Entity Events

Historia

Lanzamiento	Modificaciones
21	Added events: validateSave / saving / afterSave / validateDrop / dropping / afterDrop
20 R10	se ha añadido un evento touched

Entity events are functions that are automatically invoked by ORDA each time entities and entity attributes are manipulated (added, deleted, or modified). You can write very simple events, and then make them more sophisticated.

No se puede activar directamente la ejecución de la función de evento. Events are called automatically by ORDA based on user actions or operations performed through code on entities and their attributes.

Entrada de blog relacionada

ORDA – Handle an event-driven logic during data persistence actions

Nota de compatibilidad

ORDA entity events in the datastore are equivalent to triggers in the 4D database. However, actions triggered at the 4D database level using the 4D classic language commands or standard actions do not trigger ORDA events.

Generalidades

Nivel del evento

A event function is always defined in the Entity class.

It can be set at the entity level and/or the attribute level (it includes computed attributes). In the first case, it will be triggered for any attributes of the entity; on the other case, it will only be triggered for the targeted attribute.

For the same event, you can define different functions for different attributes.

You can also define the same event at both attribute and entity levels. The attribute event is called first and then the entity event.

Ejecución en configuraciones remotas

Normalmente, los eventos ORDA se ejecutan en el servidor.

In client/server configuration however, the touched() event function can be executed on the server or the client, depending on the use of local keyword. A specific implementation on the client side allows the triggering of the event on the client.

nota

ORDA constructor() functions are always executed on the client.

With other remote configurations (i.e. Qodly applications, REST API requests, or requests through Open datastore), the touched() event function is always executed server-side. It means that you have to make sure the server can "see" that an attribute has been touched to trigger the event (see below).

Tabla resumen

La siguiente tabla lista los eventos ORDA junto con sus reglas.

Evento	Nivel	Nombre de la función	(C/S) Ejecutado en	Can stop action by returning an error
Instanciación de entidades	Entity	constructor()	client	no
Atributo tocado	Atributo	event touched <attrName>()	Depende de la palabra clave local	no
	Entity	event touched()	Depende de la palabra clave local	no
Antes de guardar una entidad	Atributo	validateSave <attrName>()	server	sí
	Entity	validateSave()	server	sí
Al guardar una entidad	Atributo	saving <attrName>()	server	sí
	Entity	saving()	server	sí
Después de guardar una entidad	Entity	afterSave()	server	no
Before dropping an entity	Atributo	validateDrop <attrName>()	server	sí
	Entity	validateDrop()	server	sí
Al soltar una entidad	Atributo	dropping <attrName>()	server	sí
	Entity	dropping()	server	sí
After dropping an entity	Entity	afterDrop()	server	no

nota

The constructor() function is not actually an event function but is always called when a new entity is instantiated.

Parámetro event

Event functions accept a single event object as parameter. When the function is called, the parameter is filled with several properties:

Nombre de propiedad	Disponibilidad	Tipo	Descripción
"kind"	siempre	String	Event name: "touched", "validateSave", "saving", "afterSave", "validateDrop", "dropping", "afterDrop"
attributeName	Only for events implemented at attribute level ("validateSave", "saving", "validateDrop", "dropping")	String	Nombre del atributo (por ejemplo, "nombre")
dataClassName	siempre	String	Nombre de la Dataclass (ej. "Company")
"savedAttributes"	Sólo en afterSave()	Colección de cadenas	Names of attributes properly saved
"droppedAttributes"	Sólo en afterDrop()	Colección de cadenas	Names of attributes properly dropped
"saveStatus"	Sólo en afterSave()	String	"success" if the save was successful, "failed" otherwise
"dropStatus"	Sólo en afterDrop()	String	"success" if the drop was successful, "failed" otherwise

Objeto de error

Some event functions can return an error object to raise an error and stop the running action.

When an error occurs in an event, the other events are stopped at the first raised error and the action (save or drop) is also stopped. This error is sent before other potential errors like stamp has changed, entity locked, etc.

