I cant seem to find an acceptable answer to this.
There are two big things I keep seeing: 1) Don't execute queries in the controller. That is the responsibility of business or data. 2) Only select the columns that you need in a query.
My problem is that these two things kind of butt heads since what is displayed in the UI is really what determines what columns need to be queried. This in turn leads to the obvious solution of running the query in the controller, which you aren't supposed to do. Any documentation I have found googling, etc. seems to conveniently ignore this topic and pretend it isn't an issue.
Now if I take it the other way and query everything in the business layer then I implicitly am making all data access closely reflect the ui layer. This is more a problem with naming of query functions and classes than anything I think.
Take for example an application that has several views for displaying different info about a customer. The natural thing to do would be to name these data transfer classes the same as the view that needs them. But, the business or service layer has no knowledge of the ui layer and therefore any one of these data transfer classes could really be reused for ANY view without breaking any architecture rules. So then, what do I name all of these variations of, say "Customer", where one selects first name and last name, another might select last name and email, or first name and city, and so on. You can only name so many classes "CustomerSummary".
I understand that in entity framework I can have a data layer pass back an IQuerable whose execution is deferred and then just tell that IQueryable what fields I want. That is great. It seems to solve the problem. For .NET. The problem is, I also do PHP development. And pretty much all of the ORMs for php are designed in a way that totally defeat the purpose of using an ORM at all. And even those dont have the same ability as EF / IQueryable. So I am back to the same problem without a solution again in PHP.
So, my overall question is how do I get only the fields I need without totally stomping on all the rules of an ntier architecture? And without creating a data layer that inevitably has to be designed to reflect the layout of the UI layer?
And pretty much all of the ORMs for php are designed in a way that totally defeat the purpose of using an ORM at all.
The Doctrine PHP ORM offers lazy loading down to the property / field level. You can have everything done through proxies that will only query the database as needed. In my experience letting the ORM load the whole object once is preferable 90%+ of the time. Otherwise if you're not careful you will end up with multiple queries to the database for the same records. The extra DB chatter isn't worthwhile unless your data model is messy and your rows are very long.
Keep in mind a good ORM will also offer a built-in caching layer. Populating a whole object once and caching it is easier and more extensible then having your code keep track of which fields you need to query in various places.
So my answer is don't go nuts trying to only query the fields you need when using an ORM. If you are writing your queries by hand just in the places you need them, then only query the fields you need. But since you are talking good architectural patterns I assume you're not doing this.
Of course there are exceptions, like querying large data sets for reporting or migrations. These will require unique optimizations.