Page Contents


Datasources are LoopBack’s way of connecting to various sources of data, such as databases, APIs, message queues and more. A DataSource in LoopBack 4 is a named configuration for a Connector instance that represents data in an external system. The Connector is used by legacy-juggler-bridge to power LoopBack 4 Repositories for Data operations.

In LoopBack 4, datasources can be represented as strongly-typed objects and freely made available for injection throughout the application. Typically, in LoopBack 4, datasources are used in conjunction with Repositories to provide access to data.

For more information about datasources in LoopBack, see DataSources.

Since our Todo API will need to persist instances of Todo items, we’ll need to create a datasource definition to make this possible.

Building a Datasource

From inside the project folder, we’ll run the lb4 datasource command to create a DataSource. For the purposes of this tutorial, we’ll be using the memory connector provided with the Juggler.

lb4 datasource
? Datasource name: db
? Select the connector for db: In-memory db (supported by StrongLoop)
? window.localStorage key to use for persistence (browser only):
? Full path to file for persistence (server only): ./data/db.json

  create src/datasources/db.datasource.ts
  update src/datasources/index.ts

Datasource Db was created in src/datasources/

To view the completed files, see the Todo example.

Create a data folder in the applications root and add a new file called db.json containing an example database.


  "ids": {
    "Todo": 5
  "models": {
    "Todo": {
      "1": "{\"title\":\"Take over the galaxy\",\"desc\":\"MWAHAHAHAHAHAHAHAHAHAHAHAHAMWAHAHAHAHAHAHAHAHAHAHAHAHA\",\"id\":1}",
      "2": "{\"title\":\"destroy alderaan\",\"desc\":\"Make sure there are no survivors left!\",\"id\":2}",
      "3": "{\"title\":\"play space invaders\",\"desc\":\"Become the very best!\",\"id\":3}",
      "4": "{\"title\":\"crush rebel scum\",\"desc\":\"Every.Last.One.\",\"id\":4}"

Once you’re ready, we’ll move onto adding a repository for the datasource.

Previous step: Add your Todo model

Next step: Add a repository