Help needed regarding Validations

[naveed83]

Hello,
I normally do all the validations (e.g. valid email, digits only etc) on php script when a page is post back to the server, and if all validations are passed then execute the method of the class to save the data. There is no validations done in class itself (in setter methods for public properties). Is this the right thing?

1. what is the best place to run the validations? I mean should it be done in the controller/script or should it be done by the business class itself?
2. Should i do the validations in both script and in class as well?
3. Can anyone provide me some links about best practices for the validations?

Thanks.

[danman]

I think it shuld be done in the business class..

$obj = new Car();
 
$obj->SetVal('x');
 
if($obj->Save()){
//success
 
}else{
//fail
 
$obj->GetErrors()
 
}

The reason is that the object could be changed from different places in the application. There are business rules validation as well as data integretity validation that need to take place..
I am also lookling for a good implementation/best practices for this..

[naveed83]

Right, I also think that validation must also be done in the setter methods for the properties and if any invalid value is passed, it show set some error message.
From you example, I would be doing something like this,
1. Have an array for Error Messages in the class.
2. In the setter method, check for valid data, if any error then add a message in the validation error array. Here we will just set the error message in the array and will move ahead to next action.
3. In my every method of class (like save, update etc), first check the errors array, if it is empty, then perform the actions, else return error array.


Right?

[oddz]

I don't believe its the models responsibility to validate data. Data should be valid before ever changing the models state. Validation is something that is controlled. I believe the models only responsibility is to provide communication between the domain and database. This doesn't include the responsibility of validating data in my opinion.

[AnthonySterling]

I would say, you should have a separate object to validate your object, like so.

$oRedCarColourValidator = new CarColourValidator(array('colour' => 'red'));
$oCar = new Car('red');
if($oRedCarColourValidator->isValid($oCar))
{
    #valid
}
else
{
    echo $oRedCarColourValidator->getError(); #Car is not red.
} 

class Car
{
    protected $sColour;
    
    public function __construct($sColour)
    {
        $this->sColour = $sColour;
    }
    
    public function getColour()
    {
        return $this->sColour;
    }
} 

class CarColourValidator extends Validator
{
    public function isValid($mSubject)
    {
        if($mSubject->getColour() === $this->getOption('colour'))
        {
            return true;
        }
        $this->setError('Car is not red.');
        return false;
    }
} 

abstract class Validator
{
    private $aOptions;

    private $sError = null;

    /**
     *
     * @param Array $aOptions
     */
    public function __construct($aOptions = array())
    {
        $this->aOptions = $aOptions;
    }
    /**
     *
     * @param String $sName
     * @param Mixed $mValue
     */
    public function setOption($sName, $mValue)
    {
        $this->aOptions[$sName] = $mValue;
    }

    /**
     *
     * @param String $sName
     * @return Mixed
     */
    public function getOption($sName)
    {
        return $this->aOptions[$sName];
    }

    /**
     *
     * @param String $sError
     */
    protected function setError($sError)
    {
        $this->sError = $sError;
    }

    /**
     *
     * @return String
     */
    public function getError()
    {
        return $this->sError;
    }

    abstract public function isValid($mSubject);
} 

[fristi]

I have done something similar to what oddz is describing. I made a class which validates and does some needed processing on Form Data. When everything is correct the class can output all the data (stored in arrays). This data will then be passed on to a query manager which will save it to a database.

[naveed83]

Let just say I am not using any MVC framework, just a PHP file with a form and server script and a business class (e.g. Users class). On my php page, I just creates an object of user class, sets it properties and calls the save method.
Now where to validate the data? Before passing to the object or inside the setter methods?
Please note that i also need to show the error message to the user as well.

[oddz]

I don't think its wrong to validate whether or not data is compatible with the model field data type. However, string matching type validation is outside the responsibility of the model. So checking whether data is compatible with a varchar(15) would be alright for a user name perhaps. However, checking that the user name doesn't contain any spaces and has at least one alphabetic character is more or less a controller level constraint.

[Mastodont]

naveed83:
validation must also be done in the setter methods for the properties
How would you in this case check dependencies between different properties, if first setter is called?

Now where to validate the data? Before passing to the object or inside the setter methods?
I vote for separate method, after passing to object.

if ( $model->Validate($array) ) {
   $model->Save(); // Validate can store $array internally
} else {
  $errors = $model->GetValidationErrors();
} 

oddz:string matching type validation is outside the responsibility of the model
Could you please elaborate on this? Do you want to put validation routines into controller?

[kyberfabrikken]

Trying to isolate "validation" as a separate concept, doesn't work that well, IMHO. Some would fit best in the model layer. Some would fit in the storage (database), some would fit in the controller layer, and some could be pushed all the way out to the view layer.

[danman]

Now where to validate the data? Before passing to the object or inside the setter methods?
Please note that i also need to show the error message to the user as well.

Validating every "Set" method would become tedious, since it could be many Set calls..

I don't think its wrong to validate whether or not data is compatible with the model field data type. However, string matching type validation is outside the responsibility of the model. So checking whether data is compatible with a varchar(15) would be alright for a user name perhaps. However, checking that the user name doesn't contain any spaces and has at least one alphabetic character is more or less a controller level constraint.

Not knowing much about the MVC paradigm, how would you handle
changes to the model from different places ?
Lets say you want to change username from a different view than a registration page or similar, would'nt that string validation be in two different controllers?

[FrlB]

1. what is the best place to run the validations? I mean should it be done in the controller/script or should it be done by the business class itself?
2. Should i do the validations in both script and in class as well?
3. Can anyone provide me some links about best practices for the validations?

In my opinion this depends on the validation type.
1. Validating input on the request level, no business logic involved - e.g. missing parameter or parameters changing the application flow - can be validated in the controller.
2. Validation involving business logic should be handled in your model. Now depending on your layering:
- The database should make use of data constraints to prevent invalid entries.
- The model class itself should not allow invalid properties, this catches more than the db constraints.
- More complicated validation requiring various model classes should be handles in a service layer above those.

[oddz]

oddz:string matching type validation is outside the responsibility of the model
Could you please elaborate on this? Do you want to put validation routines into controller?

Whether or not a string matches particular pattern is no concern to the model. However, checking whether that the data can be inserted as the specified type is. So making sure that a string isn't over 15 characters for varchar(15) is the models responsibility. However, checking whether certain characters exist is a lower level validation that doesn't really matter on the model level. The model just cares that the data can be inserted. Where as the controller cares that is formatted in the correct matter.

Not knowing much about the MVC paradigm, how would you handle
changes to the model from different places ?
Lets say you want to change username from a different view than a registration page or similar, would'nt that string validation be in two different controllers?

Well the whole idea is to isolate that responsibility to one place (controller).

[oddz]

validation must also be done in the setter methods for the properties

The problem with this is the unnecessary validation that will occur when filling containers with data from a result set. Given 100 rows of data being converted to objects that is 100 unnecessary processes. If the data where invalid it wouldn't be in the database.

[Mastodont]

oddz:
The model just cares that the data can be inserted. Where as the controller cares that is formatted in the correct matter.
It sounds like you take model only as database layer and business rules should reside in controller. This is IMHO incorrect.

[AnthonySterling]

Where as the controller cares that is formatted in the correct matter.

Forgive my ignorance (because that's what it is ), but wouldn't this be violating the Single Responsibility Principle?

If this was simply a matter of have 3 objects, a model, view and a controller I guess it could be arguable - but shouldn't the controller, just well, control?

Again, I'm not really au fair with OOP, but would you not just wrap a validation object around the insertion model?

Anthony.