# Clotho

A Java OGM (Object-Graph Mapper) for ArcadeDB, built on Apache TinkerPop/Gremlin.

Clotho is not a 1:1 node-to-object mapper. A "Clotho object" is a subgraph — a root vertex
plus a declared set of edges and adjacent vertices spanning any number of hops. Complex graph
traversals and analytics remain the developer's responsibility, written via `@Query` on
repository interfaces. Clotho handles bounded object loading and persistence.

---

## Module Structure

```
clotho/
  clotho-core/              # Zero Spring dependency. All mapping logic.
  clotho-spring-boot-starter/ # Autoconfigure, @Transactional bridge, Spring beans.
  clotho-dev-app/           # Minimal Spring Boot app for development testing against
                            # a live ArcadeDB instance. Not a production artifact.
```

---

## Three Tiers of Graph-to-Java Mapping

### 1. Vertex Type
A single ArcadeDB vertex mapped to a Java class. Must extend `ClothoVertex`.

```java
@VertexType("Employee")
public class Employee extends ClothoVertex {
    @Property("name") String name;

    @Include @Via("HAS_ADDRESS")
    Address address;  // eagerly loaded as part of this object's boundary
}
```

### 2. Edge Type
A single ArcadeDB edge mapped to a Java class. Must extend `ClothoEdge`.

```java
@EdgeType("WORKS_AT")
public class WorksAt extends ClothoEdge {
    @OutVertex Employee employee;
    @InVertex Company company;  // omit @InVertex for edge-only inclusion
    LocalDate startDate;
}
```

### 3. Subgraph Type
A composite Java class assembled from multiple vertices and edges via a `@Query` traversal.
Has no ARID. Does NOT extend `ClothoVertex` or `ClothoEdge`.
`save()` delegates to all component `ClothoEntity` fields individually.

```java
@SubgraphType
public class EmployeeProfile {
    Employee employee;      // field name matches Gremlin as("employee")
    Manager manager;
    @Alias("dept") Department department;
}
```

---

## Technology Stack

| Concern | Library |
|---|---|
| Language | Java 21 |
| Build | Maven (multi-module) |
| Graph connection | Apache TinkerPop 3.x — `DriverRemoteConnection` over WebSocket |
| Null safety | JSpecify (`org.jspecify.annotations`) |
| Boilerplate reduction | Lombok |
| Testing | JUnit 5 |
| Spring integration | Spring Boot 3.x autoconfigure |

---

## Key Design Decisions

- **Schema-first**: Clotho assumes the ArcadeDB schema already exists. No DDL generation.
  The developer manages the schema (e.g., using a Flyway-based migration tool).
- **Optional lazy loading**: `@Include` fields default to `FetchType.EAGER` (always loaded).
  Declare `@Include(fetchType = FetchType.LAZY)` to skip a field during `populate()`. Lazy
  fields remain `null`/empty until the developer calls `session.loadField(vertex, "fieldName")`
  explicitly. No proxy or bytecode enhancement is used.
- **Single-query boundary loading**: All `@Include` fields for a vertex are fetched in a single
  Gremlin `project()` traversal. This eliminates N+1 queries per object boundary and prevents
  race conditions from sequential round-trips. For nested boundaries, each vertex gets its own
  single-project query (one query per vertex, not one per field).
- **Dirty tracking**: `ClothoEntity` tracks which fields were mutated via `notifyFieldChanged()`
  (called from manual setters). On save, `NEW` entities write all `@Property` fields; `MANAGED`
  entities write only dirty fields and skip the update entirely if nothing changed.
  `ClothoSession.close()` auto-saves all MANAGED entities (vertices and edges) that carry dirty fields.
- **Optimistic locking**: Declare `@Version Long version` on an entity field. Clotho reads
  ArcadeDB's built-in `@version` property on load and includes a `.has("@version", version)`
  filter on every update. A version mismatch throws `OptimisticLockException`. Both vertices
  and edges support `@Version`.
- **Edges are first-class citizens**: `ClothoEdge` entities participate in the same
  `EntityState` lifecycle, dirty tracking, `@Version` OCC, identity map caching, and
  auto-save-on-close as `ClothoVertex` entities. Edges can be loaded by ID via
  `session.load(EdgeType.class, id)`.
- **Result mapping**: Clotho always instantiates the most specific registered class matching
  the vertex/edge label. Declared return types are upper bounds only.
- **Inheritance**: Java class hierarchy is the primary mechanism. `additionalParents` on
  `@VertexType` handles ArcadeDB's multi-parent (diamond) inheritance where Java's single
  inheritance is insufficient.
- **No automatic deletion**: Removing an element from an `@Include` collection does not
  delete it from the graph. Call `session.delete()` explicitly.

See `docs/` for detailed specifications.

