ASP.Net Core Web API - ICollection 未显示在 JSON 结果集中

Question

我正在尝试执行 3 个过程以构建客户对象并将其返回给客户端。但是，在我的 api（服务器端）中，我可以正确看到结果。但是，不幸的是，结果集中（客户端）中缺少 ICollection 数据

我正在使用 Entity Framework 和 OData

所以，这是我的模型：

  public class Customer
    {
        [Key]
        public Guid Id { get; set; }
        public string Code { get; set; }
        public string Name { get; set; }
        public string VatCode { get; set; }
        public string ChamberOfCommerceCode { get; set; }
        public DateTime Modified { get; set; }
        public DateTime Created { get; set; }
        public string LanguageCode { get; set; }
        public decimal Discount { get; set; }
        public string CustomerManager { get; set; }
        public Guid PriceList { get; set; }
        public Guid PaymentCondition { get; set; }
       // public bool VatLiable { get; set; }
        public bool IsBlocked { get; set; }
        public bool IsProspect { get; set; }
        public bool IsSuspect { get; set; }
        public string Website { get; set; }
        public string DashboardUrl { get; set; }
        public string Email { get; set; }
        public string Phone { get; set; }
        public string Fax { get; set; }
        public ICollection<FreeFields> FreeFields { get; set; }
  //      [NotMapped]
      //  public Dictionary<string, string> UknownElements { get; set; }
        [ForeignKey(nameof(Contacts.Customer))]
        public ICollection<Contacts> Contact { get; set; }
        [ForeignKey(nameof(Addresses.Customer))]
        public ICollection<Addresses> Address { get; set; }
    }

如您所见，我们在其中有 2 个 ICollections：联系人和地址。 这里是这两个的模型：

联系人型号

public class Contacts
    {
        [Key]
        public Guid Id { get; set; }
        public string FirstName { get; set; }
        public string MiddleName { get; set; }
        public string LastName { get; set; }
        public string Initials { get; set; }
        public string Function { get; set; }
        [Column("Customer")]
        public Guid Customer { get; set; }
        public string Email { get; set; }
        public string Phone { get; set; }
        public string Mobile { get; set; }
        public string LanguageCode { get; set; }
        public bool IsMainContact { get; set; }
        public string Gender { get; set; }
        public string Username { get; set; }
    }

和地址

 public class Addresses
    {
        [Key]
        public Guid Id { get; set; }
        public string AddressLine1 { get; set; }
        public string AddressLine2 { get; set; }
        public string AddressLine3 { get; set; }
        public string PostalCode { get; set; }
        public string City { get; set; }
        public string Country { get; set; }
        public string CountryCode { get; set; }
        public string Type { get; set; }
        [Column("Customer")]
        public Guid Customer { get; set; }// This Property should be GUID instead of String..
        public bool IsMainAddress { get; set; }
        public string Route { get; set; }
        public string State { get; set; }
    }

现在，在我的控制器中，我从存储过程中获取数据并创建模型：

  public IList<Customer> GetAllCustomers()
        {
            //Initialize the objects
            IList<Customer> customers = null;
            ICollection<Contacts> contacts = null;
            ICollection<Addresses> addresses = null;
            Dictionary<string, string> thisdict = null;
            //Fetch the data from stored procedures
            customers = db.Customers.FromSql("SIP_API_MONDIA_Customers_sel").ToList();
            contacts = db.Contacts.FromSql("SIP_API_MONDIA_Contacts_sel").ToList();
            addresses = db.Addresses.FromSql("SIP_API_MONDIA_Address_sel").ToList();

            //Loop through customers and add the contact and addresses when required
            foreach(var item in customers)
            {
                item.Contact = contacts.Where(x => x.Customer == item.Id).ToList();
                item.Address = addresses.Where(x => x.Customer == item.Id).ToList();
             //   item.UknownElements = thisdict;

            }
            return customers;
        }

Tihs 工作得很好，我可以通过断点看到 Customers 对象已被填充。地址和联系方式也正确。但是，一旦我将它返回给客户端，结果就会丢失两个 ICollections..

