实体框架插入已存在于数据库中的实体

Question

我正在使用 EF 6 Code-First MVC plus Identity

我自定义了 Identity 框架中定义的标准 ApplicationUser 类，当我尝试通过我的网页注册新用户时，EF 尝试插入数据库中已经存在的实体。

//some code above here

using (ApplicationDbContext db = new ApplicationDbContext())
{
    // I load the City object form db based on the model passed to current method
    City city = db.Countries.Include("States.Cities")
        .First(c => c.Code == model.CountryCode)
        .States.First(s => s.Id == model.StateId)
        .Cities.First(ci => ci.Name == model.CityName);

    // I create a new Employee and a new Company and Company has an Address 
    // referring to the City I loaded from db
    Employee employee = new Employee
    {
        FirstName = model.FirstName,
        LastName = model.LastName,
        Company = new Company
        {
            Name = model.CompanyName,
            OfficePhone = model.OfficePhone,
            Address = new Address { City = city, Street = model.Street, ZipCode = model.ZipCode }
        }
    };

    // This is part of Identity framework code
    var user = new ApplicationUser
    {
        UserName = model.Email,
        Email = model.Email,
        // my custom code: I assign employee to the standard ApplicationUser class
        UserProfile = employee
    };

    // This is going to save the new user to database, 
    // but it tries to insert a new Country object into db. 
    // Note that City class has a property of type State 
    // and State class has a property type of Country 
    var result = await UserManager.CreateAsync(user, model.Password);

    // more code below

根据我得到的错误，听起来 EF 正在将 Country 实体插入到数据库中。我猜当 EF 将地址添加到 db 时会发生这种情况。在我的代码中，Address 是新对象，但 City、State 和 Country 已经存在，您会看到我一开始是从 db 加载 City。所以我尝试使用下面的代码，但它没有帮助：

db.Entry(employee.Company.Address.City).State = EntityState.Unchanged;

抱歉，代码太长了，不过我尽量减少它。

这是我的模型：

public class Country
{
    string Code;
    string Name;
    List<State> States;
}

public class State
{
    int Id;
    string Name;
    List<City> Cities;
}

public class City
{
    int Id;
    string Name;
    State State;
}

public class Address
{
    string Street;
    string ZipCode;
    City City;
}

public class Company
{
    string Name;
    string OfficePhone;
    Address Address;
}

Answer 1

我很久以前就遇到过类似的问题。我不知道问题所在，但我有一个解决方法：

替换代码：

var result = await UserManager.CreateAsync(user, model.Password);

下面的代码：

var UserManager = new UserManager<ApplicationUser>(new UserStore<ApplicationUser>(db));
var result = UserManager.Create(user, model.Password);

这将正确保存数据。

Answer 2

问题是，您每次都在创建新对象。您需要先执行测试以查看用户是否存在，如果存在则使用现​​有数据填充对象并使用更新。所以你还需要考虑使用UserManager.UpdateAsync方法。