T>Destination.i.str2 = Source.i.str2;
T>

static long EmitMapper_Simple(int mappingsCount)
{
    var s = new B2();
    var d = new A2();

    var sw = new Stopwatch();
    sw.Start();

    for (int i = 0; i < mappingsCount; ++i)
    {
        var mapper = ObjectsMapperManager.DefaultInstance.GetMapper<B2, A2>(
            new DefaultMapConfig().NullSubstitution<decimal?,int>( state => 42 ));
        d = mapper.Map(s);
    }

    sw.Stop();
    return sw.ElapsedMilliseconds;
}

2) Очень гибкая. Проецировать можно что угодно на что угодно. Например, датаридер на объекты, объекты на SQL команды (UPDATE, INSERT), объекты на строку (сериализация), строку на объекты (десериализация) и так далее.

IT>>    public decimal? n5 = null;
IT>>

CREATE TABLE MyTable
(
    Field1 int NOT NULL PRIMARY KEY,
    Field2 int NOT NULL
)

SELECT Field1, Field2
FROM MyTable WHERE ...
UNION ALL
SELECT NULL, Field2
FROM MyTable WHERE ...

T>var mapper = ObjectsMapperManager.DefaultInstance.GetMapper<B2, A2>(
T>        new DefaultMapConfig().NullSubstitution<decimal?,int>( state => 42 )
T>    );
T>

IT>>...
IT>>

cmd.CommandText = "SELECT * FROM Customers";        // Test1
cmd.CommandText = "SELECT Phone, * FROM Customers"; // Test2

T>Во-первых, EM — это не про базы данных. Конфигурация мэппера для дадатидера была показана для примера. Во-вторых, отставание было на считанные проценты на синтетическом примере, при котором вызов "SqlCommand.ExecuteReader" по результатам профилирования составляет всего 4% от общего времени работы программы. В-третьих это уже поправлено

IT>>public DTOCustomer GetCustomer(Guid customerId)
IT>>{
IT>>    using (var dc = new DataContext())
IT>>    {
IT>>        var customer = dc.Customers.Where(c => c.CustomerID == customerId).Single();
IT>>        return ObjectsMapperManager.DefaultInstance.GetMapper<Customer, DTOCustomer>().Map(customer);
IT>>    }
IT>>}
IT>>

Map.Object2Object<Customer,DTOCustomer>(customer);

или даже

Map.To<DTOCustomer>.From(customer);

INSERT INTO (...)
SELECT ... FROM ...

H>P.S. Перехожу на BL, хотя надо ознакомиться с лицензией

var p = DbContext.Person.Where(_ => _.Id = myIdToDelete);
DbContext.DeleteOnSubmit(p);
DbContext.SubmitChanges();

public class Program
{
    public static IMappingConfigurator config1;
    public static IMappingConfigurator config2;

    static Program()
    {
        config1 = new DefaultMapConfig()
            .MatchMembers((m1, m2) => m1.ToLower() == m2.ToLower()) // ignore case of field names
            .NullSubstitution<object, int>(state => 42) // all nulls will be int 42
            .SetConfigName("config1");

        config2 = new DefaultMapConfig()
            .NullSubstitution<object, object>(state => DBNull.Value) // all nulls will be DBNull.Value
            .SetConfigName("config2");
    }
...
    public void Foo()
    {
        ...
        var dest = ObjectsMapperManager.DefaultInstance.GetMapper<Source, Destination>(config1).Map(source);
    }
...
}

DefaultMapConfig.Instance.MatchMembers((m1, m2) => m1.ToLower() == m2.ToLower());
...
dest = ObjectsMapperManager.DefaultInstance.GetMapper<Source, Destination>().Map(source);

Essential point of the source code above is not that it is another one "Super ORM". Essential point is that you can yourself develop very effective and light database access utilities in respect to your project requirements. Sometimes it is more preferable than using some huge generic ORM.

T>>var mapper = ObjectsMapperManager.DefaultInstance.GetMapper<B2, A2>(
T>>        new DefaultMapConfig().NullSubstitution<decimal?,int>( state => 42 )
T>>    );
T>>

IT>cmd.CommandText = "SELECT * FROM Customers";        // Test1
IT>cmd.CommandText = "SELECT Phone, * FROM Customers"; // Test2
IT>

LINQ tests:
  Testing: BLToolkit (BLT)
  Testing: ADO.NET Entity Framework (EF)
  Testing: DataObjects.Net (DO)
  Testing: LightSpeed (LS)
  Testing: LINQ to SQL (L2S)
  Testing: NHibernate (NH)
  Testing: OpenAccess (OA)

LINQ tests scorecard:
                                       BLT        EF        DO        LS       L2S        NH        OA   Maximum      Unit
LINQ Implementation:            
  Aggregates                             3         0         0         3         0         3         2         5       f/a
  All/Any/Contains                       5         3         0         6         1       4/2         4         6       f/a
  Complex                                6         1         0         6         0         6         5         6       f/a
  Element operations                     5         4         0         6         2         6         5         9       f/a
  Filtering                              0       4/2         0       5/5       2/2       6/1         2        12       f/a
  Grouping                               2         1         0        10         1      10/2         5        10       f/a
  Join                                   2         1         0         4         0         4         2         4       f/a
  Ordering                               0       2/1         0       5/1         2         6         3         8       f/a
  Projections                          3/1       3/1       3/3       9/2       2/1       6/1         3        13       f/a
  References                             1         0         0         4         0         3         1         4       f/a
  Set operations                         0         0         0       5/1         0       6/2       4/1         9       f/a
  Standard functions                     0        12         2        12       3/1        20       9/1        25       f/a
  Take/Skip                              1         1         0       2/1         0       2/1         2         5       f/a
  Type casts                             0         1         0       3/1         1         4         2         5       f/a
Total:                          
  Performed                            121       121       121       121       121       121       121       121         #
  Passed                                93        88       116        41       107        35        72       121         #
  Failed                                28        33         5        80        14        86        49       121         #
    Properly                            27        29         2        69        10        77        47       121         #
    Asserted                             1         4         3        11         4         9         2       121         #
  Score                               76.9      72.7      95.9      33.9      88.4      28.9      59.5     100.0         %

Units:
  f/a: total count of failed tests [ / count of tests failed with assertion ],
       less is better (0 is ideal);
  #:   count;
  %:   percentage (% of passed tests), more is better.

var mapper = ObjectsMapperManager.DefaultInstance.GetMapper<Source, Destination>(
        new DefaultMapConfig().ConstructBy<Foo>( () => new FooDescendant("hello!") )
    );

T>>Ой

CREATE TABLE [dbo].[test](
    [col1] [int] NOT NULL,
    [col2] [int] NOT NULL,
    [col3] [int] NOT NULL,
    [col4] [int] NOT NULL,
    [col5] [int] NOT NULL,
    [col6] [int] NOT NULL
)
GO

DECLARE @i INT
SET @i = 0
while (@i < 100)
BEGIN
    INSERT INTO test 
    VALUES
    (
        RAND() * 100, RAND() * 100, RAND() * 100, RAND() * 100, RAND() * 100,  RAND() * 100
    )
    SET @i = @i + 1
END
GO

public class test
{
    public int col1;
    public int col2;
    public int col3;
    public int col4;
    public int col5;
    public int col6;
}