loopbackjs: Attach a model to different datasources
As @superkhau pointed above, each LoopBack Model can be attached to a single data-source only.
You can create (subclass) a new model for each datasource you want to use. Then you can either expose these per-datasource models via unique REST URLs, or you can implement a wrapper model that will dispatch methods to the correct datasource-specific model.
In my example, I'll show how to expose per-datasource models for a Car
model that is attached to db
and anotherdb
. The Car
model is defined in the usual way via common/models/car.json
and common/models/car.js
.
Now you need to define per-datasource models:
// common/models/car-db.js
{
"name": "Car-db",
"base": "Car",
"http": {
"path": "/cars:db"
}
}
// common/models/car-anotherdb.js
{
"name": "Car-anotherdb",
"base": "Car",
"http": {
"path": "/cars:anotherdb"
}
}
// server/model-config.json
{
"Car": {
"dataSource": "default"
},
"Car-db": {
"dataSource": "db"
},
"Car-anotherdb": {
"dataSource": "anotherdb"
}
}
Now you have the following URLs available:
GET /api/Cars:db
GET /api/Cars:anotherdb
GET /api/Cars
The solution outlined above has two limitations: you have to define a new model for each datasource and the datasource cannot be selected using a query parameter.
To fix that, you need a different approach. I'll again assume there is a Car
model already defined.
Now you need to create a "dispatcher".
// common/models/car-dispatcher.json
{
"name": "CarDispatcher",
"base": "Model", //< important!
"http": {
"path": "/cars"
}
}
// common/models/car-dispatcher.js
var loopback = require('loopback').PersistedModel;
module.exports = function(CarDispatcher) {
Car.find = function(ds, filter, cb) {
var model = this.findModelForDataSource(ds);
model.find(filter, cb);
};
// a modified copy of remoting metadata from loopback/lib/persisted-model.js
Car.remoteMethod('find', {
isStatic: true,
description: 'Find all instances of the model matched by filter from the data source',
accessType: 'READ',
accepts: [
{arg: 'ds', type: 'string', description: 'Name of the datasource to use' },
{arg: 'filter', type: 'object', description: 'Filter defining fields, where, orderBy, offset, and limit'}
],
returns: {arg: 'data', type: [typeName], root: true},
http: {verb: 'get', path: '/'}
});
// TODO: repeat the above for all methods you want to expose this way
Car.findModelForDataSource = function(ds) {
var app = this.app;
var ds = ds && app.dataSources[ds] || app.dataSources.default;
var modelName = this.modelName + '-' + ds;
var model = loopback.findModel(modelName);
if (!model) {
model = loopback.createModel(
modelName,
{},
{ base: this.modelName });
}
return model;
};
};
The final bit is to remove Car
and use CarDispatcher
in the model config:
// server/model-config.json
{
"CarDispatcher": {
dataSource: null,
public: true
}
}