Version: Next

Data Model Classes

ORDA allows you to create high-level class functions above the data model. This allows you to write business-oriented code and "publish" it just like an API. Datastore, dataclasses, entity selections, and entities are all available as class objects that can contain functions.

For example, you could create a getNextWithHigherSalary() function in the EmployeeEntity class to return employees with a salary higher than the selected one. It would be as simple as calling:

$nextHigh:=ds.Employee.get(1).getNextWithHigherSalary()

Developers can not only use these functions in local datastores, but also in client/server and remote architectures:

 //$cityManager is the reference of a remote datastore
Form.comp.city:=$cityManager.City.getCityName(Form.comp.zipcode)

Thanks to this feature, the entire business logic of your 4D application can be stored as a independent layer so that it can be easily maintained and reused with a high level of security:

You can "hide" the overall complexity of the underlying physical structure and only expose understandable and ready-to-use functions.
If the physical structure evolves, you can simply adapt function code and client applications will continue to call them transparently.
By default, all of your data model class functions (including computed attribute functions) and alias attributes are not exposed to remote applications and cannot be called from REST requests. You must explicitly declare each public function and alias with the exposed keyword.

In addition, 4D automatically pre-creates the classes for each available data model object.

Architecture

ORDA provides generic classes exposed through the 4D class store, as well as user classes (extending generic classes) exposed in the cs class store:

All ORDA data model classes are exposed as properties of the cs class store. The following ORDA classes are available:

Class	Example name	Instantiated by
cs.DataStore	cs.DataStore	`ds` command
cs.DataClassName	cs.Employee	`dataStore.DataClassName`, `dataStore["DataClassName"]`
cs.DataClassNameEntity	cs.EmployeeEntity	`dataClass.get()`, `dataClass.new()`, `entitySelection.first()`, `entitySelection.last()`, `entity.previous()`, `entity.next()`, `entity.first()`, `entity.last()`, `entity.clone()`
cs.DataClassNameSelection	cs.EmployeeSelection	`dataClass.query()`, `entitySelection.query()`, `dataClass.all()`, `dataClass.fromCollection()`, `dataClass.newSelection()`, `entitySelection.drop()`, `entity.getSelection()`, `entitySelection.and()`, `entitySelection.minus()`, `entitySelection.or()`, `entitySelection.orderBy()`, `entitySelection.orderByFormula()`, `entitySelection.slice()`, `Create entity selection`

ORDA user classes are stored as regular class files (.4dm) in the Classes subfolder of the project (see below).

Also, object instances from ORDA data model user classes benefit from their parent's properties and functions:

a Datastore class object can call functions from the ORDA Datastore generic class.
a Dataclass class object can call functions from the ORDA Dataclass generic class.
an Entity selection class object can call functions from the ORDA Entity selection generic class.
an Entity class object can call functions from the ORDA Entity generic class.

Class Description

History

Release	Changes
19 R4	Alias attributes in the Entity Class
19 R3	Computed attributes in the Entity Class
18 R5	Data model class functions are not exposed to REST by default. New `exposed` and `local` keywords.

DataStore Class

A 4D database exposes its own DataStore class in the cs class store.

Extends: 4D.DataStoreImplementation
Class name: cs.DataStore

You can create functions in the DataStore class that will be available through the ds object.

Example

// cs.DataStore class

Class extends DataStoreImplementation

Function getDesc
  $0:="Database exposing employees and their companies"

This function can then be called:

$desc:=ds.getDesc() //"Database exposing..."

DataClass Class

Each table exposed with ORDA offers a DataClass class in the cs class store.

Extends: 4D.DataClass
Class name: cs.DataClassName (where DataClassName is the table name)
Example name: cs.Employee

Example

// cs.Company class


Class extends DataClass

// Returns companies whose revenue is over the average
// Returns an entity selection related to the Company DataClass

Function GetBestOnes()
	$sel:=This.query("revenues >= :1";This.all().average("revenues"));
	$0:=$sel

Then you can get an entity selection of the "best" companies by executing:

	var $best : cs.CompanySelection
	$best:=ds.Company.GetBestOnes()

info

Computed attributes are defined in the Entity Class.

