arangodb/Documentation/Books/Users/Upgrading/UpgradingChanges26.mdpp

!CHAPTER Incompatible changes in ArangoDB 2.6

It is recommended to check the following list of incompatible changes **before** 
upgrading to ArangoDB 2.6, and adjust any client programs if necessary.


!SECTION Changed behavior

!SUBSECTION AQL Graphs

In 2.6 the graph functions did undergo a performance lifting.
During this process we had to adopt the result format and the options for some of them.
In general all graph functions now have an option `includeData` which allows to trigger
if the result of this function should contain fully extracted documents `includeData: true`
or only the `_id` values `includeData: false`.
In most use cases the `_id` is sufficient to continue and the extraction of data is an unnecessary
operation.
Furthermore the result `SHORTEST_PATH` has changed. The old format returned a list of all vertices on the path.
Optionally it could include each sub-path for these vertices.
All of the documents were fully extracted.
Example:
```
[
  {
    vertex: {
      _id: "vertex/1",
      _key: "1",
      _rev: "1234"
      name: "Alice"
    },
    path: {
      vertices: [
        {
          _id: "vertex/1",
          _key: "1",
          _rev: "1234"
          name: "Alice"
        }
      ],
      edges: []
    }
  },
  {
    vertex: {
      _id: "vertex/2",
      _key: "2",
      _rev: "5678"
      name: "Bob"
    },
    path: {
      vertices: [
        {
          _id: "vertex/1",
          _key: "1",
          _rev: "1234"
          name: "Alice"
        }, {
          _id: "vertex/2",
          _key: "2",
          _rev: "5678"
          name: "Bob"
        }
      ],
      edges: [
        {
          _id: "edge/1",
          _key: "1",
          _rev: "9876",
          type: "loves"
        }
      ]
    }
  }
]
```

The new version is more compact.
Each `SHORTEST_PATH` will only return one document having the attributes `vertices`, `edges`, `distance`.
The `distance` is computed taking into account the given weight.
Optionally the documents can be extracted with `includeData: true`
Example:
```
{
  vertices: [
    "vertex/1",
    "vertex/2"
  ],
  edges: [
    "edge/1"
  ],
  distance: 1
}
```

The next function that returns a different format is `NEIGHBORS`.
Since 2.5 it returned an object with `edge` and `vertex` for each connected edge.
Example:
```
[
  {
    vertex: {
      _id: "vertex/2",
      _key: "2",
      _rev: "5678"
      name: "Bob"
    },
    edge: {
      _id: "edge/1",
      _key: "1",
      _rev: "9876",
      type: "loves"
    }
  } 
]
```
With 2.6 it will only return the vertex directly, again using `includeData: true`.
By default it will return a distinct set of neighbors, using the option `distinct: false` will include the same vertex for each edge pointing to it.
Example:
```
[
  "vertex/2"
]
```

!SUBSECTION V8

The V8 version shipped with ArangoDB was upgraded from 3.29.59 to 3.31.74.1.
This leads to additional ECMAScript 6 (ES6 or "harmony") features being enabled by 
default in ArangoDB's scripting environment.

Apart from that, a change in the interpretation of command-line options by V8 may
affect users. ArangoDB passes the value of the command-line option `--javascript.v8-options`
to V8 and leaves interpretation of the contents to V8. For example, the ArangoDB option
`--javascript.v8-options="--harmony"` could be used to tell V8 to enable its harmony 
features.

In ArangoDB 2.4, the following harmony options were made available by V8:

* --harmony_scoping (enable harmony block scoping)
* --harmony_modules (enable harmony modules (implies block scoping))
* --harmony_proxies (enable harmony proxies)
* --harmony_generators (enable harmony generators)
* --harmony_numeric_literals (enable harmony numeric literals (0o77, 0b11))
* --harmony_strings (enable harmony string)
* --harmony_arrays (enable harmony arrays)
* --harmony_arrow_functions (enable harmony arrow functions)
* --harmony_classes (enable harmony classes)
* --harmony_object_literals (enable harmony object literal extensions)
* --harmony (enable all harmony features (except proxies))

There was the option `--harmony`, which turned on almost all harmony features.

In ArangoDB 2.5, V8 provides the following harmony-related options:
  
* --harmony (enable all completed harmony features)
* --harmony_shipping (enable all shipped harmony fetaures)
* --harmony_modules (enable "harmony modules (implies block scoping)" (in progress))
* --harmony_arrays (enable "harmony array methods" (in progress))
* --harmony_array_includes (enable "harmony Array.prototype.includes" (in progress))
* --harmony_regexps (enable "harmony regular expression extensions" (in progress))
* --harmony_arrow_functions (enable "harmony arrow functions" (in progress))
* --harmony_proxies (enable "harmony proxies" (in progress))
* --harmony_sloppy (enable "harmony features in sloppy mode" (in progress))
* --harmony_unicode (enable "harmony unicode escapes" (in progress))
* --harmony_tostring (enable "harmony toString")
* --harmony_numeric_literals (enable "harmony numeric literals")
* --harmony_strings (enable "harmony string methods")
* --harmony_scoping (enable "harmony block scoping")
* --harmony_classes (enable "harmony classes (implies block scoping & object literal extension)")
* --harmony_object_literals (enable "harmony object literal extensions")
* --harmony_templates (enable "harmony template literals")

Note that there are extra options for better controlling the dedicated features,
and especially that the meaning of the `--harmony` option has changed from enabling
**all** harmony features to **all completed** harmony features!

Users should adjust the value of `--javascript.v8-options` accordingly.

Please note that incomplete harmony features are subject to change in future V8 releases.