Proposal for accessing populated relations

[cebe]

fixes #842

• allows checking whether a relation has been populated
• getting a list of relation names that have been populated
• getting all populated relation data

todo:

• add phpdoc

[coveralls]

Coverage remained the same when pulling 90839ce on cebe:842-relation-data into d8b94d6 on yiisoft:master.

[qiangxue]

What are the use cases for getPopulatedRelationNames() and getPopulatedRelations()?

[cebe]

Use case for getPopulatedRelations() is described in #842 don't have a use case for the names only right now.

[qiangxue]

Perhaps it's better to turn _related into protected or public, and rename it to relatedRecords.

[cebe]

There is a problem with storing them with lower case name. They should be available as their original methods name in camel case.

[qiangxue]

Agree. We can remove strtolower() call.

[coveralls]

Coverage decreased (-0.17%) when pulling a23c54a on cebe:842-relation-data into d8b94d6 on yiisoft:master.

[coveralls]

Coverage remained the same when pulling 0bc8cbf on cebe:842-relation-data into d8b94d6 on yiisoft:master.

[cebe]

I'd prefer to have the methods instead of public property as they allow to get overriden and to interact with the process of populating and getting relational data.
What do you think @qiangxue ?

[qiangxue]

Looks good to me. Thanks.