Example with a remote datastore

The following City catalog is exposed in a remote datastore (partial view):

The City Class provides an API:

// cs.City class

Class extends DataClass

Function getCityName()
	var $1; $zipcode : Integer
	var $zip : 4D.Entity
	var $0 : Text

	$zipcode:=$1
	$zip:=ds.ZipCode.get($zipcode)
	$0:=""

	If ($zip#Null)
		$0:=$zip.city.name
	End if

The client application opens a session on the remote datastore:

$cityManager:=Open datastore(New object("hostname";"127.0.0.1:8111");"CityManager")

Then a client application can use the API to get the city matching a zip code (for example) from a form:

Form.comp.city:=$cityManager.City.getCityName(Form.comp.zipcode)

EntitySelection Class

Each table exposed with ORDA offers an EntitySelection class in the cs class store.

Extends: 4D.EntitySelection
Class name: DataClassNameSelection (where DataClassName is the table name)
Example name: cs.EmployeeSelection

Example

// cs.EmployeeSelection class

Class extends EntitySelection

//Extract the employees with a salary greater than the average from this entity selection

Function withSalaryGreaterThanAverage() : cs.EmployeeSelection
	return This.query("salary > :1";This.average("salary")).orderBy("salary")

Then you can get employees with a salary greater than the average in any entity selection by executing:

$moreThanAvg:=ds.Company.all().employees.withSalaryGreaterThanAverage()

info

Restricted entity selection filters are defined in the Dataclass Class.

Entity Class

Each table exposed with ORDA offers an Entity class in the cs class store.

Extends: 4D.Entity
Class name: DataClassNameEntity (where DataClassName is the table name)
Example name: cs.CityEntity

Computed attributes

Entity classes allow you to define computed attributes using specific keywords:

Function get attributeName
Function set attributeName
Function query attributeName
Function orderBy attributeName

For information, please refer to the Computed attributes section.

Alias attributes

Entity classes allow you to define alias attributes, usually over related attributes, using the Alias keyword:

Alias attributeName targetPath

For information, please refer to the Alias attributes section.

Example

// cs.CityEntity class

Class extends Entity

Function getPopulation() : Integer
    return This.zips.sum("population")


Function isBigCity(): Boolean
// The getPopulation() function is usable inside the class
	return This.getPopulation()>50000

Then you can call this code:

var $cityManager; $city : Object

$cityManager:=Open datastore(New object("hostname";"127.0.0.1:8111");"CityManager")
$city:=$cityManager.City.getCity("Caguas")

If ($city.isBigCity())
	ALERT($city.name + " is a big city")
End if

Specific rules

When creating or editing data model classes, you must pay attention to the following rules:

Since they are used to define automatic DataClass class names in the cs class store, 4D tables must be named in order to avoid any conflict in the cs namespace. In particular:
- Do not give the same name to a 4D table and to a user class name. If such a case occurs, the constructor of the user class becomes unusable (a warning is returned by the compiler).
- Do not use a reserved name for a 4D table (e.g., "DataClass").
When defining a class, make sure the Class extends statement exactly matches the parent class name (remember that they're case sensitive). For example, Class extends EntitySelection for an entity selection class.
You cannot instantiate a data model class object with the new() keyword (an error is returned). You must use a regular method as listed in the Instantiated by column of the ORDA class table.
You cannot override a native ORDA class function from the 4D class store with a data model user class function.

Preemptive execution

When compiled, data model class functions are executed:

in preemptive or cooperative processes (depending on the calling process) in single-user applications,
in preemptive processes in client/server applications (except if the local keyword is used, in which case it depends on the calling process like in single-user).

If your project is designed to run in client/server, make sure your data model class function code is thread-safe. If thread-unsafe code is called, an error will be thrown at runtime (no error will be thrown at compilation time since cooperative execution is supported in single-user applications).