我觉得我错过了一个小细节，但我找不到它。

Answer 1

首先，如果您遵循命名约定，则无需显式使用属性。 Key 属性可以安全地删除。 ForeignKey 属性可以在将属性名称更改为复数名称时删除：Contacts 和 Addresses。我强烈建议您对类使用单数名称，对集合导航属性使用复数名称（例如在一对多关系中）。

// Contact is name of class, plural name for property: Contacts
public ICollection<Contact> Contacts { get; set; }

如果您使用的是 OData，您应该构建您的 EDM model（您没有向我们展示）。如果您有权访问DbContext，也不要对简单的SELECT 使用存储过程。 您的整个控制器逻辑是不必要的，可以替换为：

[EnableQuery]
public IQueryable<Customer> GetAllCustomers()
{
    return db.Customers;
}

所以在代码中它可能看起来像：

客户类

public class Customer
{
    public Guid Id { get; set; }
    public string Code { get; set; }
    public string Name { get; set; }
    public string VatCode { get; set; }
    public string ChamberOfCommerceCode { get; set; }
    public DateTime Modified { get; set; }
    public DateTime Created { get; set; }
    public string LanguageCode { get; set; }
    public decimal Discount { get; set; }
    public string CustomerManager { get; set; }
    public Guid PriceList { get; set; }
    public Guid PaymentCondition { get; set; }
    public bool IsBlocked { get; set; }
    public bool IsProspect { get; set; }
    public bool IsSuspect { get; set; }
    public string Website { get; set; }
    public string DashboardUrl { get; set; }
    public string Email { get; set; }
    public string Phone { get; set; }
    public string Fax { get; set; }
    public ICollection<FreeFields> FreeFields { get; set; }

    public ICollection<Contact> Contacts { get; set; }
    public ICollection<Address> Addresses { get; set; }
}

联系班级

public class Contact
{
    public Guid Id { get; set; }
    public string FirstName { get; set; }
    public string MiddleName { get; set; }
    public string LastName { get; set; }
    public string Initials { get; set; }
    public string Function { get; set; }
    public Guid Customer { get; set; }
    public string Email { get; set; }
    public string Phone { get; set; }
    public string Mobile { get; set; }
    public string LanguageCode { get; set; }
    public bool IsMainContact { get; set; }
    public string Gender { get; set; }
    public string Username { get; set; }

    public Guid CustomerId { get; set; }
    // If you want to use class reference navigation property (also called as "hard reference").
    // That can be used in "$expand" or "$select" for example.
    // Uncomment the following line:
    // public Customer Customer { get; set }
}

地址类

public class Address
{
    public Guid Id { get; set; }
    public string AddressLine1 { get; set; }
    public string AddressLine2 { get; set; }
    public string AddressLine3 { get; set; }
    public string PostalCode { get; set; }
    public string City { get; set; }
    public string Country { get; set; }
    public string CountryCode { get; set; }
    public string Type { get; set; }
    public bool IsMainAddress { get; set; }
    public string Route { get; set; }
    public string State { get; set; }

    public Guid CustomerId { get; set; }
    // If you want to use class reference navigation property (also called as "hard reference").
    // That can be used in "$expand" or "$select" for example.
    // Uncomment the following line:
    // public Customer Customer { get; set }
}

构建您的 EDM 模型：

public class MyModelBuilder
{
    public IEdmModel GetEdmModel(IServiceProvider serviceProvider)
    {
        var builder = new ODataConventionModelBuilder(serviceProvider);

        builder.EntitySet<Address>("Addresses")
                        .EntityType
                        .Filter() // Allow for the $filter Command
                        .Count() // Allow for the $count Command
                        .Expand() // Allow for the $expand Command
                        .OrderBy() // Allow for the $orderby Command
                        .Page() // Allow for the $top and $skip Commands
                        .Select();// Allow for the $select Command; 

        builder.EntitySet<Contact>("Contacts")
                        .EntityType
                        .Filter() // Allow for the $filter Command
                        .Count() // Allow for the $count Command
                        .Expand() // Allow for the $expand Command
                        .OrderBy() // Allow for the $orderby Command
                        .Page() // Allow for the $top and $skip Commands
                        .Select() // Allow for the $select Command
                        .Expand(); 

