.net – the impact of lazy=”false” on class element of NHibernate mapping

lazy-loadingnetnhibernate

I'm working with a legacy system that I'm experimenting with adding NHibernate to. I have class that I need to be mapped to a table, but it has lots of existing methods that are not virtual.

I discovered that I can get NHibernate to load the mapping successfully even with the non-virtual methods present if I set the "lazy" attribute on the class element of the mapping file to "false". I'm wondering what impact this will have on my use of NHibernate with this class.

I understand the meaning of non-lazy loading on collections that belong to an object, but I'm not clear on the meaning of what lazy or eager loading on a class would be. Does that mean all collections belonging to that object would be eager-loaded? Or does it mean that NHibernate no longer uses a dynamic proxy in place of the actual class? Something else?

Also, what's the best course of action here? Is setting that lazy=false value inadvisable? Should I create an interface that the class implements, and then map that to the table? Or should I just bite the bullet and mark all the existing methods on the class virtual?

Thanks in advance for any and all advice!

Best Answer

I always specify lazy=false on the class level in NHIbernate, because I do not want that NHibernate forces me to declare that properties are to be virtual, if I do not want this in my class-model.

When you specify 'lazy' at the class mapping (default), NHibernate uses a 'Dynamic Proxy' class at runtime. This Dynamic Proxy is a class that inherits from your class. Then, as far as I understand, the instance of the class should be initialized lazily / on-demand. In some cases, this should be better for performance (at least, that's what's being told).

But, since I do not like that NHibernate tells me how my class should look like, I've always specified lazy=false for all my classes, and I haven't ran into trouble yet. :)

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

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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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