The Definitive Guide to Validation in Craft, Part 2: Attributetypes

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The first instalment of this series provided a high-level overview of validation in Craft. We covered what happens behind the scenes when Craft validates your model, which model validation methods are available (and what each one does), and how to define your model attributes.

This instalment is all about Craft’s AttributeTypes: what they are, what they do, and which ones are available.

What is an AttributeType?

Every model attribute must have a type, expressed in the form AttributeType::TypeName. For example, the following code tells Craft that the age attribute is a number.

    'age' => [
        'type' => AttributeType::Number,

In practice these AttributeTypes are simply class constants, defined in craft/app/enums/AttributeType.php. You could, if you were so inclined, substitute each constant for its associated string representation, and everything would continue to work as normal.1

The many roles of AttributeTypes

AttributeTypes are used in a number of locations throughout Craft, and serve several purposes. This article is concerned with how AttributeTypes affect model validation, but you should at least be aware of the other roles that AttributeTypes have to play.

Normalising data

Both the DateTime and Mixed AttributeTypes normalise the data assigned to the associated model attribute.

  • AttributeType::DateTime accepts either a DateTime object or a valid timestamp. If you choose to assign a timestamp, it will be converted to a DateTime object;
  • If you assign a JSON string to an AttributeType::Mixed attribute, it will be converted to an array.

Defining database columns

When used in the context of a record, an AttributeType declaration defines the database column used to store the attribute.

If you decide to override a default model AttributeType parameter for the purposes of validation (for example, by increasing the maxLength), you should take care to modify the associated record attribute.

“Packaging” and “de-packaging” data for storage

When a record is saved to the database, the AttributeType will convert its value into a format suitable for storage within the database. The same process happens in reverse when retrieving data from the database.

How do AttributeTypes affect validation?

As you will recall from part 1, when you call the validate method on your model, Craft translates your attribute definitions into Yii-compatible validation rules.

This doesn’t just apply to explicit validation rules such as min and max, it also applies to AttributeTypes. You can think of an AttributeType as being a convenient way of telling Craft to apply a predefined set of validation rules to your attribute.

For example, behind the scenes Craft translates our age attribute definition into the following Yii-compatible validation rules:

        'min'         => -2147483648,
        'max'         => 2147483648,
        'integerOnly' => true,

This automatic translation of an AttributeType into zero or more Yii-compatible validation rules is the reason you can’t define your own custom AttributeType.2. It is also how Craft determines which validator class to use when verifying the attribute value.

The validator class can be:

  1. A built-in Yii validator class, such as CBooleanValidator;
  2. A custom Craft validator class, such as DateTimeValidator;
  3. Your own custom validator method or class (we’ll get to this in a later instalment on more advanced validation techniques).

Which validator class is used is important because some accept additional parameters or constraints, which are implicitly set by the AttributeType, but which you may override if necessary.

Overriding the default validator parameters

There are two ways to override the validator parameters which are automatically set by the AttributeType: the easy but limited way, and the flexible but advanced way.

The easy but limited way simply involves using one of the built-in Craft validation rules. For example, AttributeType::ClassName specifies that the attribute value be no longer than 150 characters. We can easily override this by setting the maxLength rule:

    'myClass' => [
        'type'      => AttributeType::ClassName,
        'maxLength' => 100,

The downside of this technique is that it can only override a very limited subset of the automatically-generated validation rules. Furthermore, this approach cannot be used to override the built-in validation class defaults.

The flexible but advanced approach suffers from none of these limitations. However, it is a little more involved, so we’ll cover it in a later instalment, dedicated to more advanced validation techniques.

Available AttributeTypes

Craft defines 17 AttributeTypes, each of which is described below. For each AttributeType, I have included:

  1. A description of the type of validation implicitly defined by the AttributeType;
  2. The validator class used to perform the validation;
  3. Where applicable, those Craft validation rules which may be used to override the AttributeType defaults.


AttributeType::Bool uses the Yii CBooleanValidator class to validate that the attribute value is a boolean.

You may override the maxLength validation rule, but there is no reason why it would make sense to do so.


AttributeType::ClassName uses the Yii CStringValidator class to validate that the attribute value is a string with a maximum length of 150 characters.

You may override the maximum length constraint using the maxLength validation rule.

     'maxLength' => 100,  // Default is 150


AttributeType::DateTime uses the Craft DateTimeValidator class to validate that the attribute value is a valid date. The value will pass validation if it is:

  1. An instance of the DateTime class;
  2. A valid timestamp, as determined by the Craft DateTimeHelper class.


AttributeType::Email uses the Yii CEmailValidator class to validate that the attribute value is a valid email address, with a minimum length of 5 characters, and a maximum length of 254 characters.

Email validation is performed using a regular expression.

You may override the minimum length constraint using the minLength validation rule. However, you cannot override the maximum length constraint, as it is hard-coded in the validator class.3.

    'minLength' => 15,  // Default is 5


AttributeType::Enum uses the Yii CRangeValidator class to validate that the attribute value exists in the array of values specified by the values key in the attribute definition.4

That’s quite a mouthful, so here’s an example:

'color' => [
    'type' => AttributeType::Enum,
    'values' => ['R', 'G', 'B'],

In the above example, the attribute will pass validation only if its value is “R”, “G”, or “B”.


