Builder pattern with nested objects

问题:

Hi I'm stuck with a problem.

I want to implement the builder pattern to make creating my objects easier. The problem I face has to do with nested object. The object I would like to create has a list of other objects in it, and I don't really have an idea on how to tackle it.

I want to be able to do the following (Simpler objects for example):

Receipt RestaurantReceipt = new ReceiptBuilder()
.withDate("value")
.withName("value")
.AddItem("value")
    .WithIngredients("value")
    .WithType("value")
.AddItem("value")
    .WithIngredients("value")
    .WithType("value")
.build();

Or something like:

Receipt RestaurantReceipt = new ReceiptBuilder()
.withDate("value")
.withName("value")
.AddItem("value", item => {
  .WithIngredients("value")
  .WithType("value")
})
.AddItem("value", item => {
  .WithIngredients("value")
  .WithType("value")
})
.build();

Example should be representative for my situation, although if got more than one type of nested object.

回答1:

Given code like this

var rb = new ReceiptBuilder();
var receipt = rb.WithName("Name")
            .WithDate(DateTime.Now)
            .WithItem("Item1", i => i.WithIngredients("Ingredients1"))
            .WithItem("Item2", i => i.WithIngredients("Ingredients1"))
            .Build();
Console.WriteLine(receipt);

Your builder is pretty simple, making use of some simple predicates inside the AddItem builder method to allow the consumer to configure each item in a similar "builder" pattern to the top level ReceiptBuilder:

public class ReceiptBuilder
{
    private Receipt r;

    public ReceiptBuilder()
    {
        r = new Receipt();
    }

    public ReceiptBuilder WithName(string name)
    {
        r.Name = name;
        return this;
    }

    public ReceiptBuilder WithDate(DateTime dt)
    {
        r.Date = dt;
        return this;
    }

    public ReceiptBuilder WithItem(string text, Action<ReceiptItemBuilder> itemBuilder)
    {
        var rib = new ReceiptItemBuilder(text);
        itemBuilder(rib);
        r.AddItem(rib.Build());
        return this;
    }

    public Receipt Build()
    {
        return r;
    }
}

public class ReceiptItemBuilder
{
    private ReceiptItem ri;

    public ReceiptItemBuilder(string text)
    {
        ri = new ReceiptItem(text);
    }

    public ReceiptItemBuilder WithIngredients(string ings)
    {
        ri.Ingredients = ings;
        return this;
    }

    // WithType omitted for brevity. 

    internal ReceiptItem Build()
    {
        return ri;
    }
}

Working example: http://rextester.com/IRR50897