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Application Services ​

Class cds.ApplicationService ​

Class cds.ApplicationService is the default service provider implementation, adding generic handlers as introduced in the Cookbook guides on Providing Services, Localized Data and Temporal Data.

For example, given a service definition like that, without an :

cds
service AdminService {
  entity Authors as projection on my.Authors;
  entity Books as projection on my.Books;
  entity Genre as projection on my.Genre;
}
service AdminService {
  entity Authors as projection on my.Authors;
  entity Books as projection on my.Books;
  entity Genre as projection on my.Genre;
}

Without any custom service implementation in place, cds.serve would create and instantiate instances of cds.ApplicationService by default like so:

js
// srv/admin-service.cds
let name = 'AdminService', options = {...}
let srv = new cds.ApplicationService (name, cds.model, options)
await srv.init()
// srv/admin-service.cds
let name = 'AdminService', options = {...}
let srv = new cds.ApplicationService (name, cds.model, options)
await srv.init()

If you add a custom implementation, this would comonly be derived from cds.ApplicationService:

js
// srv/admin-service.js
const cds = require('@sap/cds')
module.exports = class AdminService extends cds.ApplicationService {
  init() {
    // register your handlers ...
    return super.init()
  }
}
// srv/admin-service.js
const cds = require('@sap/cds')
module.exports = class AdminService extends cds.ApplicationService {
  init() {
    // register your handlers ...
    return super.init()
  }
}

Generic Handlers in srv.init() ​

Generic handlers are registered by via respective class methods documented below in cds.ApplicationService.prototype.init() like so:

tsx
class cds.ApplicationService extends cds.Service {
  init() {
    const generics = //... all static method with prefix 'handle_'
    for (let each of generics) this[each].call(this)
    return super.init()
  }
  static handle_authorization() {...}
  static handle_etags() {...}
  static handle_validations() {...}
  static handle_temporal_data() {...}
  static handle_localized_data() {...}
  static handle_managed_data() {...}
  static handle_paging() {...}
  static handle_fiori() {...}
  static handle_crud() {...}
}
class cds.ApplicationService extends cds.Service {
  init() {
    const generics = //... all static method with prefix 'handle_'
    for (let each of generics) this[each].call(this)
    return super.init()
  }
  static handle_authorization() {...}
  static handle_etags() {...}
  static handle_validations() {...}
  static handle_temporal_data() {...}
  static handle_localized_data() {...}
  static handle_managed_data() {...}
  static handle_paging() {...}
  static handle_fiori() {...}
  static handle_crud() {...}
}

The reason we used static methods was to (a) give you an easy way of overriding and adding new generic handlers / features, and (b) without getting into conflicts with instance methods of subclasses.

static handle_authorization() ​

This method is adding request handlers for initial authorization checks, as documented in the Authorization guide.

static handle_etags() ​

This method is adding request handlers for out-of-the-box concurrency control using ETags, as documented in the Providing Services guide.

static handle_validations() ​

This method is adding request handlers for input validation based in @assert annotations, and other, as documented in the Providing Services guide.

static handle_temporal_data() ​

This method is adding request handlers for handling temporal data, as documented in the Temporal Data guide.

static handle_localized_data() ​

This method is adding request handlers for handling localized data, as documented in the Localized Data guide.

static handle_managed_data() ​

This method is adding request handlers for handling managed data, as documented in the Providing Services guide.

static handle_paging() ​

This method is adding request handlers for paging & implicit sorting, as documented in the Providing Services guide.

static handle_fiori() ​

This method is adding request handlers for handling Fiori Drafts and other Fiori-specifics, as documented in the Serving Fiori guide.

static handle_crud() ​

This method is adding request handlers for all CRUD operations including deep CRUD, as documented in the Providing Services guide.

Overriding Generic Handlers ​

You can override some of these methods in subclasses, for example to skip certain generic features, or to add additional ones. For example like that:

js
class YourService extends cds.ApplicationService {
  static handle_validations() {
    // Note: this is an instance of YourService here:
    this.on('CREATE','*', req => {...})
    return super.handle_validations()
  }
}
class YourService extends cds.ApplicationService {
  static handle_validations() {
    // Note: this is an instance of YourService here:
    this.on('CREATE','*', req => {...})
    return super.handle_validations()
  }
}

Adding Generic Handlers ​

You can also add own sets of generic handlers to all instances of cds.ApplicationService, and subclasses thereof, by simply adding a new class method prefixed with handle_ like so:

js
const cds = require('@sap/cds')
cds.ApplicationService.handle_log_events = cds.service.impl (function(){
  this.on('*', req => console.log(req.event))
})
const cds = require('@sap/cds')
cds.ApplicationService.handle_log_events = cds.service.impl (function(){
  this.on('*', req => console.log(req.event))
})