Yii2: How to set default attribute values in ActiveRecord?

问题

This may seem like a trivial question, however all of the obvious solutions that I can think of have their own flaws.

What we want is to be able to set any default ActiveRecord attribute value for new records only, in a way that makes it readable before and during validation and does not interfere with derived classes used for search.

The default values need to be set and ready as soon as we instantiate the class, so that (new MyModel)->attr returns the default attr value.

Here are some of the possibilities and the problems they have:

A) In MyModel override the init() method and assign default value when isNewRecord is true like so:
```
public function init() {
    if ($this->isNewRecord) {
        $this->attr = 'defaultValue';
    }
    parent::init();
}
```
Problem: Search. Unless we explicitly unset our default attribute in MySearchModel (very error-prone because it is too easy to forget), this will also set the value before calling search() in the derived MySearchModel class and interfere with searching (the attr attribute will already be set so search will be returning incorrect results). In Yii1.1 this was resolved by calling unsetAttributes() before calling search(), however no such method exists in Yii2.
B) In MyModel override the beforeSave() method like so:
```
public function beforeSave($insert) {
    if ($insert) {
        $this->attr = 'defaultValue';
    }
    return parent::beforeSave();
}
```
Problem: Attribute is not set in unsaved records. (new MyModel)->attr is null. Worse yet, even other validation rules that rely on this value will not be able to access it, because beforeSave() is called after validation.
C) To ensure the value is available during validation we can instead override the beforeValidate() method and set the default values there like so:
```
public function beforeValidate() {
    if ($this->isNewRecord) {
        $this->attr = 'defaultValue';
    }
    return parent::beforeValidate();
}
```
Problem: Attribute is still not set in unsaved (unvalidated) records. We need to at least call $model->validate() if we want to get the default value.

D) Use DefaultValidator in rules() to set a default attribute value during validation like so:

public function rules() {
    return [
        [
            'attr', 'default',
            'value' => 'defaultValue',
            'on' => 'insert', // instantiate model with this scenario
        ],
        // ...
    ];
}

Problem: Same as B) and C). Value is not set until we actually save or validate the record.

So what is the right way to set default attribute values? Is there any other way without the outlined problems?

回答1:

This is a hangup with Yii's bloated multi-purpose ActiveRecords

In my humble opinion the form models, active records, and search models would be better off split into separate classes/subclasses

Why not split your search models and form models?

abstract class Creature extends ActiveRecord {
    ...
}

class CreatureForm extends Creature {

    public function init() {
        parent::init();
        if ($this->isNewRecord) {
            $this->number_of_legs = 4;
        }
    }
}

class CreatureSearch extends Creature {

    public function search() {
        ...
    }
}

The benefits of this approach are

You can easily cater for different validation, set up and display cases without resorting to a bunch of ifs and switches
You can still keep common code in the parent class to avoid repetition
You can make changes to each subclass without worrying about how it will affect the other
The individual classes don't need to know about the existence of any of their siblings/children to function correctly

In fact, in our most recent project, we are using search models that don't extend from the related ActiveRecord at all

回答2:

There's two ways to do this.

$model => new Model();

Now $model has all the default attributes from the database table.

Or in your rules you can use:

[['field_name'], 'default', 'value'=> $defaultValue],

Now $model will always be created with the default values you specified.

You can see a full list of core validators here http://www.yiiframework.com/doc-2.0/guide-tutorial-core-validators.html

回答3:

I know it is answered but I will add my approach. I have Application and ApplicationSearch models. In Application model I add init with a check of the current instance. If its ApplicationSearch I skip initializations.

    public function init()
    { 
        if(!$this instanceof ApplicationSearch)  
        {
            $this->id = hash('sha256',  123);
        }

        parent::init();
    }

also as @mae commented below you can check for existence of search method in current instance, assuming you didn't add any method with name search to the non-search base model so the code becomes:

    public function init()
    { 
        // no search method is available in Gii generated Non search class
        if(!method_exists($this,'search'))  
        {
            $this->id = hash('sha256',  123);
        }

        parent::init();
    }

回答4:

I've read your question several times and I think there are some contradictions.
You want the defaults to be readable before and during validation and then you try init() or beforeSave(). So, assuming you just want to set the default values in the model so they can be present during the part of the life cycle as long as possible and not interfere with the derived classes, simply set them after initialising the object.

You can prepare separate method where all defaults are set and call it explicitly.

$model = new Model;
$model->setDefaultValues();

Or you can create static method to create model with all default values set and return the instance of it.

$model = Model::createNew();

Or you can pass default values to constructor.

$model = new Model([
    'attribute1' => 'value1',
    'attribute2' => 'value2',
]);

This is not much different from setting the attributes directly.

$model = new Model;
$model->attribute1 = 'value1';
$model->attribute2 = 'value2';

Everything depends on how much transparent would you like your model be to your controller.

This way attributes are set for the whole life cycle except the direct initialisation and it's not interfering with derived search model.

回答5:

Just override __construct() method in your model like this:

class MyModel extends \yii\db\ActiveRecord {

    function __construct(array $config = [])
       {
           parent::__construct($config);
           $this->attr = 'defaultValue';
       }
    ...
}

回答6:

You can prepare separate method where all defaults are set and call it explicitly.

$model = new Model;
if($model->isNewRecord())
    $model->setDefaultValues();

来源：https://stackoverflow.com/questions/39314213/yii2-how-to-set-default-attribute-values-in-activerecord

标签

activerecord

yii2

yii2-model

yii2-validation