type_guesser

.. index::

single: Forms; Custom Type Guesser

Creating a Custom Type Guesser

The Form component can guess the type and some options of a form field by

using type guessers. The component already includes a type guesser using the

assertions of the Validation component, but you can also add your own custom

type guessers.

.. sidebar:: Form Type Guessers in the Bridges

Symfony also provides some form type guessers in the bridges. These can be

used if you use that library.

* :class:`Symfony\\Bridge\\Propel1\\Form\\PropelTypeGuesser` provided by

the Propel1 bridge;

* :class:`Symfony\\Bridge\\Doctrine\\Form\\DoctrineOrmTypeGuesser`

provided by the Doctrine bridge.

A PHPDoc Type Guesser

In this section, you are going to build a PHPDoc type guesser. At first, you

need to create a class which extends

:class:`Symfony\\Component\\Form\\FormTypeGuesserInterface`. This interface

requires 4 methods:

* :method:`Symfony\\Component\\Form\\FormTypeGuesserInterface::guessType` -

tries to guess the type of a field;

* :method:`Symfony\\Component\\Form\\FormTypeGuesserInterface::guessRequired` -

tries to guess the value of the ``required`` option;

* :method:`Symfony\\Component\\Form\\FormTypeGuesserInterface::guessMaxLength` -

tries to guess the value of the ``max_length`` option;

* :method:`Symfony\\Component\\Form\\FormTypeGuesserInterface::guessPattern` -

tries to guess the value of the ``pattern`` option.

The most basic class looks like::

Guessing the Type

When guessing a type, the method returns either an instance of

:class:`Symfony\\Component\\Form\\Guess\\TypeGuess` or nothing, to determine

that the type guesser cannot guess the type.

The ``TypeGuess`` constructor requires 3 options:

* The type name (one of the :doc:`form types </reference/forms/types`);

* Additionally options (for instance, when the type is ``entity``, you also

want to set the ``class`` option). If no types are guessed, this should be

set to an empty array;

* The confidence that the guessed type is correct. This can be one of the

constants of the :class:`Symfony\\Component\\Form\\Guess\Guess` class:

``LOW_CONFIDENCE``, ``MEDIUM_CONFIDENCE``, ``HIGH_CONFIDENCE``,

``VERY_HIGH_CONFIDENCE``. After all type guessers are executed, the type

with the highest confidence is used.

With this knowledge, you can easily implement the ``guessType`` method of the

``PHPDocTypeGuesser``::

This type guesser can now guess the field type for a property if it has

PHPdoc!

Guessing Field Options

The other 3 methods (``guessMaxLength``, ``guessRequired`` and

``guessPattern``) return a :class:`Symfony\\Component\\Form\\Guess\\ValueGuess`

instance with the value of the option. This constructor has 2 arguments:

* The value of the option;

* The confidence that the guessed value is correct (using the constants of the

``Guess`` class).

``null`` is guessed when you believe the value of the option should not be

set.

.. caution::

You should be very careful with the ``guessPattern`` method. When the

type is a float, you cannot use it to determine a min or max value of the

float (e.g. you want a float to be greater than ``5``, ``4.512313`` is not valid

but ``length(4.512314) > length(5)`` is, so the pattern will success). In

this case, the value should be set to ``null`` with a ``MEDIUM_CONFIDENCE``.

* :doc:`/components/form/type_guesser`