neo4j-import-skill

# Neo4j Import Skill

## When to Use

- Importing CSV, JSON, or Parquet files into Neo4j
- Batch-upserting nodes and relationships (UNWIND + CALL IN TRANSACTIONS)
- Migrating relational data (SQL → graph)
- Bulk-loading large datasets offline (neo4j-admin import)
- Choosing between online (Cypher) and offline (admin) import methods
- Verifying import completeness (counts, constraints, index states)

## When NOT to Use

- **Unstructured docs, PDFs, vector chunks** → `neo4j-document-import-skill`
- **Live application writes (MERGE/CREATE in app code)** → `neo4j-cypher-skill`
- **neo4j-admin backup/restore/config** → `neo4j-cli-tools-skill`
- **GDS algorithm projection from existing graph** → `neo4j-gds-skill`

---

## Method Decision Table

| Dataset size | DB state | Source | Method |
|---|---|---|---|
| Any size | Online | CSV (Aura or local) | LOAD CSV + CALL IN TRANSACTIONS |
| < 1M rows | Online | List/API response | UNWIND + CALL IN TRANSACTIONS |
| > 10M rows | **Offline** (local/self-managed) | CSV / Parquet | `neo4j-admin database import full` |
| Any size | Online | APOC available | `apoc.periodic.iterate` + `apoc.load.csv` |
| Any size | Online | JSON/API | `apoc.load.json` or driver batching |
| Incremental delta | Offline (Enterprise) | CSV | `neo4j-admin database import incremental` |

**Aura**: only `https://` URLs — no `file:///`. Use neo4j-admin import only on self-managed.

---

## Pre-Import Checklist

Run in this exact order — skipping causes hard-to-debug duplicates or missed index usage:

**Constraints BEFORE import. Additional indexes AFTER import.**
- Constraints create implicit RANGE indexes used by MERGE during load + enforce uniqueness
- Additional non-unique indexes (TEXT, RANGE on non-key props, FULLTEXT) created after load — Neo4j populates them async from the committed data; poll `populationPercent` until 100%
- Creating extra indexes before import slows every write during load with no benefit

1. **Create uniqueness constraints** (enables index used by MERGE):
   ```cypher
   CREATE CONSTRAINT IF NOT EXISTS FOR (n:Person) REQUIRE n.id IS UNIQUE;
   CREATE CONSTRAINT IF NOT EXISTS FOR (n:Movie)  REQUIRE n.movieId IS UNIQUE;
   ```
   > **Neo4j 2026.02+ (Enterprise/Aura) — PREVIEW:** `ALTER CURRENT GRAPH TYPE SET { … }` can replace all individual constraint statements with a single declarative block. See `neo4j-cypher-skill/references/graph-type.md`. Use individual `CREATE CONSTRAINT` on older versions or Community Edition.

2. **Verify APOC if using apoc.* procedures**:
   ```cypher
   RETURN apoc.version();
   ```
   If fails → APOC not installed. Use plain LOAD CSV instead.

3. **Confirm target is PRIMARY** (not replica):
   ```cypher
   CALL dbms.cluster.role() YIELD role RETURN role;
   ```
   If role ≠ `PRIMARY` → stop. Redirect write to PRIMARY endpoint.

4. **Count source file rows** before import (catch encoding issues early):
   ```bash
   wc -l data/persons.csv    # Linux/macOS
   ```

5. **Verify UTF-8 encoding** — LOAD CSV requires UTF-8. Re-encode if needed:
   ```bash
   file -i persons.csv       # Check encoding
   iconv -f latin1 -t utf-8 persons.csv > persons_utf8.csv
   ```

---

## LOAD CSV Patterns

### Basic node import with type coercion and null handling

```cypher
CYPHER 25
LOAD CSV WITH HEADERS FROM 'file:///persons.csv' AS row
CALL (row) {
  MERGE (p:Person {id: row.id})
  ON CREATE SET
    p.name       = row.name,
    p.age        = toIntegerOrNull(row.age),
    p.score      = toFloatOrNull(row.score),
    p.active     = toBoolean(row.active),
    p.born       = CASE WHEN row.born IS NOT NULL AND row.born <> '' THEN date(row.born) ELSE null END,
    p.createdAt  = datetime()
  ON MATCH SET
    p.updatedAt  = datetime()
} IN TRANSACTIONS OF 10000 ROWS
  ON ERROR CONTINUE
  REPORT STATUS AS s
RETURN s.transactionId, s.committed, s.errorMessage
```

Null/empty-string rules:
- CSV missing column → `null` (safe)
- CSV empty string `""` → stored as `""` **not** `null` — use `nullIf(row.x, '')` to convert
- `toInteger(null)` throws → always use `toIntegerOrNull()`
- `toFloat(null)` throws → always use `toFloatOrNull()`
- Neo4j never stores `null` properties — they are silently dropped on SET

### Relationship import (nodes must exist first)

```cypher
CYPHER 25
LOAD CSV WITH HEADERS FROM 'file:///knows.csv' AS row
CALL (row) {
  MATCH (a:Person {id: row.fromId})
  MATCH (b:Person {id: row.toId})
  MERGE (a)-[:KNOWS {since: toIntegerOrNull(row.year)}]->(b)
} IN TRANSACTIONS OF 5000 ROWS
  ON ERROR CONTINUE
  REPORT STATUS AS s
```

Always import ALL nodes before ANY relationships — MATCH fails on missing nodes.

### Tab-separated or custom delimiter

```cypher
CYPHER 25
LOAD CSV WITH HEADERS FROM 'file:///data.tsv' AS row FIELDTERMINATOR '\t'
CALL (row) { MERGE (p:Person {id: row.id}) }
IN TRANSACTIONS OF 10000 ROWS ON ERROR CONTINUE
```

### Compressed files (ZIP / gzip — local files only)

```cypher
LOAD CSV WITH HEADERS FROM 'file:///archive.csv.gz' AS row ...
```

### Cloud storage (Enterprise Edition)

| Scheme | Example |
|---|---|
| AWS S3 | `s3://my-bucket/data/persons.csv` |
| Google Cloud Storage | `gs://my-bucket/persons.csv` |
| Azure Blob | `azb://account/container/persons.csv` |

### Useful built-in functions inside LOAD CSV

```cypher
linenumber()   // current line number — use as fallback ID
file()         // absolute path of file being loaded
```

---

## CALL IN TRANSACTIONS — Full Reference

### Syntax

```cypher
CALL (row) {
  // write logic
} IN [n CONCURRENT] TRANSACTIONS
  [OF batchSize ROW[S]]
  [ON ERROR {CONTINUE | BREAK | FAIL | RETRY [FOR duration SECONDS] [THEN {CONTINUE|BREAK|FAIL}]}]
  [REPORT STATUS AS statusVar]
```

### ON ERROR modes

| Mode | Behavior | Use when |
|---|---|---|
| `ON ERROR FAIL` | Default. Rolls back entire outer tx on first error | All-or-nothing strict import |
| `ON ERROR CONTINUE` | Skips failed batch, continues remaining batches | Resilient bulk load — track errors via REPORT STATUS