<!-- don't edit here, its from https://@github.com/arangodb/arangodbjs.git / docs/Drivers/ -->
# EdgeCollection API

The _EdgeCollection API_ extends the
[_Collection API_](README.md) with the following methods.

## edgeCollection.edge

`async edgeCollection.edge(documentHandle): Object`

Retrieves the edge with the given _documentHandle_ from the collection.

**Arguments**

* **documentHandle**: `string`

  The handle of the edge to retrieve. This can be either the `_id` or the `_key`
  of an edge in the collection, or an edge (i.e. an object with an `_id` or
  `_key` property).

**Examples**

```js
const db = new Database();
const collection = db.edgeCollection('edges');

const edge = await collection.edge('some-key');
// the edge exists
assert.equal(edge._key, 'some-key');
assert.equal(edge._id, 'edges/some-key');

// -- or --

const edge = await collection.edge('edges/some-key');
// the edge exists
assert.equal(edge._key, 'some-key');
assert.equal(edge._id, 'edges/some-key');
```

## edgeCollection.save

`async edgeCollection.save(data, [fromId, toId]): Object`

Creates a new edge between the documents _fromId_ and _toId_ with the given
_data_ and returns an object containing the edge's metadata.

**Arguments**

* **data**: `Object`

  The data of the new edge. If _fromId_ and _toId_ are not specified, the _data_
  needs to contain the properties `_from` and `_to`.

* **fromId**: `string` (optional)

  The handle of the start vertex of this edge. This can be either the `_id` of a
  document in the database, the `_key` of an edge in the collection, or a
  document (i.e. an object with an `_id` or `_key` property).

* **toId**: `string` (optional)

  The handle of the end vertex of this edge. This can be either the `_id` of a
  document in the database, the `_key` of an edge in the collection, or a
  document (i.e. an object with an `_id` or `_key` property).

* **opts**: `Object` (optional)

  If _opts_ is set, it must be an object with any of the following properties:

  * **waitForSync**: `boolean` (Default: `false`)

    Wait until document has been synced to disk.

  * **returnNew**: `boolean` (Default: `false`)

    If set to `true`, return additionally the complete new documents under the
    attribute `new` in the result.

  * **returnOld**: `boolean` (Default: `false`)

    If set to `true`, return additionally the complete old documents under the
    attribute `old` in the result.

  * **silent**: `boolean` (Default: `false`)

    If set to true, an empty object will be returned as response. No meta-data
    will be returned for the created document. This option can be used to save
    some network traffic.

  * **overwrite**: `boolean` (Default: `false`)

    If set to true, the insert becomes a replace-insert. If a document with the
    same _key already exists the new document is not rejected with unique
    constraint violated but will replace the old document.

If a boolean is passed instead of an options object, it will be interpreted as
the _returnNew_ option.

**Examples**

```js
const db = new Database();
const collection = db.edgeCollection('edges');
const data = {some: 'data'};

const info = await collection.save(
  data,
  'vertices/start-vertex',
  'vertices/end-vertex'
);
assert.equal(info._id, 'edges/' + info._key);
const edge = await collection.edge(edge)
assert.equal(edge._key, info._key);
assert.equal(edge._rev, info._rev);
assert.equal(edge.some, data.some);
assert.equal(edge._from, 'vertices/start-vertex');
assert.equal(edge._to, 'vertices/end-vertex');

// -- or --

const info = await collection.save({
  some: 'data',
  _from: 'verticies/start-vertex',
  _to: 'vertices/end-vertex'
});
// ...
```

## edgeCollection.edges

`async edgeCollection.edges(documentHandle): Array<Object>`

Retrieves a list of all edges of the document with the given _documentHandle_.

**Arguments**

* **documentHandle**: `string`

  The handle of the document to retrieve the edges of. This can be either the
  `_id` of a document in the database, the `_key` of an edge in the collection,
  or a document (i.e. an object with an `_id` or `_key` property).

**Examples**

```js
const db = new Database();
const collection = db.edgeCollection('edges');
await collection.import([
  ['_key', '_from', '_to'],
  ['x', 'vertices/a', 'vertices/b'],
  ['y', 'vertices/a', 'vertices/c'],
  ['z', 'vertices/d', 'vertices/a']
])
const edges = await collection.edges('vertices/a');
assert.equal(edges.length, 3);
assert.deepEqual(edges.map(edge => edge._key), ['x', 'y', 'z']);
```

## edgeCollection.inEdges

`async edgeCollection.inEdges(documentHandle): Array<Object>`

Retrieves a list of all incoming edges of the document with the given
_documentHandle_.

**Arguments**

* **documentHandle**: `string`

  The handle of the document to retrieve the edges of. This can be either the
  `_id` of a document in the database, the `_key` of an edge in the collection,
  or a document (i.e. an object with an `_id` or `_key` property).

**Examples**

```js
const db = new Database();
const collection = db.edgeCollection('edges');
await collection.import([
  ['_key', '_from', '_to'],
  ['x', 'vertices/a', 'vertices/b'],
  ['y', 'vertices/a', 'vertices/c'],
  ['z', 'vertices/d', 'vertices/a']
]);
const edges = await collection.inEdges('vertices/a');
assert.equal(edges.length, 1);
assert.equal(edges[0]._key, 'z');
```

## edgeCollection.outEdges

`async edgeCollection.outEdges(documentHandle): Array<Object>`

Retrieves a list of all outgoing edges of the document with the given
_documentHandle_.

**Arguments**

* **documentHandle**: `string`

  The handle of the document to retrieve the edges of. This can be either the
  `_id` of a document in the database, the `_key` of an edge in the collection,
  or a document (i.e. an object with an `_id` or `_key` property).

**Examples**

```js
const db = new Database();
const collection = db.edgeCollection('edges');
await collection.import([
  ['_key', '_from', '_to'],
  ['x', 'vertices/a', 'vertices/b'],
  ['y', 'vertices/a', 'vertices/c'],
  ['z', 'vertices/d', 'vertices/a']
]);
const edges = await collection.outEdges('vertices/a');
assert.equal(edges.length, 2);
assert.deepEqual(edges.map(edge => edge._key), ['x', 'y']);
```

## edgeCollection.traversal

`async edgeCollection.traversal(startVertex, opts): Object`

Performs a traversal starting from the given _startVertex_ and following edges
contained in this edge collection.

**Arguments**

* **startVertex**: `string`

  The handle of the start vertex. This can be either the `_id` of a document in
  the database, the `_key` of an edge in the collection, or a document (i.e. an
  object with an `_id` or `_key` property).

* **opts**: `Object`

  See
  [the HTTP API documentation](../../../..//HTTP/Traversal/index.html)
  for details on the additional arguments.

  Please note that while _opts.filter_, _opts.visitor_, _opts.init_,
  _opts.expander_ and _opts.sort_ should be strings evaluating to well-formed
  JavaScript code, it's not possible to pass in JavaScript functions directly
  because the code needs to be evaluated on the server and will be transmitted
  in plain text.

**Examples**

```js
const db = new Database();
const collection = db.edgeCollection('edges');
await collection.import([
  ['_key', '_from', '_to'],
  ['x', 'vertices/a', 'vertices/b'],
  ['y', 'vertices/b', 'vertices/c'],
  ['z', 'vertices/c', 'vertices/d']
]);
const result = await collection.traversal('vertices/a', {
  direction: 'outbound',
  visitor: 'result.vertices.push(vertex._key);',
  init: 'result.vertices = [];'
});
assert.deepEqual(result.vertices, ['a', 'b', 'c', 'd']);
```