TimestampBehavior does not work because of failing validation - validation

Question

I have the following class with a TimestampBehaviour:
/**
* #property int $id
* #property string $name
* #property int $created_at
*/
class Workspace extends yii\db\ActiveRecord {
public static function tableName() {
return 'workspace';
}
public function behaviors() {
return [
[
'class' => TimestampBehavior::className(),
'attributes' => [
ActiveRecord::EVENT_BEFORE_INSERT => 'created_at',
ActiveRecord::EVENT_BEFORE_UPDATE => false,
],
'value' => date('Y-m-d H:i:s')
],
];
}
...
}
For some reason the behavior does not populate the property. It is always empty when I try to save the model ($workspace->save()). I cannot save it since validation fails ("created_at cannot be blank"). There is nothing special with this class. Nothing is overridden. What could be the problem?

Answer 1

It turned out that the validation rules caused the troubles. Unexpected, since I thought all is correct. These were my rules:
public function rules() {
return [
[['id', 'name', 'created_at'], 'required'],
[['id'], 'int'],
[['name'], 'string', 'max' => 100],
[['created_at' ], 'datetime'],
];
}
created_at must not be required - that was the problem.
It is even documented:
Because attribute values will be set automatically by this behavior,
they are usually not user input and should therefore not be validated,
i.e. created_at and updated_at should not appear in the rules() method
of the model.
When $workspace->save() gets executed then the first step is the validation. And only after that step the EVENT_BEFORE_INSERT/EVENT_BEFORE_UPDATE gets triggered which causes TimestampBehaviour to populate the specified fields. And this happens only if the validation was successful! (if you var_dump you will indeed see an empty created_at.) Too late, validation has taken place already and I've got the validation error.
Recommended solution is to remove created_at from the required rule. Other approaches are also possible, of course (e.g. turn off validation or pass the properties that should be validated when save() gets called).

Answer 2

Add behaviour like bellow
public function behaviors()
{
return [
[
'class' => TimestampBehavior::className(),
'createdAtAttribute' => 'create_time',
'updatedAtAttribute' => 'update_time',
'value' => new Expression('NOW()'),
],
];
}
and add it to safe records in your model class.
public function rules()
{
return array(
array('create_time,update_time', 'safe'),
);
}