# List of notable changes made between 2.x and 3.0

All breaking changes must be described here. When adding a new entry,
always describe the impact on users and instructions for upgrading
applications from 2.x to 3.0.

## loopback-datasource-juggler was moved from peerDependencies to dependencies

Originally, we (ab)used peer dependencies to ensure there is only one instance
of loopback-datasource-juggler in the dependency tree, so that there is only
one singleton instance of model registry. This was very fragile and might not
have worked in certain edge cases.

We have reworked loopback-datasource-juggler and connectors to not rely on
a single juggler instance anymore. As the last step, juggler became a regular
dependency.

https://github.com/strongloop/loopback/issues/275

When upgrading application from previous loopback versions, simply remove
loopback-datasource-juggler from your dependencies.

## always use bluebird as promise library

In version 3.0, we always use bluebird as our promise library
instead of `global.Promise`.
We consider Bluebird API a part of LoopBack API from now on,
you are welcome to use any Bluebird-specific methods in your applications.

If you are using LoopBack with a custom promise implementation provided
via `global.Promise`,
you will have to check all places where you are using non-standard promise API
and update them to use Bluebird API instead.

Please see [Related code change](https://github.com/strongloop/loopback/pull/1896) here.

## new method of defining remoting metadata

In 2.0, remote methods were defined as:
```
methods: {
  staticMethod: {
    isStatic: true,
    http: { path: '/static' }
  },
  instanceMethod: {
    isStatic: false,
    http: { path: '/instance' }
  }
}
```

For 3.0, the isStatic flag is no longer required and will be determined from the method name.
Method name starting with "prototype." will be the same as having isStatic flag set to false.
```
methods: {
  staticMethod: {
    http: { path: '/static' }
  },
  'prototype.instanceMethod': {
  http: { path: '/instance' }
}
```

Please see [related code change](https://github.com/strongloop/loopback/pull/2174) here.

## remove `Change.handleError`
`Change.handleError` is now removed as it was used inconsistenly for a subset of possible
errors only. All Change methods will report all errors to the caller via the callback.

Use PersistedModel to report change-tracking errors via the existing method
PersistedModel.handleChangeError. This method can be customized on a per-model basis to
provide different error handling.

Please see [related code change](https://github.com/strongloop/loopback/pull/2308) here.


## remove unused user properties
The following properties are removed from the built-in User model in 3.0:
- credentials
- challenges
- status
- created
- lastUpdated

Developers that are relying on these properties, can redefine them in `user.json` or equivalent model.json as follow:
```json
{
  "name": "MyUser",
  "base": "User",
  "properties": {
    "credentials": { "type": "object" },
    "challenges": { "type": "object" },
    "status": "string",
    "created": "date",
    "lastUpdated": "date"
  }
}
```

Please see [Related code change](https://github.com/strongloop/loopback/pull/2299) here.

## Remove getters for Express 3.x middleware

Express 4.x stopped bundling commonly-used middleware. To simplify migration
of LoopBack 1.x applications (powered by Express 3.x) to LoopBack 2.x (powered
by Express 4.x), we created getter properties to allow developers to keep using
the old convention.

We have removed these getters in LoopBack 3.0, here is the full list of
removed properties together with the middleware module name to use instead:

 - `loopback.compress` - use `require('compression')` instead
 - `loopback.timeout` - use `require('connect-timeout')` instead
 - `loopback.cookieParser` - use `require('cookie-parser')` instead
 - `loopback.cookieSession` - use `require('cookie-session')` instead
 - `loopback.csrf` - use `require('csurf')` instead
 - `loopback.errorHandler` - use `require('errorhandler')` instead
 - `loopback.session` - use `require('express-session')` instead
 - `loopback.methodOverride` - use `require('method-override')` instead
 - `loopback.logger` - use `require('morgan')` instead
 - `loopback.responseTime` - use `require('response-time')` instead
 - `loopback.favicon` - use `require('serve-favicon')` instead
 - `loopback.directory` - use `require('serve-index')` instead
 - `loopback.vhost` - use `require('vhost')` instead

We have also removed `loopback.mime`, which was always set to `undefined`.

See [loopback#2349](https://github.com/strongloop/loopback/pull/2394).

## Remove `loopback#errorhandler`

We have removed `loopback#errorhandler` middleware, users should use `strong-error-handler` directly.

```js
// server/middleware.json
{
  // ...
  "final:after": {
    "strong-error-handler": {}
  }
}

// server/middleware.development.json
{
  "final:after": {
    "strong-error-handler": {
      "params": {
        "debug": true
      }
  }
}
```

See also strong-error-handler's [options](https://github.com/strongloop/strong-error-handler#options) and the [related code change](https://github.com/strongloop/loopback/pull/2411).

## Remove current context API and middleware

We have removed the following current-context-related APIs:

 - `loopback.getCurrentContext`
 - `loopback.createContext`
 - `loopback.runInContext`

Additionally, `loopback#context` middleware and `remoting.context` server
config were removed too.

#### Upgrading from 2.x to 3.x

When upgrading from LoopBack 2.x, you need to disable or remove
`remoting.context` configuration in your server config.

```js
{
  "remoting": {
    "context": false, // or remove completely
    // etc.
  },
  // etc.
}
```

Without this change, you will see the following error on the first HTTP request
received:

```
Unhandled error for request GET /api/Users:
Error: remoting.context option was removed in version 3.0.
See https://docs.strongloop.com/display/APIC/Using%20current%20context for more
details.
    at restApiHandler (.../node_modules/loopback/server/middleware/rest.js:44:15)
    at Layer.handle [as handle_request] (.../node_modules/express/lib/router/layer.js:95:5)
```

#### Setting up "current context" in 3.x

To setup "current context" feature in your LoopBack 3.x application, you
should use [loopback-context](https://www.npmjs.com/package/loopback-context)
module:

 1. Add `loopback-context` to your dependencies

 2. Configure the new context middleware in your `server/middleware-config.json` file
    ```json
    {
      "initial": {
        "loopback-context#per-request": {}
      }
    }
    ```

 3. Replace all usages of `loopback.getCurrentContext` with the following:
    ```js
    // at the top of your file
    var LoopBackContext = require('loopback-context');

    // in your code
    var ctx = LoopBackContext.getCurrentContext();
    if (ctx) {
      // use the context
    }
    ```

See also [loopback#2564](https://github.com/strongloop/loopback/pull/2564)
and the official [documentation](https://docs.strongloop.com/display/APIC/Using+current+context)

## Remove sugar for creating models

`app.model(modelName, settings)`, a sugar for creating non-existing model, is
now removed in favor of promoting use of:
- `app.registry.createModel(modelName, properties, options)` to create new model
- `app.model(modelCtor, config)` to update existing model and attach it to app

Please see [related code change](https://github.com/strongloop/loopback/pull/2401) here.