更新的孩子在實體框架對象6

Question

（使用實體框架6.2）

我有以下兩種型號/實體：

public class City 
    { 
     public int CityId { get; set; } 
     public string Name { get; set; } 
    } 

public class Country 
    { 
     public Country() 
     { 
      Cities new HashSet<City>(); 
     } 

     public int CountryId { get; set; } 
     public string Name { get; set; } 
     public virtual ICollection<City> Cities { get; set; } 
    } 

而下面的DbContext

public DbSet<Country> Countries { get; set; } 

我的問題是：如果國家對象的孩子改變了（即城市），我該如何更新？

我可以這樣做：

List<City> cities = new List<City>(); 
// Add a couple of cities to the list... 
Country country = dbContext.Countries.FirstOrDefault(c => c.CountryId == 123); 
if (country != null) 
{ 
    country.Cities.Clear(); 
    country.Cities = cities; 
    dbContext.SaveChanges(); 
} 

將這項工作？或者我應該專門添加每個城市？即：

List<City> cities = new List<City>(); 
// Add a couple of cities to the list... 
Country country = dbContext.Countries.FirstOrDefault(c => c.CountryId == 123); 
if (country != null) 
{ 
    country.Cities.Clear(); 
    foreach (City city in cities) 
     country.Cities.Add(city); 
    dbContext.SaveChanges(); 
} 

Answer 1

您需要添加Cities的正在更新特定Country對象。

public Country Update(Country country) 
{ 
    using (var dbContext =new DbContext()) 
    { 
     var countryToUpdate = dbContext.Countries.SingleOrDefault(c => c.Id == country.Id); 
     countryToUpdate.Cities.Clear(); 
     foreach (var city in country.Cities) 
     { 
      var existingCity = 
       dbContext.Cities.SingleOrDefault(
        t => t.Id.Equals(city.cityId)) ?? 
       dbContext.Cities.Add(new City 
       { 
        Id = city.Id, 
        Name=city.Name 
       }); 

      countryToUpdate.Cities.Add(existingCity); 
     } 
     dbContext.SaveChanges(); 
     return countryToUpdate; 
    } 
} 

更新：

public class City 
    { 
     public int CityId { get; set; } 
     public string Name { get; set; } 

     [ForeignKey("Country")] 
     public int CountryId {get;set;} 
     public virtual Country Country {get; set;} 
    } 

希望它能幫助。