Why is ORM considered good but “select *” considered bad?

Question

Doesn\'t an ORM usually involve doing something like a select *?

If I have a table, MyThing, with column A, B, C, D, etc, then there typically would be an object, MyThin

Answer 1

Linq to Sql, or any implementation of IQueryable, uses a syntax which ultimately puts you in control of the selected data. The definition of a query is also the definition of its result set.

This neatly avoids the select * issue by removing data shape responsibilities from the ORM.

For example, to select all columns:

from c in data.Customers
select c

To select a subset:

from c in data.Customers
select new
{
  c.FirstName,
  c.LastName,
  c.Email
}

To select a combination:

from c in data.Customers
join o in data.Orders on c.CustomerId equals o.CustomerId
select new
{
  Name = c.FirstName + " " + c.LastName,
  Email = c.Email,
  Date = o.DateSubmitted
}