使用AutoFixture生成一对多数据时如何绑定Book的AuthorId属性

AutoFixture 默认不会自动处理实体间的外键关联，你可以通过自定义生成规则实现绑定，以下是两种常用方案：

方案1：临时自定义构造规则（适合单次使用场景） #

无需额外定义扩展类，直接在构造fixture时指定关联逻辑即可：

using AutoFixture;

var fixture = new Fixture();

// 关闭默认循环引用检测，避免Author和Book的关联触发递归异常
fixture.Behaviors.OfType<ThrowingRecursionBehavior>()
    .ToList()
    .ForEach(b => fixture.Behaviors.Remove(b));
fixture.Behaviors.Add(new OmitOnRecursionBehavior());

// 自定义Author生成规则，绑定Book的AuthorId
fixture.Customize<Author>(c => c
    .Do(author =>
    {
        // 生成3个关联的Book，可自行调整数量
        var relatedBooks = fixture.CreateMany<Book>(3).ToList();
        relatedBooks.ForEach(book => book.AuthorId = author.Id);
        author.Books = relatedBooks;
    })
);

// 直接生成Author列表，所有关联Book的AuthorId已自动匹配对应Author的Id
var authorList = fixture.CreateMany<Author>(10).ToList();

方案2：全局自定义生成器（适合多处复用场景） #

如果项目中多处需要生成带关联Book的Author，可以实现自定义ISpecimenBuilder统一处理：

using AutoFixture;
using AutoFixture.Kernel;

public class AuthorWithBooksBuilder : ISpecimenBuilder
{
    private readonly int _bookCountPerAuthor;

    public AuthorWithBooksBuilder(int bookCountPerAuthor = 3)
    {
        _bookCountPerAuthor = bookCountPerAuthor;
    }

    public object Create(object request, ISpecimenContext context)
    {
        if (request is not Type type || type != typeof(Author))
        {
            return new NoSpecimen();
        }

        // 生成基础Author属性
        var author = new Author
        {
            Id = (int)context.Resolve(typeof(int)),
            AuthorName = (string)context.Resolve(typeof(string))
        };

        // 生成关联Book并绑定外键
        var books = ((IEnumerable<Book>)context.Resolve(typeof(IEnumerable<Book>)))
            .Take(_bookCountPerAuthor)
            .ToList();
        books.ForEach(book => book.AuthorId = author.Id);
        author.Books = books;

        return author;
    }
}

使用方式：

var fixture = new Fixture();
// 关闭递归检测逻辑和方案1一致
fixture.Behaviors.OfType<ThrowingRecursionBehavior>()
    .ToList()
    .ForEach(b => fixture.Behaviors.Remove(b));
fixture.Behaviors.Add(new OmitOnRecursionBehavior());

// 注册全局生成器，可指定每个Author关联的Book数量
fixture.Customizations.Add(new AuthorWithBooksBuilder(bookCountPerAuthor: 2));

// 生成Author列表
var authorList = fixture.CreateMany<Author>(10).ToList();

内容的提问来源于stack exchange，提问作者Emily