Computed attributes

Overview

A computed attribute is a dataclass attribute with a data type that masks a calculation. Standard 4D classes implement the concept of computed properties with get (getter) and set (setter) accessor functions. ORDA dataclass attributes benefit from this feature and extend it with two additional functions: query and orderBy.

At the very minimum, a computed attribute requires a get function that describes how its value will be calculated. When a getter function is supplied for an attribute, 4D does not create the underlying storage space in the datastore but instead substitutes the function's code each time the attribute is accessed. If the attribute is not accessed, the code never executes.

A computed attribute can also implement a set function, which executes whenever a value is assigned to the attribute. The setter function describes what to do with the assigned value, usually redirecting it to one or more storage attributes or in some cases other entities.

Just like storage attributes, computed attributes may be included in queries. By default, when a computed attribute is used in a ORDA query, the attribute is calculated once per entity examined. In some cases this is sufficient. However for better performance, especially in client/server, computed attributes can implement a query function that relies on actual dataclass attributes and benefits from their indexes.

Similarly, computed attributes can be included in sorts. When a computed attribute is used in a ORDA sort, the attribute is calculated once per entity examined. Just like in queries, computed attributes can implement an orderBy function that substitutes other attributes during the sort, thus increasing performance.

How to define computed attributes

You create a computed attribute by defining a get accessor in the entity class of the dataclass. The computed attribute will be automatically available in the dataclass attributes and in the entity attributes.

Other computed attribute functions (set, query, and orderBy) can also be defined in the entity class. They are optional.

Within computed attribute functions, This designates the entity. Computed attributes can be used and handled as any dataclass attribute, i.e. they will be processed by entity class or entity selection class functions.

ORDA computed attributes are not exposed by default. You expose a computed attribute by adding the exposed keyword to the get function definition.

get and set functions can have the local property to optimize client/server processing.

`Function get <attributeName>`

Syntax

{local} {exposed} Function get <attributeName>({$event : Object}) -> $result : type
// code

The getter function is mandatory to declare the attributeName computed attribute. Whenever the attributeName is accessed, 4D evaluates the Function get code and returns the $result value.

A computed attribute can use the value of other computed attribute(s). Recursive calls generate errors.

The getter function defines the data type of the computed attribute thanks to the $result parameter. The following resulting types are allowed:

Scalar (text, boolean, date, time, number)
Object
Image
BLOB
Entity (i.e. cs.EmployeeEntity)
Entity selection (i.e. cs.EmployeeSelection)

The $event parameter contains the following properties:

Property	Type	Description
attributeName	Text	Computed attribute name
dataClassName	Text	Dataclass name
kind	Text	"get"
result	Variant	Optional. Add this property with Null value if you want a scalar attribute to return Null

Examples

fullName computed attribute:

Function get fullName($event : Object)-> $fullName : Text

  Case of 	
	: (This.firstName=Null) & (This.lastName=Null)
		$event.result:=Null //use result to return Null
	: (This.firstName=Null)
		$fullName:=This.lastName
	: (This.lastName=Null)
		$fullName:=This.firstName
	Else
		$fullName:=This.firstName+" "+This.lastName
	End case

A computed attribute can be based upon an entity related attribute:

Function get bigBoss($event : Object)-> $result: cs.EmployeeEntity
	$result:=This.manager.manager

A computed attribute can be based upon an entity selection related attribute:

Function get coWorkers($event : Object)-> $result: cs.EmployeeSelection
    If (This.manager.manager=Null)
        $result:=ds.Employee.newSelection()
    Else
        $result:=This.manager.directReports.minus(this)
    End if

`Function set <attributeName>`

Syntax

{local} Function set <attributeName>($value : type {; $event : Object})
// code

The setter function executes whenever a value is assigned to the attribute. This function usually processes the input value(s) and the result is dispatched between one or more other attributes.

The $value parameter receives the value assigned to the attribute.