AttributeType::Handle uses the Craft HandleValidator class to validate that the attribute value:

  1. Is a valid “handle”;
  2. Is not a reserved word;
  3. Does not exceed 255 characters.

So what constitutes a valid handle? Here are the exact rules, as defined by the HandleValidator regular expression. A handle:

  • Must start with a letter;
  • Must be at least one character in length;
  • Must contain only alpha-numeric characters, or the underscore character (_).

It’s worth noting that a handle may not contain a hyphen (-).

As mentioned above, in order to pass validation the handle must not be a reserved word. Here is the default list of reserved words:

  • attribute
  • attributes
  • attributeLabels
  • attributeNames
  • classHandle
  • content
  • dateCreated
  • dateUpdated
  • false
  • fields
  • handle
  • id
  • n
  • name
  • no
  • rawContent
  • rules
  • section
  • this
  • true
  • uid
  • y
  • yes

It is not possible to override the list of reserved words. However, you may supplement it, by specifying the reservedWords key in your attribute definition. You may also override the maximum string length.

    'maxLength'     => 150,
    'reservedWords' => ['Bob', 'Kate', 'Wibble'],


AttributeType::Locale uses the Craft LocaleValidator class to validate that the attribute value is a known locale for the current site (for example, “en_us”).

Specifically, the LocaleValidator checks whether the attribute value appears in the array of site locales returned by the craft()->i18n->getSiteLocaleIds() method.


AttributeType::Mixed does not apply any validation rules.


AttributeType::Name uses the Yii CStringValidator class to validate that the attribute value is a string with a maximum length of 255 characters.

You may override the maximum length constraint using the maxLength validation rule.

     'maxLength' => 100,  // Default is 255


AttributeType::Number uses the Yii CNumberValidator class to validate that the attribute value is an integer, with a minimum value of -2147483648, and a maximum value of 2147483648.

As you might expect, you may override both the minimum and maximum values. You may also instruct the validator to accept non-integers values, by assigning a positive integer to the decimals key.

    'min'      => 0,     // Default is -2147483648
    'max'      => 1024,  // Default is 2147483648
    'decimals' => 1,     // Disables the "integerOnly" rule


AttributeType::Slug does not apply any validation rules.5


AttributeType::SortOrder does not apply any validation rules.6


AttributeType::String does not apply any validation rules.


AttributeType::Template uses the Yii CStringValidator class to validate that the attribute value is a string with a maximum length of 500 characters.

You may override the maximum length constraint using the maxLength validation rule.

     'maxLength' => 250,  // Default is 500


AttributeType::Url uses the Craft UrlValidator class to validate that the attribute value is a valid URL. Behind the scenes, it overrides the Yii CUrlValidator class, to add support for protocol-relative URLs.

So what constitutes a valid URL in this case? Rather than attempting to describe the UrlValidator regular expression using a series of bullet points7, here are some examples of URLs which Craft considers valid.

//                       # No schema                  # HTTP                 # HTTPS                 # Optional trailing slash        # Sub-section(s)         # Sub-domain(s)       # Username in URL  # Username and password in URL

So far, so predictable. However, it’s worth noting that the following less conventional URLs will also pass validation.



AttributeType::UrlFormat uses the Craft UrlFormatValidator class. It does not perform any validation, but does directly modify the attribute value, by removing any leading or trailing forward-slashes.8


AttributeType::Uri uses the Craft UriValidator class to validate that the attribute value is a valid URI.

So what constitutes a valid URI? Here are the exact rules, as defined by the UriValidator regular expression. A URI:

  • Must be at least one character in length;
  • Must not contain any whitespace characters.


And so we come to the end of another mammoth instalment. You should now know everything worth knowing about AttributeTypes: what they are, which ones are available, and how they affect model validation.

You may have noticed that, along the way, we made quite a few references to Craft’s built-in validation rules, without ever defining which rules are available, or what they do.

We’ll rectify that in the next instalment of “The Definitive Guide to Validation in Craft”, so don’t forget to check back at the same time next week (or just subscribe to our newsletter).

  1. Don’t do this. ↩︎

  2. Technically you could, because it’s just a string value. However, Craft wouldn’t know what to do with it, so there’s no point. ↩︎

  3. If you examine the Yii-compatible validation rules generated by Craft, you will notice that the maximum string length is set to 255 (['max' => 255]). This value is both redundant (it cannot be overridden), and incorrect (the maximum length is actually 254 characters). ↩︎

  4. The CRangeValidator class can also validate that a value is not in the range of given values. This is not supported by Craft. ↩︎

  5. Surprisingly. ↩︎

  6. That’s not entirely true. AttributeType::SortOrder currently uses the Yii CStringValidator class to validate that the attribute value is a string with a maximum length of 4 characters. However, my understanding is that this is not the intended behaviour, and may soon be “fixed”. ↩︎

  7. I tried this. You end up with a very long list which is far less comprehensible than the original regular expression. ↩︎

  8. Having trimmed the forward-slashes, the UrlFormatValidator class checks its public requireSlug property, to determine whether to validate the value. This property is set to false by default, and cannot be overridden via the Craft validation rules, hence no validation is carried out. ↩︎

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