IEnumerable extension method that ingests SqlCommand and returns query results
You are never using b in the method. Why make it an extension method if you are going to completely ignore the first argument? In order to use this code, you need to create a new instance that is immediately thrown away. That is unneeded waste.

Instead, you can just specify the generic type in the function call.

public static IEnumerable&lt;T&gt; FromCommand&lt;T&gt;(SqlCommand command)
{
    // ...
}

[Description("Selects and returns all rows.")]
public static IEnumerable&lt;MyType&gt; SelectAll()
{
    SqlCommand command = new SqlCommand(QueryRepository.SELECT_MyType_ALL, Conn.ConnectionString) { CommandTimeout = 0 };

    return FromCommand&lt;MyType&gt;(command);
}




The expression that assigns to properties is over 100 characters. That doesn't count the indentation or the variable declaration. That is going to be hard to follow. I suggest that you extract the lambda being passed to Where() into a static function with a descriptive name. That way I don't need to think about what is being filtered out.



You are adding extra blank lines after opening curly brackets and before some closing curly brackets. This is just inflating the file size and not helping readability.