.NET Core，使用 XMLParser 对特定实体的循环引用

问题描述

我正在使用 C# .Net Core 和 XMLSerializer，我已经检查了各种其他问题，但提供的答案似乎都不适合我。我有一个有多个时间块的 MaintenanceMoment，所以是一对多的关系，我像下面这样创建它：

我的型号代码：

PRMaintenanceMoment.cs

    public class PRMaintenanceMoment
    {
      [XmlIgnore]
      public int ID { get; set; }

      [required]
      [displayFormat(ApplyFormatInEditMode = true,DataFormatString = "{0:yyyy-MM-dd}")]
      public string EarliestExecutionDate { get; set; }

      [required]
      [displayFormat(ApplyFormatInEditMode = true,DataFormatString = "{0:yyyy-MM-dd}")]
      public string LatestExecutionDate { get; set; }

      public List<Timeblock> Timeblock { get; set; } = new List<Timeblock>();
    }

Timeblock.cs

public class Timeblock
{
    [XmlIgnore]
    public int ID { get; set; }

    [ForeignKey("MaintenanceMomentID")]
    public PRMaintenanceMoment MaintenanceMoment { get; set; }

    [required]
    [displayFormat(ApplyFormatInEditMode = true,DataFormatString = "{0:hh:mm:ss}")]
    public DateTime EarliestExecutionTime { get; set; }

    [required]
    [displayFormat(ApplyFormatInEditMode = true,DataFormatString = "{0:hh:mm:ss}")]
    public DateTime LatestExecutionTime { get; set; }
}

我的数据库上下文中的引用是这样制作的： ApplicationDbContext.cs

public class ApplicationDbContext : DbContext
{
    public ApplicationDbContext(DbContextOptions<ApplicationDbContext> options)
        : base(options) { }

    public DbSet<Timeblock> Timeblocks { get; set; }

 protected override void OnModelCreating(ModelBuilder modelBuilder)
 {
        modelBuilder.Entity<PRMaintenanceMoment>()
            .HasMany(tb => tb.Timeblock)
            .WithOne(pr => pr.MaintenanceMoment);
 }
}

为 MaintenanceMoment 提供服务的我的控制器是这样创建的（我已经排除了通用存储库和接口，因为它们对本示例无关紧要）：

PRMaintenanceMoment.cs

    public class PRMaintenanceMomentRepository : GenericRepository<PRMaintenanceMoment>,IPRMaintenanceMomentRepository
{
    public PRMaintenanceMomentRepository(ApplicationDbContext context)
        : base(context) { }

    public override List<PRMaintenanceMoment> Index()
    {
        var context = _context.PRMaintenanceMoments
               .Include(PRMaintenanceMoment => PRMaintenanceMoment.Timeblock)
            .ToList();

        return context;
    }

    public void Update(int id,PRMaintenanceMoment maintenanceMoment)
    {
        PRMaintenanceMoment DBPRMaintenanceMoment = _context.PRMaintenanceMoments.FirstOrDefault(ms => ms.ID.Equals(id));

        _context.Entry<PRMaintenanceMoment>(DBPRMaintenanceMoment).CurrentValues.SetValues(maintenanceMoment);

        _context.SaveChanges();
    }
}

最终创建的迁移显示如下：

migrationBuilder.CreateTable(
            name: "PRMaintenanceMoments",columns: table => new
            {
                ID = table.Column<int>(nullable: false)
                    .Annotation("MysqL:ValueGenerationStrategy",MysqLValueGenerationStrategy.IdentityColumn),EarliestExecutionDate = table.Column<string>(nullable: false),LatestExecutionDate = table.Column<string>(nullable: false)
            },constraints: table =>
            {
                table.PrimaryKey("PK_PRMaintenanceMoments",x => x.ID);
            });

        migrationBuilder.CreateTable(
            name: "Timeblocks",MaintenanceMomentID = table.Column<int>(nullable: true),EarliestExecutionTime = table.Column<DateTime>(nullable: false),LatestExecutionTime = table.Column<DateTime>(nullable: false)
            },constraints: table =>
            {
                table.PrimaryKey("PK_Timeblocks",x => x.ID);
                table.ForeignKey(
                    name: "FK_Timeblocks_PRMaintenanceMoments_MaintenanceMomentID",column: x => x.MaintenanceMomentID,principalTable: "PRMaintenanceMoments",principalColumn: "ID",onDelete: referentialAction.Restrict);
            });

        migrationBuilder.CreateIndex(
            name: "IX_PlanningRequests_PRMaintenanceMomentID",table: "PlanningRequests",column: "PRMaintenanceMomentID");

        migrationBuilder.CreateIndex(
            name: "IX_Timeblocks_MaintenanceMomentID",table: "Timeblocks",column: "MaintenanceMomentID");

这对我来说似乎没什么问题，正如许多问题所暗示的那样，从 JSON 序列化程序中添加 ReferenceLoopHandling。我试过这个，但这似乎没有帮助。为了完成起见，我添加了我的 startup.cs 文件中最重要的部分；这当然不是完整文件，而是最重要的设置。

startup.cs

    public void ConfigureServices(IServiceCollection services)
    {
        services.AddControllers()
             .AddXmlSerializerFormatters(); // Adding the XML serializer here

        services.AddMvc(options =>
        {
            options.MaxValidationDepth = 64;
            options.InputFormatters.Add(new XmlSerializerInputFormatter(options));
            options.OutputFormatters.Add(new XmlDataContractSerializerOutputFormatter());
        });

services.AddMvc().AddNewtonsoftJson(jsonoptions => { jsonoptions.SerializerSettings.ReferenceLoopHandling = ReferenceLoopHandling.Ignore;  });

Encoding.RegisterProvider(CodePagesEncodingProvider.Instance);
}

    public void Configure(IApplicationBuilder app,IWebHostEnvironment env)
    {
        app.UseRouting();
        app.UseAuthentication();
        app.UseAuthorization();

        app.UseEndpoints(endpoints =>
        {
            endpoints.MapControllers();
        });
    }

最后抛出的确切错误是：

system.invalidOperationException: There was an error generating the XML document.
---> system.invalidOperationException: A circular reference was detected while serializing an object of type SALES005.Models.PRMaintenanceMoment.
at System.Xml.Serialization.XmlSerializationWriter.WriteStartElement(String name,String ns,Object o,Boolean writePrefixed,XmlSerializerNamespaces xmlns)
at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterList1.Write3_PRMaintenanceMoment(String n,PRMaintenanceMoment o,Boolean isNullable,Boolean needType)
at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterList1.Write2_Timeblock(String n,Timeblock o,Boolean needType)
at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterList1.Write3_PRMaintenanceMoment(String n,Boolean needType)
at Microsoft.Xml.Serialization.GeneratedAssembly.XmlSerializationWriterList1.Write4_ArrayOfPRMaintenanceMoment(Object o)

解决方法

Newtonsoft 可以解决json循环引用，但是不能解决xml。所以你可以改变查询方法。

public List<PRMaintenanceMoment> get6()
    {
        var pRMaintenanceMoments = (from prm in _db.PRMaintenanceMoment
                     
                   select new PRMaintenanceMoment
                   {
                       ID=prm.ID,EarliestExecutionDate=prm.EarliestExecutionDate,LatestExecutionDate=prm.LatestExecutionDate,Timeblock=prm.Timeblock.Select(c=>new Timeblock
                         {
                              ID=c.ID,}).ToList()
                          
                   }).ToList();
        return pRMaintenanceMoments;
    }