Propiedades del objeto error

Propiedad	Tipo	Descripción	Definido por el desarrollador
errCode	Integer	Igual al comando Last errors	Sí
message	Text	Igual al comando Last errors	Sí
extraDescription	Object	Información libre a definir	Sí
seriousError	Boolean	Used only with validate events (see below). True: creates a serious (unpredictable) error and triggers an exception. Adds the dk status serious validation error status False: creates only a silent (predictable) error. Añade el estado dk status validation failed.	Sí (por defecto es false)
componentSignature	Text	Always "DBEV"	No

• Serious errors are stacked in the errors collection property of the Result object returned by the save() or drop() functions.
• In case of an error triggered by a validate event, the seriousError property allows you to choose the level of the error to generate:
  • If true: a serious error is thrown and should be handled by the error processing code, such as a try catch. In the result object of the calling function, status gets dk status serious validation error and statusText gets "Serious Validation Error". The error is raised at the end of the event and reach the client requesting the save/drop action (REST client for example).
  • If false (default): a silent (predictable) error is generated. It does not trigger any exception and is not stacked in the errors returned by the Last errors command. In the result object of the calling function, status gets dk status validation failed and statusText gets "Mild Validation Error".
• In case of an error triggered by a saving/dropping event, when an error object is returned, the error is always raised as a serious error whatever the seriousError property value.

Event function description

Function event touched

Sintaxis

{local} Function event touched($event : Object)
{local} Function event touched <attributeName>($event : Object)
// code

This event is triggered each time a value is modified in the entity.

• If you defined the function at the entity level (first syntax), it is triggered for modifications on any attribute of the entity.
• If you defined the function at the attribute level (second syntax), it is triggered only for modifications on this attribute.

This event is triggered as soon as the 4D Server / 4D engine can detect a modification of attribute value which can be due to the following actions:

• en cliente/servidor con la palabra clave local o en 4D monousuario:
  • el usuario define un valor en un formulario 4D,
  • el código 4D realiza una asignación con el operador :=. El evento también se activa en caso de autoasignación ($entity.attribute:=$entity.attribute).
• in client/server without the local keyword: some 4D code that makes an assignment with the := operator is executed on the server.
• in client/server without the local keyword, in Qodly application and remote datastore: the entity is received on 4D Server while calling an ORDA function (on the entity or with the entity as parameter). It means that you might have to implement a refresh or preview function on the remote application that sends an ORDA request to the server and triggers the event.
• with the REST server: the value is received on the REST server with a REST request ($method=update)

The function receives an event object as parameter.

If this function throws an error, it will not stop the undergoing action.

nota

Este evento también se activa:

• cuando los atributos son asignados por el evento constructor(),
• when attributes are edited through the Data Explorer.

Ejemplo 1

You want to uppercase all text attributes of an entity when it is updated.

    //ProductsEntity class
Function event touched($event : Object)
	
	If (Value type(This[$event.attributeName])=Is text)
		This[$event.attributeName]:=Uppercase(This[$event.attributeName])
	End if 

Ejemplo 2

The "touched" event is useful when it is not possible to write indexed query code in Function query() for a computed attribute.

This is the case for example, when your query function has to compare the value of different attributes from the same entity with each other. You must use formulas in the returned ORDA query -- which triggers sequential queries.

To fully understand this case, let's examine the following two calculated attributes:

Function get onGoing() : Boolean
        return ((This.departureDate<=Current date) & (This.arrivalDate>=Current date))

Function get sameDay() : Boolean
        return (This.departureDate=This.arrivalDate)

Even though they are very similar, these functions cannot be associated with identical queries because they do not compare the same types of values. The first compares attributes to a given value, while the second compares attributes to each other.

• For the onGoing attribute, the query function is simple to write and uses indexed attributes:

Function query onGoing($event : Object) : Object
    var $operator : Text
    var $myQuery : Text
    var $onGoingValue : Boolean
    var $parameters : Collection
    $parameters:=New collection()

    $operator:=$event.operator
    Case of 
            : (($operator="=") | ($operator="==") | ($operator="==="))
                $onGoingValue:=Bool($event.value)
            : (($operator="!=") | ($operator="!=="))
                $onGoingValue:=Not(Bool($event.value))
            Else 
                return {query: ""; parameters: $parameters}
    End case 

    $myQuery:=($onGoingValue) ? "departureDate <= :1 AND arrivalDate >= :1" : "departureDate > :1 OR arrivalDate < :1"
        // the ORDA query string uses indexed attributes, it will be indexed
    $parameters.push(Current date)
    return {query: $myQuery; parameters: $parameters}

• For the sameDay attribute, the query function requires an ORDA query based on formulas and will be sequential:

