fix: migrate LB3 models mounted on LB4 app

Migrates LB4 models mounted on LB4 an app.

packages/booter-lb3app/fixtures/app-with-model.js

@@ -0,0 +1,18 @@
+'use strict';
+
+const loopback = require('loopback');
+const boot = require('loopback-boot');
+
+const app = (module.exports = loopback());
+
+app.dataSource('memory', {connector: 'memory'});
+const Color = app.registry.createModel('Color', {name: String});
+app.model(Color, {dataSource: 'memory'});
+
+app.get('/hello', (req, res) => {
+  res.send('hello');
+});
+
+boot(app, __dirname, function(err) {
+  if (err) throw err;
+});

packages/booter-lb3app/src/__tests__/acceptance/booter-lb3app.acceptance.ts

@@ -3,7 +3,7 @@
 // This file is licensed under the MIT License.
 // License text available at https://opensource.org/licenses/MIT
 
-import {OperationObject, OpenApiSpec} from '@loopback/rest';
+import {OpenApiSpec, OperationObject} from '@loopback/rest';
 import {Client, expect} from '@loopback/testlab';
 import * as _ from 'lodash';
 import {
@@ -215,4 +215,21 @@ describe('booter-lb3app', () => {
       expect(createOp.summary).to.eql('just a very simple modification');
     });
   });
+
+  context('binding LoopBack 3 datasources', () => {
+    before(async () => {
+      ({app, client} = await setupApplication({
+        lb3app: {path: '../fixtures/app-with-model'},
+      }));
+    });
+
+    it('binds datasource to the context', async () => {
+      const expected = require('../../../fixtures/app-with-model').dataSources
+        .memory;
+      const dsBindings = app.findByTag('datasource');
+      const key = dsBindings[0].key;
+      const ds = await app.get(key);
+      expect(ds).to.eql(expected);
+    });
+  });
 });

packages/booter-lb3app/src/lb3app.booter.ts

@@ -5,6 +5,7 @@
 
 import {BootBindings, Booter} from '@loopback/boot';
 import {CoreBindings, inject} from '@loopback/core';
+import {AnyObject, DataSource} from '@loopback/repository';
 import {
   ExpressRequestHandler,
   OpenApiSpec,
@@ -62,6 +63,19 @@ export class Lb3AppBooter implements Booter {
       this.mountRoutesOnly(lb3App, spec);
     }
 
+    const dataSources = lb3App.dataSources;
+    if (dataSources) {
+      const visited: DataSource[] = [];
+      Object.values(dataSources).forEach(ds => {
+        if (visited.includes(ds)) return;
+        visited.push(ds);
+        this.app
+          .bind(`datasources.lb3-${ds.name}`)
+          .to(ds)
+          .tag('datasource');
+      });
+    }
+
     // TODO(bajtos) Listen for the following events to update the OpenAPI spec:
     // - modelRemoted
     // - modelDeleted
@@ -137,4 +151,5 @@ export interface Lb3AppBooterOptions {
 
 interface Lb3Application extends ExpressApplication {
   handler(name: 'rest'): ExpressRequestHandler;
+  dataSources?: AnyObject;
 }