From 2f2451c0d36e33183217e7689f5c25748a6fefb5 Mon Sep 17 00:00:00 2001
From: "claude[bot]" <209825114+claude[bot]@users.noreply.github.com>
Date: Mon, 31 Aug 2026 02:08:22 +0000
Subject: [PATCH] =?UTF-8?q?docs(skills):=20$exists=20means=20HAS=20A=20VAL?=
 =?UTF-8?q?UE=20=E2=80=94=20retire=20the=20MongoDB=20$exists=20claim=20(#1?=
 =?UTF-8?q?3539)?=
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GOVERNED SURFACE — published, customer-facing skill text.

Both rows taught key-presence, and `objectstack-query/SKILL.md` named the
mapping outright: "MongoDB `$exists`". Since 9dac1ae017 (PR #13529)
`driver-mongodb`'s translateFilter never emits MongoDB's `$exists` — it lowers
the operator to `{$ne: null}` / `{$eq: null}` — so a customer following that
line writes a filter whose behaviour differs from the promise on any
null-valued field.

Established from code and from an executed test, not from another document:

- mongodb-filter.ts `case '$exists'` puts `$ne: null` / `$eq: null`;
- sql-driver.ts `case '$exists'` compiles whereNotNull / whereNull;
- objectql having-filter.ts evaluates `value !== undefined && value !== null`;
- 14/14 green in driver-mongodb/src/mongodb-exists-has-value-translation.test.ts,
  which pins `translateFilter({name: {$exists: true}})` to `{name: {$ne: null}}`.

Written to the published token ratchet rather than around it: both files carry
zero headroom, so the correction is byte-neutral-or-shrinking rather than an
added warning. SKILL.md 22208 -> 22207 bytes, filters.md 8593 -> 8596; both
files unchanged in tokens and lines, bundle total unchanged at 186751.

Co-Authored-By: Claude Opus 5 <noreply@anthropic.com>
Claude-Session: https://claude.ai/code/session_01Pk26oZ12t5N1hwGW1m1MgC
---
 skills/objectstack-query/SKILL.md         | 2 +-
 skills/objectstack-query/rules/filters.md | 2 +-
 2 files changed, 2 insertions(+), 2 deletions(-)

diff --git a/skills/objectstack-query/SKILL.md b/skills/objectstack-query/SKILL.md
index f68b4f46b1..34e0d0142d 100644
--- a/skills/objectstack-query/SKILL.md
+++ b/skills/objectstack-query/SKILL.md
@@ -154,7 +154,7 @@ The simplest filter — field equals value:
 | Operator | Purpose | SQL / NoSQL |
 |:---------|:--------|:------------|
 | `$null` | Is null check | `IS NULL` / `IS NOT NULL` |
-| `$exists` | Field exists (NoSQL) | MongoDB `$exists` |
+| `$exists` | Has a value | `IS NOT NULL` / `IS NULL` |
 
 ```typescript
 { where: { deleted_at: { $null: true } } }
diff --git a/skills/objectstack-query/rules/filters.md b/skills/objectstack-query/rules/filters.md
index 08c6b428a5..30db6c49a7 100644
--- a/skills/objectstack-query/rules/filters.md
+++ b/skills/objectstack-query/rules/filters.md
@@ -20,7 +20,7 @@ Comprehensive guide for building ObjectStack query filters.
 | String | `$startsWith` | `LIKE ?%` | `{ code: { $startsWith: 'PRJ-' } }` |
 | String | `$endsWith` | `LIKE %?` | `{ file: { $endsWith: '.pdf' } }` |
 | Null | `$null` | `IS NULL` / `IS NOT NULL` | `{ deleted_at: { $null: true } }` |
-| Existence | `$exists` | (NoSQL) `$exists` | `{ metadata: { $exists: true } }` |
+| Null | `$exists` | `IS NOT NULL` / `IS NULL` | `{ metadata: { $exists: true } }` |
 
 ## Implicit Equality (Shorthand)