Function query sameDay($event : Object) : Text
    var $operator : Text
    var $sameDayValue : Boolean

    $operator:=$event.operator
    Case of 
        : (($operator="=") | ($operator="==") | ($operator="==="))
            $sameDayValue:=Bool($event.value)
        : (($operator="!=") | ($operator="!=="))
            $sameDayValue:=Not(Bool($event.value))
        Else 
            return ""
        End case 

    return ($sameDayValue) ? "eval(This.departureDate = This.arrivalDate)" : "eval(This.departureDate != This.arrivalDate)"
        // the ORDA query string uses a formula, it will not be indexed

• Using a scalar sameDay attribute updated when other attributes are "touched" will save time:

    //BookingEntity class

Function event touched departureDate($event : Object) 

    This.sameDay:=(This.departureDate = This.arrivalDate) 
//
//
Function event touched arrivalDate($event : Object) 

    This.sameDay:=(This.departureDate = This.arrivalDate)

Ejemplo 3 (diagrama): cliente/servidor con la palabra clave local:

Ejemplo 4 (diagrama): cliente/servidor sin la palabra clave local

Ejemplo 5 (diagrama): Aplicación Qodly

Function event validateSave

Sintaxis

Function event validateSave($event : Object)
Function event validateSave <attributeName>($event : Object)
// code

This event is triggered each time an entity is about to be saved.

• if you defined the function at the entity level (first syntax), it is called for any attribute of the entity.
• if you defined the function at the attribute level (second syntax), it is called only for this attribute. This function is not executed if the attribute has not been touched in the entity.

The function receives an event object as parameter.

This event is triggered by the following functions:

• entity.save()
• dataClass.fromCollection()

This event is triggered before the entity is actually saved and lets you check data consistency so that you can stop the action if needed. For example, you can check in this event that "departure date" < "arrival date".

To stop the action, the code of the function must return an error object.

nota

It is not recommended to update the entity within this function (using This).

Ejemplo

In this example, it is not allowed to save a product with a margin lower than 50%. In case of an invalid price attribute, you return an error object and thus, stop the save action.

// ProductsEntity class
//
// validateSave event at attribute level
Function event validateSave margin($event : Object) : Object
	
var $result : Object
	
//The user can't create a product whose margin is < 50%
If (This.margin<50)
	$result:={errCode: 1; message: "The validation of this product failed"; \
	extraDescription: {info: "The margin of this product ("+String(This.margin)+") is lower than 50%"}; seriousError: False}
End if 
return $result

Function event saving

Sintaxis

Function event saving($event : Object)
Function event saving <attributeName>($event : Object)
// code

This event is triggered each time an entity is being saved.

• If you defined the function at the entity level (first syntax), it is called for any attribute of the entity. The function is executed even if no attribute has been touched in the entity (e.g. in case of sending data to an external app each time a save is done).
• If you defined the function at the attribute level (second syntax), it is called only for this attribute. The function is not executed if the attribute has not been touched in the entity.

The function receives an event object as parameter.

This event is triggered by the following functions:

• entity.save()
• dataClass.fromCollection()

This event is triggered while the entity is actually saved. If a validateSave() event function was defined, the saving() event function is called if no error was triggered by validateSave(). For example, you can use this event to create a document on a Google Drive account.

nota

The business logic should raise errors which can't be detected during the validateSave() events, e.g. a network error

During the save action, 4D engine errors can be raised (index, stamp has changed, not enough space on disk).

To stop the action, the code of the function must return an error object.

Ejemplo

When a file is saved on disk, catch errors related to disk space for example.

// ProductsEntity class
// saving event at attribute level
Function event saving userManualPath($event : Object) : Object
	
var $result : Object
var $userManualFile : 4D.File
var $fileCreated : Boolean
	
If (This.userManualPath#"")
	$userManualFile:=File(This.userManualPath)
				
	// The user manual document file is created on the disk
	// This may fail if no more space is available
	Try
		$fileCreated:=$userManualFile.create() 
	Catch
		// No more room on disk for example
		$result:={/
            errCode: 1; message: "Error during the save action for this product"; /
            extraDescription: {info: "There is no available space on disk to store the user manual"}/
        }
	End try
End if 
	
return $result

Function event afterSave

Sintaxis

Function event afterSave($event : Object)
// code

This event is triggered just after an entity is saved in the data file, when at least one attribute was modified. It is not executed if no attribute has been touched in the entity.

