Entity framework transferred data in bytes

Question

I'm using EF6

this is my class

public partial class tbl_Persons
    {
        public int ID { get; set; }
        public string Name { get; set; }
        public byte Age { get; set; }
    }

How much (bytes) will be transferred from the server to the client when used this code ?

using (var db = new testEntities())
{
    var q = db.tbl_Persons.FirstOrDefault(a => a.ID == 1234).Age;
}

Just transferred {(Age)(1 byte)} or transferred all properties {(ID + Name + Age)(10 bytes)} then select Age on client ?

How can I transfer only (Age)(1 byte) ? (I need to transfer minimum data from server)

Answer 1

The expression

var q = db.tbl_Persons.FirstOrDefault(a => a.ID == 1234).Age;

is equivalent of

var person = db.tbl_Persons.FirstOrDefault(a => a.ID == 1234);
var age = person.Age;

So you first retrieve and materialize a whole object (with all properties) from the database, and then take a single property (byte in your case) from the result.

In order to fetch just the property in question, you should use a not so concise, but more efficient Where + Select + FirstOrDefault (no predicate version):

var age = db.tbl_Persons.Where(p => p.ID == 1234).Select(p => p.Age).FirstOrDefault();

or with query syntax

var age = (from p in db.tbl_Persons where p.ID == 1234 select p.Age).FirstOrDefault();