Attaching models to data sources

Overview

A data source enables a model to access and modify data in backend system such as a relational database.  Data sources encapsulate business logic to exchange data between models and various back-end systems such as relational databases, REST APIs, SOAP web services, storage services, and so on. Data sources generally provide create, retrieve, update, and delete (CRUD) functions. 

Models access data sources through connectors that are extensible and customizable. In general, application code does not use a connector directly. Rather, the DataSource class provides an API to configure the underlying connector.

The built-in memory connector is suitable for development. To use a different data source:

1. Use the data source generator  to create the new data source and add it to the application’s datasources.json.
2. Edit datasources.json to add the appropriate credentials for the data source.
3. Create a model to connect to the data source or modify an existing model definition to use the connector.

Add a data source

To add a new data source, use the data source generator:

$ slc loopback:datasource

Or, with API Connect:

$ apic create --type datasource

You can also add and modify data sources using the API Designer tool.

The tool will prompt you for the name of the new data source and the connector to use; for example, MySQL, Oracle, REST, and so on. The tool will then add an entry such as the following to datasources.json:

  ...
  "corp1": {
    "name": "corp1",
    "connector": "mysql"
  }
  ...

This example creates a MySQL data source called “corp1”. The identifier determines the name by which you refer to the data source and can be any string.

Next, the generator will prompt you to type the datasource settings, such as host, port, user, password and database name, as well as to install the database connector.

? Enter the datasource name: corp1
? Select the connector for corp1: MySQL (supported by StrongLoop)
? Connection String url to override other settings (eg: mysql://user:pass@host/db):
? host: your-mysql-server.foo.com
? port: 3306
? user: demo
? password: ****
? database: demo
? Install loopback-connector-mysql@^1.4 Yes

Install the database connector when it prompts you or if you wish to install separately you can do so by npm install loopback-connector-<connector_name> --save. If you do not enter the database credentials when prompted, then you must add them manually to server/datasources.json as shown below.

Add data source credentials

Edit server/datasources.json to add the necessary authentication credentials for the data source; typically hostname, username, password, and database name.

For example:

"corp1": {
    "name": "corp1",
    "connector": "mysql",
    "host": "your-mysql-server.foo.com",
    "user": "db-username",
    "password": "db-password",
    "database": "your-db-name"
  }

Make the model use the data source

When you create a new model with the model generator, you can specify the data source you want it to use from among those you’ve added to the application using the Data source generator and the default db data source (that uses the memory connector).

To create a model, run slc loopback:model or apic create --type model.

? Enter the model name: myModel
? Select the data-source to attach myModel to:
   db (memory)
 ❯ corp1 (mysql)
   (no data-source) 

To change the data source a model uses after you’ve created the model, edit the application’s server/model-config.json and set the dataSource property for the model. For example, to make myModel use the corp1 data source:

"myModel": {
    "dataSource": "corp1",
    "public": true
  }

By default, the model generator creates models to use the db data source.