neo4j-migration-skill

## When to Use
- Upgrading driver dependency from 4.x or 5.x to 6.x
- Migrating Cypher queries to Cypher 25 syntax
- Fixing deprecated API warnings after a driver or Neo4j version bump
- Auditing a codebase for removed/deprecated Neo4j APIs before upgrading

## When NOT to Use
- **Writing new Cypher queries** → `neo4j-cypher-skill`
- **DB admin** (backup, restore, import, cypher-shell) → `neo4j-cli-tools-skill`
- **Starting fresh** → `neo4j-getting-started-skill`
- **GDS algorithm migration** — not covered here; consult GDS release notes

---

## Entry Criteria

Before starting, ask:
1. **Target Neo4j version** — needed to select Cypher dialect and driver version
2. **Languages in use** — scan `package.json`, `requirements.txt`, `pom.xml`, `*.csproj`, `go.mod`
3. **Current driver versions** — read from dependency files; do NOT guess

If target is >= 2025.06: ask whether Cypher 5 or Cypher 25 dialect will be used (both supported; Cypher 25 is the new default).

---

## Step 1 — Scan Codebase

```bash
# Find Cypher strings (queries embedded in source)
grep -rn "MATCH\|MERGE\|CREATE\|CALL\|RETURN" --include="*.py" --include="*.js" \
  --include="*.ts" --include="*.java" --include="*.cs" --include="*.go" \
  --include="*.cypher" --include="*.cql" . | grep -v ".git"

# Find dependency files
find . -name "requirements*.txt" -o -name "package.json" -o -name "pom.xml" \
  -o -name "*.csproj" -o -name "go.mod" | grep -v ".git" | grep -v node_modules
```

Collect findings before modifying anything. List all deprecated patterns found.

---

## Step 2 — Cypher Migration (4.x / 5.x → Cypher 25)

Apply to every Cypher string, `.cypher` file, OGM/SDN `@Query` annotation, and template literal.

### Complete Substitution Table

| Old syntax | Cypher 25 replacement | Notes |
|---|---|---|
| `[:REL*1..5]` | `(()-[:REL]->()){1,5}` | QPE quantifier group |
| `[:REL*]` | `(()-[:REL]->()){1,}` | Unbounded QPE |
| `[:REL*0..5]` | `(()-[:REL]->()){0,5}` | Zero-hop allowed |
| `shortestPath((a)-[*]->(b))` | `SHORTEST 1 (a)(()-[]->()){1,}(b)` | QPE shortest path |
| `allShortestPaths((a)-[*]->(b))` | `ALL SHORTEST (a)(()-[]->()){1,}(b)` | QPE all-shortest |
| `id(n)` | `elementId(n)` | Returns string, not int |
| `CALL { WITH x ... }` | `CALL (x) { ... }` | Explicit import syntax |
| `PERIODIC COMMIT` | `CALL (...) { ... } IN TRANSACTIONS OF 1000 ROWS` | Batched writes |
| `-- comment` | `// comment` | SQL comment invalid |
| `SET n = r` (structural val) | `SET n = properties(r)` | Extract map first |
| `MERGE (a {x:1})-[:T]->(b {x:a.x})` | Rewrite — cross-entity MERGE refs disallowed | Split into MATCH+MERGE |
| `CREATE INDEX ... OPTIONS { indexProvider: ... }` | Remove `indexProvider` from OPTIONS | Provider selection removed |
| `db.create.setVectorProperty(...)` | Use native VECTOR property type | Procedure removed |
| `dbms.upgrade()` / `dbms.upgradeStatus()` | Use `cypher-shell :sysinfo` | Procedures removed |
| `USE composite.'1'` | `` USE `composite.1` `` | Backtick entire qualified name |
| `RETURN 1 as my$Identifier` | `` RETURN 1 as `my$Identifier` `` | `$` removed from unescaped ids |

### Vector Index Queries (version-branched)

| Version | Syntax |
|---|---|
| Neo4j < 2026.01 | `CALL db.index.vector.queryNodes(idx, k, $emb) YIELD node, score` |
| Neo4j >= 2026.01 | `SEARCH n IN (VECTOR INDEX idx FOR $emb LIMIT k) SCORE AS score` |

### Cypher Dialect Prefix Rule

- Target >= 2025.06, dialect = Cypher 25: prepend `CYPHER 25` to every top-level query
- Target >= 2025.06, dialect = Cypher 5: prepend `CYPHER 5` (keeps deprecated forms working)
- Target 4.x or 5.x: no prefix needed; fetch changelog per [references/cypher-queries.md](references/cypher-queries.md)

### `id(n)` → `elementId(n)` Caveats

`elementId()` returns a string (e.g., `"4:abc123:0"`), not an integer. Fix downstream code that stores or compares it as `int`. Do NOT use `elementId()` values for numeric operations.

```diff
- WHERE id(n) = $nodeId   # $nodeId was integer
+ WHERE elementId(n) = $nodeId  # $nodeId must now be string
```

---

## Step 3 — Driver Migration

Pick the section(s) matching languages found in Step 1.

---

### Python Driver (5.x → 6.x)

**Min requirements**: Python >= 3.10, `neo4j` package (6.0+, released Jan 12 2026)

#### Package Rename — do this first

```diff
# requirements.txt
- neo4j-driver>=5.0.0
+ neo4j>=6.0.0
```

`neo4j-driver` package is deprecated since 6.0 and receives no further updates.

#### Removed APIs

| Old | New | Notes |
|---|---|---|
| `session.read_transaction(fn)` | `session.execute_read(fn)` | |
| `session.write_transaction(fn)` | `session.execute_write(fn)` | |
| `session.last_bookmark()` | `session.last_bookmarks()` | Returns `Bookmarks` (plural) |
| `Bookmark` class | `Bookmarks` class | |
| `TRUST_ALL_CERTIFICATES` | `trusted_certificates=TrustAll()` | |
| `TRUST_SYSTEM_CA_SIGNED_CERTIFICATES` | `trusted_certificates=TrustSystemCAs()` | |
| `neo4j.conf`, `neo4j.data` modules | Removed — use top-level `neo4j.*` | |

#### Resource Management Change

Drivers and sessions no longer auto-close on GC. Add explicit cleanup:

```diff
- driver = GraphDatabase.driver(URI, auth=(USER, PASS))
- # used without explicit close
+ with GraphDatabase.driver(URI, auth=(USER, PASS)) as driver:
+     with driver.session(database="neo4j") as session:
+         ...
```

Or call `.close()` explicitly. Repeated `.close()` is a no-op.

#### Error Handling Changes

| Old exception | New exception | Trigger |
|---|---|---|
| `ClientError` (for timeout) | `ConnectionAcquisitionTimeoutError` | Acquisition timeout |
| `AuthError` (invalid config) | `ConfigurationError` | Invalid auth params |
| `ValueError` raised for `Query` obj | `TypeError` | Passing `Query` to `Transaction.run` |

#### Key APIs Unchanged

`execute_query()`, `GraphDatabase.driver()`, `neo4j+s://` URI, `auth=(user, pw)`, session `run()`.

Full changelog: [references/python-driver.md](references/python-driver.md)

---

### JavaScript / Node.js Dri