Validatable

Adds validation capabilities for attributes to a class it is mixed into. It works together with the 'attributable' library and you should first mix Attributable module into the class before mixing in this one. Then define attributes and only after that define validations for them.

Validations work much the same way as they do in the Ruby On Rails framework. When the validate() method is called, it looks at all the attributes mentioned in the validations Map in your class and check if they pass the defined validations. If not, errors are added into the validation_errors Map.

IMPORTANT: please don't forget to check with the documentation for the 'attributable' library before using this one.

Usage example

Mix the Validatable module into your class, and make sure Attributable is also mixed in before it:
```
 class Employee extends Object with Attributable, Validatable {}
```

Define attributes using the attribute_names instance variable (attributable library feature):

 class Employee extends Object with Attributable, Validatable {
   final List attribute_names = ['first_name', 'family_name', 'age', 'sex', 'email'];
 }

Define validations for these attributes:

 class Employee extends Object with Attributable, Validatable {
    
   final List attribute_names = ['first_name', 'family_name', 'age', 'sex', 'email'];
   
   final Map validations = {
      
     'first_name'  : { 'isShorterThan' : 30,     'isLongerThan' : 1  },
     'family_name' : { 'isShorterThan' : 50,     'isLongerThan' : 2  },
     'age'         : { 'isNumeric'     : true,   'isMoreThan'   : 18 },
     'sex'         : { 'isOneOf' : ['f', 'm'],   'isNotEmpty' : true },
     
     'email' : { 'matches' : { 'value': new RegExp(r"@"), 'message' : 'this isn\'t an email, bro' }}
     
   };
   
 }

Create a new instance of your class, set attribute values on it and run the validate() method:

 var employee = new Employee();
 employee.first_name  = "Vincent";
 employee.family_name = "Vega";
 employee.validate();

See what the validation errors contain:
```
 print(employee.validation_errors);
```

You can find and run this example in the /example/employee_validations.dart. Don't hesitate to play with various validations and attribute values.

Defining a validation

A validation in the validations Map consists of the following parts:

[String attribute_name]: { [String validation_name] : [validation_argument] }

An attribute_name is simply the name of the attribute that is being validated.

A validation_name is the name of the validation that is being applied to it (for a list of all available validations, see section "List of available validations" of this README).

A validation_argument can be anything that this particular validation accepts: a String, a number or a List (for instructions on what type of agruments are accepted for which validations, see section "List of available validations" of this README)

Any validation can accept a Map as a validation_argument. In that case, the actual validation argument should move under the value key of that Map. There is another key in this Map that may be used called message. It allows you to specify a custom message for the cases in which the validation would fail. From the example above:

'email' : { 'matches' : { value: new RegExp(r"@"), 'message' : 'this isn't an email, bro' }}

We had to write it this way in order to specify a custom message. If we didn't need a custom message, we could've written this validation like this:

'email' : { 'matches' : new RegExp(r"@") }

Custom validation functions

You can define a custom validation function to check whatever conditions you desire:

final Map validations = {
  'email' : { 'function' : { 'name': 'validateEmail', 'message': "doesn't look like an email" }}
};

prvt_validateEmail() => this.email.contains("@");

If the function returns false, it means the validation didn't pass and an error message is added. You can also pass a custom object on which the function will be called. This is useful when you want to have your validation function in a separate object:

class MyValidator {
  validateEmail() => this.email.contains("@");
}

var obj = new MyVlaidator();

...

final Map validations = {
  'email' : { "object": obj, 'function' : { 'name': 'validateEmail', 'message': "doesn't look like an email" }}
};

List of available validations and their descriptions

isNumeric
- Attribute type: String or num
- Argument: Boolean
- Behavior : checks whether the value only contains numbers from 0-9. It doesn't matter if the actual type of the attribute value is String, rather it's important that this string contains only numbers.
isLessThen
- Attribute type: num
- Argument: num
- Behavior: checks whether the value is less than a certain number.
isMoreThen
- Attribute type: num
- Argument: num
- Behavior: checks whether the value is more than a certain number.
isOneOf
- Attribute type: any
- Argument: List
- Behavior: checks whether the value is present in the List passed as an argument.
isNotOneOf
- Attribute type: any
- Argument: List
- Behavior: checks whether the value is NOT present in the List passed as an argument.
isLongerThan
- Attribute type: String
- Argument: num
- Behavior: checks whether the value is longer than the specified number of charcaters.
isShorterThan
- Attribute type: String
- Argument: num
- Behavior: checks whether the value is shorter than the specified number of charcaters.
hasExactLengthOf
- Attribute type: String
- Argument: num
- Behavior: checks whether the value has the exact length specified in the passed argument.
matches
- Attribute type: String
- Argument: RegExp
- Behavior: checks whether the value matches the RegExp passed as an argument.
isNotNull
- Attribute type: any
- Argument: Boolean
- Behavior: checks whether the value is not null.
isNotEmpty
- Attribute type: String
- Argument: Boolean
- Behavior: checks whether the value is not empty (ignores if it's null).

snitko/dart-validatable

Validatable

Usage example

Defining a validation

Custom validation functions

List of available validations and their descriptions