Constructor Design - Loading Data inside the constructor (C#)

问题

I have the "feeling" that my design to invoke a method to load data inside the constructor is not right.

I try to write a class that provides the basic logic to perform a calculation (discount, tax, total-amount etc.) for invoices-, orders- or quotes-record. In most cases are the same set of attributes needed (e.g. the attribute "quantity" is present in all entities/tables).

In my current design is use this base class (note this is not the real code, i am at home and do not have access to the code-base, so typos are likely):

public abstract class HeadCalculationEngineBase
{
    protected readonly IOrganisationService orgService;
    protected decimal pricePerUnit;
    protected decimal quantity;

    public HeadCalculationEngineBae(Guid entityid, IOrganisationService service)
    {
        this.orgService = service;
        this.populate(this.loadEntityData(id));
    }

    public virtual Entity loadEntityData(Guid id)
    {
        var columns = new ColumnSet("pricePerUnit", "quantity");

        return this.orgService.Retrieve(id, columns);
    }

    protected virtual populate(Entity data)
    {
        this.pricePerUnit = data["pricePerUnit"];
        this.quantity = data["quantity"];
    }
}

This design gives me the option to override the virtual member and load additional attributes for my implementation for the invoice entity:

public class HeadCalculationInvoiceEngine : HeadCalculationEngineBase
{
    protected decimal discount;

    public HeadCalculationInvoiceEngine(Guid entityid, IOrganisationService service)
        :base(entityid, service)
    { }

    public override Entity loadEntityData(Guid id)
    {
        var columns = new ColumnSet("pricePerUnit", "quantity", "discount");

        return this.orgService.Retrieve(id, columns);
    }

    protected override populate(Entity data)
    {
        this.pricePerUnit = data["pricePerUnit"];
        this.quantity = data["quantity"];
        this.discount = data["discount"];
    }
}

So my problem comes down to the question: Should I load data inside the constructor?

回答1:

Better to keep constructors lightweight and avoid long and especially remote calls.

Failures in constructor are harder to reason about than exceptions thrown by methods.
it is harder to mock such functionality for unit test (you can't extract constructor to interface for example)
constructors can't be asynchronous - so when you try to switch to modern asynchronous APIs to access remote resources you'll have to significantly modify way you construct objects.

来源：https://stackoverflow.com/questions/32465908/constructor-design-loading-data-inside-the-constructor-c

标签

constructor