The $event parameter contains the following properties:

Property	Type	Description
attributeName	Text	Computed attribute name
dataClassName	Text	Dataclass name
kind	Text	"set"
value	Variant	Value to be handled by the computed attribute

Example

Function set fullName($value : Text; $event : Object)
	var $p : Integer
    $p:=Position(" "; $value) 		
	This.firstname:=Substring($value; 1; $p-1)  // "" if $p<0
	This.lastname:=Substring($value; $p+1)

`Function query <attributeName>`

Syntax

Function query <attributeName>($event : Object)
Function query <attributeName>($event : Object) -> $result : Text
Function query <attributeName>($event : Object) -> $result : Object
// code

This function supports three syntaxes:

With the first syntax, you handle the whole query through the $event.result object property.
With the second and third syntaxes, the function returns a value in $result:
- If $result is a Text, it must be a valid query string
- If $result is an Object, it must contain two properties:
Property Type Description
$result.query Text Valid query string with placeholders (:1, :2, etc.)
$result.parameters Collection values for placeholders

Property	Type	Description
$result.query	Text	Valid query string with placeholders (:1, :2, etc.)
$result.parameters	Collection	values for placeholders

The query function executes whenever a query using the computed attribute is launched. It is useful to customize and optimize queries by relying on indexed attributes. When the query function is not implemented for a computed attribute, the search is always sequential (based upon the evaluation of all values using the get <AttributeName> function).

The following features are not supported:

calling a query function on computed attributes of type Entity or Entity selection,

using the order by keyword in the resulting query string.

The $event parameter contains the following properties:

Property	Type	Description
attributeName	Text	Computed attribute name
dataClassName	Text	Dataclass name
kind	Text	"query"
value	Variant	Value to be handled by the computed attribute
operator	Text	Query operator (see also the `query` class function). Possible values: == (equal to, @ is wildcard) === (equal to, @ is not wildcard) != (not equal to, @ is wildcard) !== (not equal to, @ is not wildcard) < (less than) <= (less than or equal to) > (greater than) >= (greater than or equal to) IN (included in) % (contains keyword)
result	Variant	Value to be handled by the computed attribute. Pass `Null` in this property if you want to let 4D execute the default query (always sequential for computed attributes).

If the function returns a value in $result and another value is assigned to the $event.result property, the priority is given to $event.result.

Examples

Query on the fullName computed attribute.

Function query fullName($event : Object)->$result : Object

	var $fullname; $firstname; $lastname; $query : Text
	var $operator : Text
	var $p : Integer
	var $parameters : Collection

	$operator:=$event.operator
	$fullname:=$event.value

	$p:=Position(" "; $fullname)
	If ($p>0)
		$firstname:=Substring($fullname; 1; $p-1)+"@"
		$lastname:=Substring($fullname; $p+1)+"@"
		$parameters:=New collection($firstname; $lastname) // two items collection
	Else
		$fullname:=$fullname+"@"
		$parameters:=New collection($fullname) // single item collection
	End if

	Case of
	: ($operator="==") | ($operator="===")
		If ($p>0)
			$query:="(firstName = :1 and lastName = :2) or (firstName = :2 and lastName = :1)"
		Else
			$query:="firstName = :1 or lastName = :1"
		End if
	: ($operator="!=")
		If ($p>0)
			$query:="firstName != :1 and lastName != :2 and firstName != :2 and lastName != :1"
		Else
			$query:="firstName != :1 and lastName != :1"
		End if
	End case

	$result:=New object("query"; $query; "parameters"; $parameters)

Keep in mind that using placeholders in queries based upon user text input is recommended for security reasons (see query() description).

