Add a filter to select specific fields

[dunglas]

http://example.com/books?fields=title,description should serialize only the specified properties.

The filter should not be Doctrine dependent. It must implement the FilterInterface (to appear in the documentation) and decorate the SerializerContextBuilder to use the new attributes context option available in Symfony 3.3.

This filter should throw an exception if the Serializer version is < to 3.3.

[meyerbaptiste]

How does this feature deal with serialization groups @dunglas?

[dunglas]

In the Symfony serializer, groups are applied first, then fields are applied. A field cannot be serialized if it is hidden by a group. I think we must respect this behavior.

[bwegrzyn]

Would this work with nested properties? For example ?fields=user.email

[dunglas]

Yes, the Symfony serializer supports this.

[mitalcoi]

Great feature, but maybe we should to avoid using key names without "_" prefix?
It will be more safe design:
http://example.com/books?_fields=title,description
It is also related to #1082
http://example.com/books?_groups=group1,group2

[dunglas]

Existing keys such as page are not prefixed. We cannot use this convention now, it would not be consistent. However all keys are already configurable. It will be the same for this one.

[Simperfit]

This has been merged