feat: add optional prefix parameter to nanoid() for typed ids #18

[nik-sta]

Summary

Adds prefix text DEFAULT '' as the new last parameter of nanoid(), prepended to the generated id for Stripe-style typed ids (usr_, ord_, ...):

• size keeps meaning the number of random symbols; the total id length is length(prefix) + size, so columns must be sized accordingly (e.g. char(25) for nanoid(prefix => 'usr_'))
• A NULL prefix behaves like an empty prefix instead of producing a NULL id (coalesce(prefix, ''))
• nanoid_optimized() stays unchanged; the prefix is concatenated in nanoid()
• The old signature nanoid(int, text, float) is dropped on upgrade, as the install script already does today
• README documents the parameter, the length semantics, and a CREATE TABLE example

Stacked on #24; the diff of this PR is the prefix commit only.

Verification

• Unit tests: positional prefix, named notation nanoid(prefix => 'ord_'), and NULL prefix; SELECT nanoid() behavior is unchanged (21 characters, default alphabet)
• Full multi-version suite passes on PostgreSQL 9.6 through 18
• Upgrade path verified: installing the new nanoid.sql over an existing installation leaves exactly one nanoid(size, alphabet, additionalBytesFactor, prefix) signature

Credits

Idea by @abdirahmn1.

Closes #18

Summary by CodeRabbit

• New Features

  • Added an optional prefix parameter to generated Nano IDs, supporting typed identifiers such as usr_ and ord_.
  • Prefixes are included in the final ID without reducing the requested random portion size.
  • Prefixes can be provided positionally or by name.

• Bug Fixes

  • A NULL prefix now behaves like no prefix (no longer yields a NULL identifier).

• Documentation

  • Expanded “Prefixed ids” with new SQL examples and clarifications on total ID length and NULL prefix behavior.

• Tests

  • Added unit coverage for prefix/size interactions, pattern expectations, and edge cases.

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⚙️ Run configuration

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📥 Commits

Reviewing files that changed from the base of the PR and between 681163e and b9c3b58.

📒 Files selected for processing (3)

• README.md
• dev/test/unit_tests.sql
• nanoid.sql

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📝 Walkthrough

Walkthrough

The nanoid function now accepts an optional prefix, prepends it to generated IDs, treats NULL as empty, and documents and tests the resulting length and format behavior.

Changes

Nanoid prefix support

Layer / File(s)	Summary
Prefix parameter and generation nanoid.sql	The nanoid signature adds an optional prefix parameter, removes older overloads, and prepends the NULL-safe prefix to the generated identifier.
Prefix validation and documentation dev/test/unit_tests.sql, README.md	Tests cover positional, named, mixed-notation, NULL, and multi-byte prefixes; README examples describe typed prefixes and total ID length.

Estimated code review effort: 2 (Simple) | ~10 minutes

🚥 Pre-merge checks | ✅ 5

✅ Passed checks (5 passed)

Check name	Status	Explanation
Description Check	✅ Passed	Check skipped - CodeRabbit’s high-level summary is enabled.
Title check	✅ Passed	The title clearly describes the main change: adding an optional prefix parameter to nanoid() for typed IDs.
Linked Issues check	✅ Passed	The changes implement the optional prefix, preserve size semantics, handle NULL as empty, keep nanoid_optimized() unchanged, add docs/tests, and drop the old signature.
Out of Scope Changes check	✅ Passed	The PR stays focused on the prefix feature, with only related docs, tests, and migration updates.
Docstring Coverage	✅ Passed	No functions found in the changed files to evaluate docstring coverage. Skipping docstring coverage check.

✨ Finishing Touches

🧪 Generate unit tests (beta)

• Create PR with unit tests
• Commit unit tests in branch feat/18-nanoid-prefix

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