Calling code, for example:

$emps:=ds.Employee.query("fullName = :1"; "Flora Pionsin")

This function handles queries on the age computed attribute and returns an object with parameters:

Function query age($event : Object)->$result : Object

	var $operator : Text
	var $age : Integer
	var $_ages : Collection

	$operator:=$event.operator

	$age:=Num($event.value)  // integer
	$d1:=Add to date(Current date; -$age-1; 0; 0)
	$d2:=Add to date($d1; 1; 0; 0)
	$parameters:=New collection($d1; $d2)

	Case of

		: ($operator="==")
			$query:="birthday > :1 and birthday <= :2"  // after d1 and before or egal d2

		: ($operator="===")

			$query:="birthday = :2"  // d2 = second calculated date (= birthday date)

		: ($operator=">=")
			$query:="birthday <= :2"

			//... other operators			


	End case


	If (Undefined($event.result))
		$result:=New object
		$result.query:=$query
		$result.parameters:=$parameters
	End if

Calling code, for example:

// people aged between 20 and 21 years (-1 day)
$twenty:=people.query("age = 20")  // calls the "==" case

// people aged 20 years today
$twentyToday:=people.query("age === 20") // equivalent to people.query("age is 20")

`Function orderBy <attributeName>`

Syntax

Function orderBy <attributeName>($event : Object)
Function orderBy <attributeName>($event : Object)-> $result : Text

// code

The orderBy function executes whenever the computed attribute needs to be ordered. It allows sorting the computed attribute. For example, you can sort fullName on first names then last names, or conversely. When the orderBy function is not implemented for a computed attribute, the sort is always sequential (based upon the evaluation of all values using the get <AttributeName> function).

Calling an orderBy function on computed attributes of type Entity class or Entity selection class is not supported.

The $event parameter contains the following properties:

Property	Type	Description
attributeName	Text	Computed attribute name
dataClassName	Text	Dataclass name
kind	Text	"orderBy"
value	Variant	Value to be handled by the computed attribute
operator	Text	"desc" or "asc" (default)
descending	Boolean	`true` for descending order, `false` for ascending order
result	Variant	Value to be handled by the computed attribute. Pass `Null` if you want to let 4D execute the default sort.

You can use either the operator or the descending property. It is essentially a matter of programming style (see examples).

You can return the orderBy string either in the $event.result object property or in the $result function result. If the function returns a value in $result and another value is assigned to the $event.result property, the priority is given to $event.result.

Example

You can write conditional code:

Function orderBy fullName($event : Object)-> $result : Text
    If ($event.descending=True)
        $result:="firstName desc, lastName desc"
    Else
        $result:="firstName, lastName"
    End if

You can also write compact code:

Function orderBy fullName($event : Object)-> $result : Text
	$result:="firstName "+$event.operator+", "lastName "+$event.operator

Conditional code is necessary in some cases:

Function orderBy age($event : Object)-> $result : Text

    If ($event.descending=True)
        $result:="birthday asc"
    Else
        $result:="birthday desc"
    End if

Alias attributes

Overview

An alias attribute is built above another attribute of the data model, named target attribute. The target attribute can belong to a related dataclass (available through any number of relation levels) or to the same dataclass. An alias attribute stores no data, but the path to its target attribute. You can define as many alias attributes as you want in a dataclass.

Alias attributes are particularly useful to handle N to N relations. They bring more readability and simplicity in the code and in queries by allowing to rely on business concepts instead of implementation details.

How to define alias attributes

You create an alias attribute in a dataclass by using the Alias keyword in the entity class of the dataclass.

`Alias <attributeName> <targetPath>`

Syntax

{exposed} Alias <attributeName> <targetPath>

attributeName must comply with standard rules for property names.

targetPath is an attribute path containing one or more levels, such as "employee.company.name". If the target attribute belongs to the same dataclass, targetPath is the attribute name.

An alias can be used as a part of a path of another alias.

A computed attribute can be used in an alias path, but only as the last level of the path, otherwise, an error is returned. For example, if "fullName" is a computed attribute, an alias with path "employee.fullName" is valid.

ORDA alias attributes are not exposed by default. You must add the exposed keyword before the Alias keyword if you want the alias to be available to remote requests.