        builder.EntitySet<Customer>("Customers")
                        .EntityType
                        .Filter() // Allow for the $filter Command
                        .Count() // Allow for the $count Command
                        .Expand() // Allow for the $expand Command
                        .OrderBy() // Allow for the $orderby Command
                        .Page() // Allow for the $top and $skip Commands
                        .Select() // Allow for the $select Command
                        .Expand(); 

        return builder.GetEdmModel();
    }
}

在启动中使用它：

public void ConfigureServices(IServiceCollection services)
{
    // ... Other Configurations 

    services.AddOData();
    services.AddTransient<MyModelBuilder>();

    // ... MVC Service Configurations 
}

public void Configure(IApplicationBuilder app, IHostingEnvironment env, MyModelBuilder modelBuilder)
{
    // ... Other Configurations

    app.UseMvc(routeBuilder =>
    {
        routeBuilder.MapODataServiceRoute("ODataRoutes", "odata", modelBuilder.GetEdmModel(app.ApplicationServices));
    });
}

最后创建控制器：

[Produces("application/json")]
public class CustomersController : ODataController
{
    private readonly MyDbContext _context;

    public CustomersController (MyDbContext context) => _context = context;

    [EnableQuery]
    public IQueryable<Customer> GetAllCustomers() => _context.Customers;
}

（在上面的代码中，我假设你已经正确配置了你的DbContext）

现在您应该可以使用$expand 或$select 来获取例如客户的所有地址。

HTTP GET /odata/Customers?$expand=Addresses

Answer 2

Odata 不支持在不使用扩展的情况下预先加载导航属性。但是您可以通过使用拦截器和更改 url 来强制将扩展包含在查询中。下面是实现：

using System;
using System.Web.Http.Controllers;
using System.Web.Http.OData;

namespace ODataWebAPI.API
{
    public class EnableQueryForExpand : EnableQueryAttribute
    {
       public override void OnActionExecuting(HttpActionContext actionContext)
       {
           var url = actionContext.Request.RequestUri.OriginalString;
           var newUrl = ModifyUrl(url);
           actionContext.Request.RequestUri = new Uri(newUrl);
           base.OnActionExecuting(actionContext);
       }

       private string ModifyUrl(string url)
       {
           if (!url.Contains("expand"))
           {
               if (url.Contains("?$"))
               {
                   url = url + "&$";
               }
               else
               {
                   url = url + "?$";
               }
               url = url + "expand=Category,Supplier";
           }
           return url;
       }
   }
}

并且你在控制器方法中使用了这个属性：

 [EnableQueryForExpand]
 public IQueryable<Customer> GetAllCustomers()
 {

 }

Answer 3

我相信您的问题归结为以下几行：

[ForeignKey(nameof(Contacts.Customer))]
public ICollection<Contacts> Contact { get; set; }
[ForeignKey(nameof(Addresses.Customer))]
public ICollection<Addresses> Address { get; set; }

ForeignKey 仅应用于实际的外键属性或该外键的导航属性：

[ForeignKey(nameof(Customer))]
public Guid CustomerId { get; set; }

public Customer Customer { get; set; }

或者

public Guid CustomerId { get; set; }

[ForeignKey(nameof(CustomerId)]
public Customer Customer { get; set; }

对于集合属性，需要使用InverseProperty：

[InverseProperty(nameof(Contacts.Customer))]
public ICollection<Contacts> Contact { get; set; }

总之，我认为 EF 没有正确创建关系，因为您在此处的错误，因此您得到空的联系人和地址列表，因为实际上没有相关的联系人或地址。

FWIW，这里使用存储过程非常效率低下，坦率地说是不必要的。执行简单 SELECT 的存储过程并不比仅发出 SELECT 更有效（如果不涉及多个表等，则没有优化的执行策略）。事实上，这样做，您正在查询所有联系人和所有地址，即使它们中只有一些或什至没有与您正在使用的客户相关。这可能是您通过网络无用传输的 吨 数据。