A sample linq query from MSDN:
var expensiveInStockProducts =
from p in products
where p.UnitsInStock > 0 && p.UnitPrice > 3.00M
select p;
Does this query select EVERY column from the database table immediately, or does it return some sort of pointer that retieves the actual column data on demand? ie. If there are 50 columns in my table and I only use a single p.UnitsInStock in my actual code, then am I retrieving 50 times more data than I expected?
if you debugged that then you would probably see every column in your products table in the SELECT ... portion of the query
if you did select p.UnitsInStock you would only see that in the SELECT ... portion of the query.
So to answer your question, yes, it does select every column unless you specify what you want or dump the selection into an anonymous object like so:
var expensiveInStockProducts =
from p in products
where p.UnitsInStock > 0 && p.UnitPrice > 3.00M
select new { p.UnitsInStock, p.SomeOtherColumn }
I would advise using LINQPad if you want to see the generated SQL it really helps to visualise, just to help with what you want you can (if you only need the data locally) use an anonymous object or select into a concrete class within your applications model,
so
Anonymous
var expensiveInStockProducts =
from p in products
where p.UnitsInStock > 0 && p.UnitPrice > 3.00M
select new {
p.ColumnIWant1,
p.ColumnIWant2
};
or for a concrete class
var expensiveInStockProducts =
from p in products
where p.UnitsInStock > 0 && p.UnitPrice > 3.00M
select new MyClass() {
ColumnIWantAsField1 = p.ColumnIWant1,
ColumnIWantAsField2 = p.ColumnIWant2
};