Using alias attributes

Alias attributes are read-only (except when based upon a scalar attribute of the same dataclass, see the last example below). They can be used instead of their target attribute path in class functions such as:

Function
`dataClass.query()`, `entitySelection.query()`
`entity.toObject()`
`entitySelection.toCollection()`
`entitySelection.extract()`
`entitySelection.orderBy()`
`entitySelection.orderByFormula()`
`entitySelection.average()`
`entitySelection.count()`
`entitySelection.distinct()`
`entitySelection.sum()`
`entitySelection.min()`
`entitySelection.max()`
`entity.diff()`
`entity.touchedAttributes()`

Keep in mind that alias attributes are calculated on the server. In remote configurations, updating alias attributes in entities requires that entities are reloaded from the server.

Alias properties

Alias attribute kind is "alias".

An alias attribute inherits its data type property from the target attribute:

if the target attribute kind is "storage", the alias data type is of the same type,
if the target attribute kind is "relatedEntity" or "relatedEntities", the alias data type is of the 4D.Entity or 4D.EntitySelection type ("classnameEntity" or "classnameSelection").

Alias attributes based upon relations have a specific path property, containing the path of their target attributes. Alias attributes based upon attributes of the same dataclass have the same properties as their target attributes (and no path property).

Examples

Considering the following model:

In the Teacher dataclass, an alias attribute returns all students of a teacher:

// cs.TeacherEntity class

Class extends Entity

Alias students courses.student //relatedEntities

In the Student dataclass, an alias attribute returns all teachers of a student:

// cs.StudentEntity class

Class extends Entity

Alias teachers courses.teacher //relatedEntities

In the Course dataclass:

an alias attribute returns another label for the "name" attribute
an alias attribute returns the teacher name
an alias attribute returns the student name

// cs.CourseEntity class

Class extends Entity

Exposed Alias courseName name //scalar
Exposed Alias teacherName teacher.name //scalar value
Exposed Alias studentName student.name //scalar value

You can then execute the following queries:

// Find course named "Archaeology"
ds.Course.query("courseName = :1";"Archaeology")

// Find courses given by the professor Smith
ds.Course.query("teacherName = :1";"Smith")

// Find courses where Student "Martin" assists
ds.Course.query("studentName = :1";"Martin")

// Find students who have M. Smith as teacher
ds.Student.query("teachers.name = :1";"Smith")

// Find teachers who have M. Martin as Student
ds.Teacher.query("students.name = :1";"Martin")
// Note that this very simple query string processes a complex
// query including a double join, as you can see in the queryPlan:   
// "Join on Table : Course  :  Teacher.ID = Course.teacherID,    
//  subquery:[ Join on Table : Student  :  Course.studentID = Student.ID,
//  subquery:[ Student.name === Martin]]"

You can also edit the value of the courseName alias:

// Rename a course using its alias attribute
$arch:=ds.Course.query("courseName = :1";"Archaeology")
$arch.courseName:="Archaeology II"
$arch.save() //courseName and name are "Archaeology II"

Exposed vs non-exposed functions

For security reasons, all of your data model class functions and alias attributes are not exposed (i.e., private) by default to remote requests.

Remote requests include:

Requests sent by remote 4D applications connected through Open datastore
REST requests

Regular 4D client/server requests are not impacted. Data model class functions are always available in this architecture.

A function that is not exposed is not available on remote applications and cannot be called on any object instance from a REST request. If a remote application tries to access a non-exposed function, the "-10729 - Unknown member method" error is returned.

To allow a data model class function to be called by a remote request, you must explicitly declare it using the exposed keyword. The formal syntax is:

// declare an exposed function
exposed Function <functionName>

The exposed keyword can only be used with Data model class functions. If used with a regular user class function, it is ignored and an error is returned by the compiler.

Example

You want an exposed function to use a private function in a dataclass class:

Class extends DataClass

//Public function
exposed Function registerNewStudent($student : Object) -> $status : Object

var $entity : cs.StudentsEntity

$entity:=ds.Students.new()
$entity.fromObject($student)
$entity.school:=This.query("name=:1"; $student.schoolName).first()
$entity.serialNumber:=This.computeSerialNumber()
$status:=$entity.save()

//Not exposed (private) function
Function computeIDNumber()-> $id : Integer
//compute a new ID number
$id:=...