---

## Package Structure

```
com.binarygolem.clotho
  .core
    .model       # ClothoEntity, ClothoVertex, ClothoEdge, ARID
    .annotation  # All annotations (@VertexType, @EdgeType, @SubgraphType, etc.)
    .session     # ClothoSession, ClothoSessionFactory
    .registry    # TypeRegistry
    .mapping     # ObjectMapper, SubgraphLoader, SubgraphPersistor, SubgraphTypeAssembler
    .query       # QueryExecutor, @Query proxy infrastructure
    .exception   # UnknownTypeException, ClothoException hierarchy
  .spring
    .config      # ClothoAutoConfiguration
    .tx          # Transaction bridge
```

---

## Coding Conventions

### Nullability
Every parameter, return type, and field must carry `@NonNull` or `@Nullable` from JSpecify.
Default assumption is `@NonNull`; annotate only what can be null.

```java
import org.jspecify.annotations.NonNull;
import org.jspecify.annotations.Nullable;
```

### Lombok
Use Lombok where it reduces noise without obscuring intent:
- `@Getter` on domain classes
- `@Builder` on factory/config classes
- `@RequiredArgsConstructor` / `@AllArgsConstructor` on service classes
- `@Value` is NOT compatible with Clotho-managed domain objects (requires mutable fields)

**`@Setter` restriction on entity classes:** Do NOT use Lombok `@Setter` on any field
annotated with `@Property`, `@Include`, `@OutVertex`, `@InVertex`, or `@Version` on a
`ClothoVertex` or `ClothoEdge` subclass. Write a manual setter that calls
`notifyFieldChanged(fieldName)` so the session can track the change:

```java
// Correct
public void setName(String name) {
    this.name = name;
    notifyFieldChanged("name");
}

// Wrong — dirty tracking does not fire
@Setter String name;
```

Lombok `@Setter` remains allowed only for framework-managed fields (`id`, `outVertexId`,
`inVertexId`) because Clotho sets those itself and they are not part of dirty tracking.

### Comments
Write no comments unless the WHY is non-obvious. One line maximum.
Never write doc comments that restate what the method name already says.

### Naming
- ArcadeDB type names (labels) use the `@VertexType` / `@EdgeType` annotation value.
  Class names need not match label names exactly.
- Edge label constants: define as `public static final String LABEL = "WORKS_AT"` on the
  edge class to avoid magic strings at call sites.

---

## Development Setup

### Prerequisites
- Java 21
- Maven 3.9+
- A running ArcadeDB instance (for integration tests and `clotho-dev-app`)

### Build
```bash
mvn clean install
```

### Run `clotho-dev-app`
```bash
mvn -pl clotho-dev-app spring-boot:run
```

### Connection (local ArcadeDB default)
```properties
clotho.gremlin.url=ws://localhost:8182/gremlin
clotho.gremlin.username=root
clotho.gremlin.password=playwithdata
clotho.gremlin.traversal-source=g
```

---

## Implementation Status

| Phase | Description | Status |
|---|---|---|
| 1 | Project housekeeping — parent POM, module scaffold, package rename | Done |
| 2 | Base types and annotations — `ARID`, `ClothoEntity`, `ClothoVertex`, `ClothoEdge`, all annotations, exception hierarchy | Done |
| 3 | `clotho-dev-app` — Gremlin connection wiring, smoke test against live ArcadeDB | Done |
| 4 | `TypeRegistry` — classpath scan, label→class map, hierarchy inference, `additionalParents`/`parentLabel` | Done |
| 5 | `ElementMapper` — Gremlin `Vertex`/`Edge` → Java; always most-specific class by label | Done |
| 6 | `SubgraphLoader` — traverse `@Include`/`@Via`, multi-hop, cycle detection, edge-only; `SubgraphTypeAssembler` | Done |
| 7 | `SubgraphPersistor` — upsert, `@version` optimistic locking, cascade through boundary | Done |
| 8 | `ClothoSession` / `ClothoSessionFactory` — identity map, `load`/`save`/`delete`/`query`, connection lifecycle | Done |
| 9 | `ClothoRepository<T>` — abstract base class; `g()`, `execute()`, `findAll()`, `findById()`, etc.; dropped `@Query`/`@Param` | Done |
| 10 | Spring Boot Starter — `ClothoAutoConfiguration`, `ClothoProperties`, `@ClothoRepository` bean scanning | Done |
| 11 | Dirty tracking (`notifyFieldChanged`, `EntityState`), `SessionContext`, single-query `project()` loading, `@Version` OCC, `FetchType.LAZY`, `FieldMetadataCache`, expanded type coercion, `populateAll()` batch loading, auto-save on close, edge first-class parity | Done |
| 12 | Transaction management — `openTransactionalSession()`, borrow counter, `rollback()`, `getCurrentSession()`, `ClothoTransactionManager`, Spring `@Transactional` bridge, `ClothoAutoConfiguration` tx bean | Done |

---

## Documentation Index

| Document | Contents |
|---|---|
| `docs/TYPE_SYSTEM.md` | `ClothoEntity` hierarchy, `@VertexType`, `@EdgeType`, `@SubgraphType`, inheritance, diamond inheritance, result mapping rule |
| `docs/OBJECT_BOUNDARY.md` | `@Include`/`@Via`, multi-hop traversal, edge-only inclusion, cycle detection |
| `docs/ANNOTATIONS.md` | Complete annotation reference with all attributes and examples |
| `docs/QUERY_MODEL.md` | `@Query`, `@ClothoRepository`, `@SubgraphType` assembly, result mapping, parameter binding |
| `docs/SPRING_INTEGRATION.md` | Autoconfigure, `@Transactional`, `application.properties` reference |
| `docs/ARCHITECTURE.md` | Module breakdown, key components, data flow, session lifecycle |
| `docs/TRANSACTIONS.md` | Transactional sessions, Spring `@Transactional`, nested propagation, `@Version` interaction, limitations |