[CLI] Generate DataSource

[dhmlau]

Description / Feature proposal

CLI command to generate datasource. It generates either:

• datasource.ts, or;
• datasource.json with DataSource class that reads datasource.json

Sample for the first approach:

• https://github.com/strongloop/loopback-next/blob/master/packages/repository/examples/juggler-bridge/note-with-repo-class.ts#L22-L25

Sample for the latter approach:

• datasource.json: https://github.com/strongloop/loopback-next/blob/master/packages/example-todo/config/datasources.json
• datasource.ts: https://github.com/strongloop/loopback-next/blob/master/packages/example-todo/src/datasources/db.datasource.ts

User Experience

$lb datasource
? Enter the datasource name: testds
? Select the connector for testds: (selection of connectors) PostgreSQL (supported by StrongLoop)
? Connection String url to override other settings (eg: postgres://username:password@localhost/database): postgres://username:password@localhost/database
? host: localhost
? port: 5432
? user: username
? password: ****
? database: testdb
? Install loopback-connector-postgresql@^2.4 No

As a result, src/datasources/testds.datasource.ts will be generated.

Outstanding questions

• What should we be generating? just the datasource.ts? or similar to what we have in example-todo?
• For the list of connectors for selection, do we want to have the same list as in LB3?

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Acceptance Criteria

• Create lb4 datasource -- works like LB3 CLI with the following changes:
  • Each datasource config is stored in it's own .json file
  • An accompanying .ts file is created which injects the datasource config
• Tests as usual
• Not related but relevant: @loopback/boot will bind JSON config files to Context
  • Must provide a way to override from env ...

[dhmlau]

Things to consider:

1. CLI to generate the datasource
2. bootstrap any LB3 datasources.json and model definition.