When the code is called:

var $remoteDS; $student; $status : Object
var $id : Integer

$remoteDS:=Open datastore(New object("hostname"; "127.0.0.1:8044"); "students")
$student:=New object("firstname"; "Mary"; "lastname"; "Smith"; "schoolName"; "Math school")

$status:=$remoteDS.Schools.registerNewStudent($student) // OK
$id:=$remoteDS.Schools.computeIDNumber() // Error "Unknown member method"

onHttpGet keyword

Use the onHttpGet keyword to declare functions that can be called through HTTP requests using the GET verb. Such functions can return any web contents, for example using the 4D.OutgoingMessage class.

The onHttpGet keyword is available with:

ORDA Data model class functions
Singletons class functions

The formal syntax is:

// declare an onHttpGet function
exposed onHttpGet Function <functionName>(params) : result

info

The exposed keyword must also be added in this case, otherwise an error will be generated.

caution

As this type of call is an easy offered action, the developer must ensure no sensitive action is done in such functions.

params

A function with onHttpGet keyword accepts parameters.

In the HTTP GET request, parameters must be passed directly in the URL and declared using the $params keyword (they must be enclosed in a collection).

IP:port/rest/<dataclass>/functionName?$params='[<params>]'

See the Parameters section in the REST server documentation.

result

A function with onHttpGet keyword can return any value of a supported type (same as for REST parameters).

info

You can return a value of the 4D.OutgoingMessage class type to benefit from properties and functions to set the header, the body, and the status of the answer.

Example

You have defined the following function:

Class extends DataClass

exposed onHTTPGet Function getThumbnail($name : Text; $width : Integer; $height : Integer) : 4D.OutgoingMessage
	
	var $file := File("/RESOURCES/Images/"+$name+".jpg")
	var $image; $thumbnail : Picture
	var $response := 4D.OutgoingMessage.new()
	
	READ PICTURE FILE($file.platformPath; $image)
	CREATE THUMBNAIL($image; $thumbnail; $width; $height; Scaled to fit)
	$response.setBody($thumbnail)	
	$response.setHeader("Content-Type"; "image/jpeg")
	return $response

It can be called by the following HTTP GET request:

IP:port/rest/Products/getThumbnail?$params='["Yellow Pack",200,200]'

Local functions

By default in client/server architecture, ORDA data model functions are executed on the server. It usually provides the best performance since only the function request and the result are sent over the network.

However, it could happen that a function is fully executable on the client side (e.g., when it processes data that's already in the local cache). In this case, you can save requests to the server and thus, enhance the application performance by inserting the local keyword. The formal syntax is:

// declare a function to execute locally in client/server
local Function <functionName>

With this keyword, the function will always be executed on the client side.

The local keyword can only be used with data model class functions. If used with a regular user class function, it is ignored and an error is returned by the compiler.

Note that the function will work even if it eventually requires to access the server (for example if the ORDA cache is expired). However, it is highly recommended to make sure that the local function does not access data on the server, otherwise the local execution could not bring any performance benefit. A local function that generates many requests to the server is less efficient than a function executed on the server that would only return the resulting values. For example, consider the following function on the Schools entity class:

// Get the youngest students  
// Inappropriate use of local keyword
local Function getYoungest
	var $0 : Object
    $0:=This.students.query("birthDate >= :1"; !2000-01-01!).orderBy("birthDate desc").slice(0; 5)

without the local keyword, the result is given using a single request
with the local keyword, 4 requests are necessary: one to get the Schools entity students, one for the query(), one for the orderBy(), and one for the slice(). In this example, using the local keyword is inappropriate.

Examples

Calculating age

Given an entity with a birthDate attribute, we want to define an age() function that would be called in a list box. This function can be executed on the client, which avoids triggering a request to the server for each line of the list box.

