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I have studied some persistence frameworks mainly Hibernate, DORM, TMS Aurelius and I'm wondering. In a model of type:

TOrderFiscal < > ----- > Items < > -------- > TOrderItem ------- > TProduct

TOrderFiscal --------- > TSuplier --------- > TCidade -------- > State

Each class of this with countless attributes, all mapped correctly to their corresponding tables and fields. When carrying a note without using "Lazy Load" would always be done with several joins select all fields to come from each of these classes.

But it would be a waste since the note need only the supplier code and name attributes, the attributes OrderItem need only code, qty name. stock.

What solution should be taken to create a specific class supplier of note just with these attributes ? eg

TOrder <> ----- > Items <> -------- > TOrderItem ------- > TNotaItemProduct

TOrder -------- > TOrderSupplier

If this is the solution , what happens when a business rule in TProduct should also be TOrderItemProduct? I duplicate code in both classes? Do heritage, eg TORderItemProduct and TProduct both inheriting from TBaseProduct ?

Or is this a concern that we programmers we should not have ?

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1  
This is one of the reasons I do not like ORM frameworks. –  Brandon Apr 12 at 17:29
    
@Brandon The problem is not the ORM the problem is how its being used. Domain objects should not be mapped to a db using an ORM. –  Andy Apr 12 at 19:58
4  
@Andy: I thought that was kinda the whole point of an ORM. –  Robert Harvey Apr 13 at 13:55
1  
@RobertHarvey It depends on who you ask. For trivial apps sure, but for more complex apps mapping your business / domain objects directly forces you to design your business / domain objects around the data, and reuse becomes about data, not behavior. I like ORMs, if used correctly, because you have a strongly typed layer to access your data which can easily be code genned. You can then really quickly find out that some column has disappeared by compiling. –  Andy Apr 13 at 21:57
    
@Andy If you do it like that, then you are using ORM wrong. You should design your mappings based on the domain, not other way around. –  Euphoric Jul 14 at 5:37

1 Answer 1

This is what we use the Hibernate Query Language (hql) for - to select only the desired data when the entire object web is not needed. For example:

select new map (s.code as sCode, s.name as sName, i.code as iCode, i.qty as qty, i.name as iName, i.stock as stock)
from TOrderFiscal tof 
join tof.suplier s
join tof.items i
join i.product p
where p.id = 12345;

You will get back a list of map of string to object, where each item in the list is a row in the result set represented as a map of the selected field aliases to the field values.

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