具有一对多关系的Azure GET操作

Question

我必须在Azure SQL数据库中具有一对多关系的表。

--Countries 
create table Countries 
(
    ID int not null primary key clustered identity, 
    Name varchar(100) not null 
) 
--Cities 
create table Cities 
(
    ID int not null primary key clustered identity, 
    Name varchar(100) not null, 
    CountryID int not null foreign key references Countries(ID) on delete cascade 
) 

我已经使用实体框架数据库第一个模型创建了Web API。生成的类看起来如下：

Country.cs

[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")] 
    public Country() 
    { 
     this.Cities = new HashSet<City>(); 
    } 

    public int ID { get; set; } 
    public string Name { get; set; } 
    [System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2227:CollectionPropertiesShouldBeReadOnly")] 
    public virtual ICollection<City> Cities { get; set; } 

City.cs

[System.Diagnostics.CodeAnalysis.SuppressMessage("Microsoft.Usage", "CA2214:DoNotCallOverridableMethodsInConstructors")] 
    public City() 
    { 

    } 

    public int ID { get; set; } 
    public string Name { get; set; } 
    public int CountryID { get; set; }  
    public virtual Country Country { get; set; } 

CitiesController.cs

private TripperDBEntities db = new TripperDBEntities(); 

    // GET: api/Cities 
    public IQueryable<City> GetCities() 
    { 
     return db.Cities; 
     } 

// POST: api/Countries 
     [ResponseType(typeof(Country))] 
     public async Task<IHttpActionResult> PostCountry(Country country) 
     { 
      if (!ModelState.IsValid) 
      { 
       return BadRequest(ModelState); 
      } 

      db.Countries.Add(country); 
      await db.SaveChangesAsync(); 

      return CreatedAtRoute("DefaultApi", new { id = country.ID }, country); 
     } 

调用get国家或GET城市返回

500内部服务器错误

Answer 1

如果加载相关数据，它将创建一个圆形对象图。 有关如何处理它的更多信息，请检查以下内容：http://www.asp.net/web-api/overview/data/using-web-api-with-entity-framework/part-4