On the StudentsEntity class:

Class extends Entity

local Function age() -> $age: Variant

If (This.birthDate#!00-00-00!)
    $age:=Year of(Current date)-Year of(This.birthDate)
Else
    $age:=Null
End if

Checking attributes

We want to check the consistency of the attributes of an entity loaded on the client and updated by the user before requesting the server to save them.

On the StudentsEntity class, the local checkData() function checks the Student's age:

Class extends Entity

local Function checkData() -> $status : Object

$status:=New object("success"; True)
Case of
    : (This.age()=Null)
        $status.success:=False
        $status.statusText:="The birthdate is missing"

    :((This.age() <15) | (This.age()>30) )
        $status.success:=False
        $status.statusText:="The student must be between 15 and 30 - This one is "+String(This.age())
End case

Calling code:

var $status : Object

//Form.student is loaded with all its attributes and updated on a Form
$status:=Form.student.checkData()
If ($status.success)
    $status:=Form.student.save() // call the server
End if

Support in 4D IDE

Class files

An ORDA data model user class is defined by adding, at the same location as regular class files (i.e. in the /Sources/Classes folder of the project folder), a .4dm file with the name of the class. For example, an entity class for the Utilities dataclass will be defined through a UtilitiesEntity.4dm file.

Creating classes

4D automatically pre-creates empty classes in memory for each available data model object.

By default, empty ORDA classes are not displayed in the Explorer. To show them you need to select Show all data classes from the Explorer's options menu:

ORDA user classes have a different icon from regular classes. Empty classes are dimmed:

To create an ORDA class file, you just need to double-click on the corresponding predefined class in the Explorer. 4D creates the class file and add the extends code. For example, for an Entity class:

Class extends Entity

Once a class is defined, its name is no longer dimmed in the Explorer.

Editing classes

To open a defined ORDA class in the 4D Code Editor, select or double-click on an ORDA class name and use Edit... from the contextual menu/options menu of the Explorer window:

For ORDA classes based upon the local datastore (ds), you can directly access the class code from the 4D Structure window:

Code Editor

In the 4D Code Editor, variables typed as an ORDA class automatically benefit from autocompletion features. Example with an Entity class variable:

Architecture​

Class Description​

DataStore Class​

Example​

DataClass Class​

Example​

Example with a remote datastore​

EntitySelection Class​

Example​

Entity Class​

Computed attributes​

Alias attributes​

Example​

Specific rules​

Preemptive execution​

Computed attributes​

Overview​

How to define computed attributes​

Function get <attributeName>​

Syntax​

Examples​

Function set <attributeName>​

Syntax​

Example​

Function query <attributeName>​

Syntax​

Examples​

Function orderBy <attributeName>​

Syntax​

Example​

Alias attributes​

Overview​

How to define alias attributes​

Alias <attributeName> <targetPath>​

Syntax​

Using alias attributes​

Alias properties​

Examples​

Exposed vs non-exposed functions​

Example​

onHttpGet keyword​

params​

result​

Example​

Local functions​

Examples​

Calculating age​

Checking attributes​

Support in 4D IDE​

Class files​

Creating classes​

Editing classes​

Code Editor​

Architecture

Class Description

DataStore Class

Example

DataClass Class

Example

Example with a remote datastore

EntitySelection Class

Example

Entity Class

Computed attributes

Alias attributes

Example

Specific rules

Preemptive execution

Computed attributes

Overview

How to define computed attributes

`Function get <attributeName>`

Syntax

Examples

`Function set <attributeName>`

Syntax

Example

`Function query <attributeName>`

Syntax

Examples

`Function orderBy <attributeName>`

Syntax

Example

Alias attributes

Overview

How to define alias attributes

`Alias <attributeName> <targetPath>`

Syntax

Using alias attributes

Alias properties

Examples

Exposed vs non-exposed functions

Example

onHttpGet keyword

params

result

Example

Local functions

Examples

Calculating age

Checking attributes

Support in 4D IDE

Class files

Creating classes

Editing classes

Code Editor