Validations for SQLAlchemy

SQLAlchemy validations is an easy way to be sure that no inconsistent data will be saved to your database. It is a new extension for SQLAlchemy that checks if an object is consistent according to a customizable set of rules just before being saved to the database.

Example

You have a Person class:

class Person(object):
    def __init__(self, name, phone, age):
        self.name = name
        self.phone = phone
        self.age = age

    def __repr__(self):
        return "<Person('%s','%s','%d')>" % (self.name, self.phone, self.age)

Now, we will map it to a person_table (declaration of person_table omitted. See SQLAlchemy docs for more about mapping):

mapper(Person, person_table,
       extension=[
                  Validator(range_of('age', 0, 150))
                 ]
      )

The mapper call above is specifying a range validator for the age attribute of Person. Now, if you try to save a Person with age outside of range 0-150 it will raise a ValidationException and no data will be saved:

>>> p = Person('Foobar', '0123456789', 1000) # age = 1000
>>> session.save(p)
>>> session.flush()

(traceback omitted)

<class 'sqlalchemy_validators.ValidationException'>: Range validation of field "age" of instance of class "Person" failed! Person.age = 1000 (min=0, max=150)

You can also add a second validation:

mapper(Person, person_table,
       extension=[Validator(
                            range_of('age', 0, 150),
                            format_of('phone', re.compile(r'\d{4}-?\d{4}'))
                           )
                 ]
      )

The mapper call adds a second validation to Person class. Now its phone attribute must match the format specified by the regular expression.

Using Elixir

Elixir validations are similar to SQLAlchemy validations, but use a syntax similar to Ruby on Rails ActiveRecord.

The class below implements the same validations of the previous example, but using Elixir.

class Person(Entity):
    name  = Field(Text)
    phone = Field(Text)
    age   = Field(Integer)
        
    validates_format_of('phone', re.compile(r'\d{4}-?\d{4}'))
    validates_range_of('age', 0, 150)

Creating new validators

sqlalchemy-validations is extensible. You can create new validations, inheriting from Validation class in sqlalchemy_validations.py. Take a look at classes FieldFormatValidation and FieldPresenceValidation. They should serve as good examples of how to create your own validations.