This event is useful after saving data to propagate the save action outside the application or to execute administration tasks. For example, it can be used to send a confirmation email after data have been saved. Or, in case of error while saving data, it can make a rollback to restore a consistent state of data.

The function receives an event object as parameter.

• To avoid infinite loops, calling a save() on the current entity (through This) in this function is not allowed. Se producirá un error.
• Throwing an error object is not supported by this function.

Ejemplo

If an error occurred in the above saving event, the attribute value is reset accordingly in the afterSave event:

// ProductsEntity class
Function event afterSave($event : Object)
	
If (($event.status.success=False) && ($event.status.errors=Null))  
    // $event.status.errors is filled if the error comes from the validateSave event
		
	// The userManualPath attribute has not been properly saved
	// Its value is reset
	If ($event.savedAttributes.indexOf("userManualPath")=-1)
		This.userManualPath:=""
		This.status:="KO"
	End if 
		
End if 

Function event validateDrop

Sintaxis

Function event validateDrop($event : Object)
Function event validateDrop <attributeName>($event : Object)
// code

This event is triggered each time an entity is about to be dropped.

• If you defined the function at the entity level (first syntax), it is called for any attribute of the entity.
• If you defined the function at the attribute level (second syntax), it is called only for this attribute.

The function receives an event object as parameter.

This event is triggered by the following features:

• entity.drop()
• entitySelection.drop()
• deletion control rules that can be defined at the database structure level.

This event is triggered before the entity is actually dropped, allowing you to check data consistency and if necessary, to stop the drop action.

To stop the action, the code of the function must return an error object.

Ejemplo

In this example, it is not allowed to drop a product that is not labelled "TO DELETE". In this case, you return an error object and thus, stop the drop action.

// ProductsEntity class

Function event validateDrop status($event : Object) : Object

var $result : Object

// Products must be marked as TO DELETE to be dropped
If (This.status#"TO DELETE")
    $result:={errCode: 1; message: "You can't drop this product"; \
    extraDescription: {info: "This product must be marked as To Delete"}; seriousError: False}
End if 

return $result

Function event dropping

Sintaxis

Function event dropping($event : Object)
Function event dropping <attributeName>($event : Object)
// code

This event is triggered each time an entity is being dropped.

• If you defined the function at the entity level (first syntax), it is called for any attribute of the entity.
• If you defined the function at the attribute level (second syntax), it is called only for this attribute.

The function receives an event object as parameter.

This event is triggered by the following features:

• entity.drop()
• entitySelection.drop()
• deletion control rules that can be defined at the database structure level.

This event is triggered while the entity is actually dropped. If a validateDrop() event function was defined, the dropping() event function is called if no error was triggered by validateDrop().

nota

The business logic should raise errors which cannot be detected during the validateDrop() events, e.g. a network error.

To stop the action, the code of the function must return an error object.

Ejemplo

Here is an example of dropping event at entity level:

// ProductsEntity class
Function event dropping($event : Object) : Object

var $result : Object
var $userManualFile : 4D.File

$userManualFile:=File(This.userManualPath)

    // When dropping a product, its user manual is also deleted on the disk
    // This action may fail
Try
    If ($userManualFile.exists)
        $userManualFile.delete()
    End if 
Catch
    // Dropping the user manual failed
    $result:={errCode: 1; message: "Drop failed"; extraDescription: {info: "The user manual can't be dropped"}}
End try

return $result

Function event afterDrop

Sintaxis

Function event afterDrop($event : Object)
// code

This event is triggered just after an entity is dropped.

This event is useful after dropping data to propagate the drop action outside the application or to execute administration tasks. For example, it can be used to send a cancellation email after data have been dropped. Or, in case of error while dropping data, it can log an information for the administrator to check data consistency.

The function receives an event object as parameter.

• To avoid infinite loops, calling a drop() on the current entity (through This) in this function is not allowed. Se producirá un error.
• Throwing an error object is not supported by this function.

nota

The dropped entity is referenced by This and still exists in memory.

Ejemplo

If the drop action failed, then the product must be checked manually:

Function event afterDrop($event : Object)

var $status : Object

If (($event.status.success=False) && ($event.status.errors=Null)) 
        //$event.status.errors is filled 
        //if the error comes from the validateDrop event
    This.status:="Check this product - Drop action failed"
    $status:=This.save()
End if