(使用Entity Framework 6.2)
我有以下两个模型/实体:
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; }
}
以下DbContext
public DbSet<Country> Countries { get; set; }
我的问题是:如果国家/地区对象的子项发生变化(即城市),我该如何更新?
我可以这样做:
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();
}
那会有用吗?或者我应该专门添加每个城市?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();
}
答案 0 :(得分:6)
您需要将Cities
添加到正在更新的特定Country
对象。
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;}
}
希望它有所帮助。