C# – Communication between BLL and DAL

bllcdata-access-layernetvb.net

Solution setup:

DAL (class library)
BLL (class library)
Common (class library (some common functionality – enums, logging, exceptions,…))
Application1 (Windows Application)
Application2 (Windows Application)
WebApp (Web application)
…

Let's say I have a Customer entity, which is:

a table in SQL server
a CustomerDataTable in DAL
a Customer class in BLL
a BLL.Customer class in all the applications

What kind of objects should BLL and DAL use for communication – DataTable or List<Customer> (for example)? In first case, BLL logic should transform Customer object to DataTable and send it to DAL. In secod case, DAL layer should be aware of Customer class, which is in BLL layer. But originaly DLL references DAL and not opposite…

Should I put all classes into seperate assembly, which is referenced by all others (Common, BusinessObjects, …)? In this case I could use Customer class in all my projects.

Should I even bother to seperate DAL and BLL when I know, that only one BLL will use my DAL. In this case I could merge them together into one project.

PS – I am reading about DataTables and a lot of people say that we shouldn't use them at all. What are better options? Maybe it is time for me to learn some ORM mapping tools 🙂

Best Answer

In my opinion you should have another Layer (seperate dll). Like "domain", where would you keep all entities like Customer. Then simply include in all higher levels(DAL, BLL, UI and others) in hierarchy this assembly.

Sample architecture can look like this:

(Database) <-> DAL <-> BL <-> UI

and on all levels you will have access to "domain" layer. DAL should return List not a DataTable. On some stage your development process you may want to use in DAL some OMR like NHibernate with would also return a List, probably.

This is the style that Microsoft tends to use in their examples.

It appears that the guidance in this area may have changed, as StyleCop now enforces the use of the C# specific aliases.

C# – the difference between const and readonly in C#

Apart from the apparent difference of

having to declare the value at the time of a definition for a const VS readonly values can be computed dynamically but need to be assigned before the constructor exits.. after that it is frozen.
const's are implicitly static. You use a ClassName.ConstantName notation to access them.

There is a subtle difference. Consider a class defined in AssemblyA.

public class Const_V_Readonly
{
  public const int I_CONST_VALUE = 2;
  public readonly int I_RO_VALUE;
  public Const_V_Readonly()
  {
     I_RO_VALUE = 3;
  }
}

AssemblyB references AssemblyA and uses these values in code. When this is compiled:

in the case of the const value, it is like a find-replace. The value 2 is 'baked into' the AssemblyB's IL. This means that if tomorrow I update I_CONST_VALUE to 20, AssemblyB would still have 2 till I recompile it.
in the case of the readonly value, it is like a ref to a memory location. The value is not baked into AssemblyB's IL. This means that if the memory location is updated, AssemblyB gets the new value without recompilation. So if I_RO_VALUE is updated to 30, you only need to build AssemblyA and all clients do not need to be recompiled.

So if you are confident that the value of the constant won't change, use a const.

public const int CM_IN_A_METER = 100;

But if you have a constant that may change (e.g. w.r.t. precision).. or when in doubt, use a readonly.

public readonly float PI = 3.14;

Update: Aku needs to get a mention because he pointed this out first. Also I need to plug where I learned this: Effective C# - Bill Wagner

Best Answer

Related Solutions

C# – the difference between String and string in C#

This is the style that Microsoft tends to use in their examples.

C# – the difference between const and readonly in C#

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