changeColumn() defaulting.

[dereuromark]

Implement cakephp/phinx#123 in a BC way.

  // NEW WAY - Simple and safe!
  $table->updateColumn('email', null, ['null' => true]);

  // OLD WAY - Still works!
  $table->changeColumn('email', 'string', [
      'null' => true,
      'default' => 'test',
      'limit' => 255,
  ]);

An alternative way, if we want more speaking API, could be

• updateColumnAttributes(field, array options) if we are only interested in changing attributes

[Copilot]

Pull Request Overview

This PR introduces a new updateColumn() method for safer column modifications that preserves unspecified attributes by default, while maintaining backward compatibility with the existing changeColumn() method. The changeColumn() method is updated to support optional attribute preservation via a preserve_unspecified flag and now accepts null as the column type to preserve the existing type.

• Adds updateColumn() as the recommended method for column modifications with automatic attribute preservation
• Enhances changeColumn() to support null type parameter and optional attribute preservation
• Implements comprehensive test coverage for both methods and their preservation behavior

Reviewed Changes

Copilot reviewed 3 out of 3 changed files in this pull request and generated 1 comment.

File	Description
src/Db/Table.php	Adds updateColumn() method, updates changeColumn() to support null type and preservation logic, adds mergeColumnOptions() helper
tests/TestCase/Db/Adapter/MysqlAdapterTest.php	Adds comprehensive test cases for column update/change preservation behavior
docs/en/writing-migrations.rst	Documents both updateColumn() (recommended) and changeColumn() methods with examples

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[LordSimal]

as long as schema reflection represents the column properly I don't see a problem supporting this kind of functionality.

[markstory]

How does one remove length with this API?

[dereuromark]

To remove a length constraint using this API, you would typically need to explicitly set 'length' => null or 'limit' => null in the options array when calling updateColumn(). For example:

 $table->updateColumn('my_column', 'text', ['length' => null]);

I added a test case that shows it works, but from the code above I also see that using isset() instead of array_key_exists() would not set it from the options.