (default) deletes children, :rootify makes them root nodes, :restrict raises an error, or :adopt attaches them to the grandparent. Choose based on your data integrity needs.

Question 6

How to use PostgreSQL ltree with ancestry for better indexing?

Accepted Answer

Set 'ancestry_format: :ltree' in your migration and model, and enable the ltree extension in PostgreSQL. This allows native GiST indexing and avoids string parsing, but it's PostgreSQL-only and requires specific database setup.

Ancestry

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