c# - 如何使用 Entity Framework 从另一个类返回 ID 或全部？

Question

我正在学习 Entity Framework ，所以如果这对你来说很容易，请不要责怪我

我有类(class)HomeNumber.cs

    [ScaffoldColumn(false)]
    [Key]
    public int HomeNumberId { get; set; }
    //[ForeignKey("HomeNumberId")]
    //public virtual HomeNumber HomeNumbers { get; set; }

    [Required(ErrorMessage = "Polje kućni broj je obavezno!")]
    public string HomeNumberName { get; set; }

    [Required(ErrorMessage = "Polje pod broj/slovo je obavezno!")]
    public string HomeSubNumber { get; set; }

    public int StreetId { get; set; }
    [ForeignKey("StreetId")]
    public virtual Street Street { get; set; }

    ....

    public bool AddHomeNumber(string homeNumberName, string homeSubNumber, Street street)
    {
        HomeNumber number = new HomeNumber();
        number.HomeNumberName = homeNumberName;
        number.HomeSubNumber = homeSubNumber;
        number.StreetId = street.StreetId;

        using (var _db = new DataContext())
        {
            // Dodaj HomeNumber u bazu [AD_HOMENUMBER]
            _db.DB_HomeNumber.Add(number);
            _db.SaveChanges();
        }
        // Success.
        return true;
    }

以及 Street.cs 类

    [ScaffoldColumn(false)]
    [Key]
    public int StreetId { get; set; }

    [Required(ErrorMessage = "Polje naziv ulice je obavezno!")]
    public string StreetName { get; set; }

    .....

    public bool AddStreet(string streetName)
    {
        Street street = new Street();
        street.StreetName = streetName;

        using (var _db = new DataContext())
        {
            // Dodaj Street u bazu [AD_STREET]
            _db.DB_Street.Add(street);
            _db.SaveChanges();
        }
        // Success.
        return true;
    }

我的后台代码是:

    Street st = new Street();
    st.AddStreet(ucAddress.Street.Text);

    HomeNumber hou = new HomeNumber();
    hou.AddHomeNumber(ucAddress.HouseNumber.Text, ucAddress.HouseSubNumber.Text, st.StreetId);

我需要在我的后台代码 st.streetId 中提供值，...我不知道我缺少什么，...因为在 AddHomeNumber 中我调用 < strong>street.StreetId 其中是 st.streetId

的返回值

Answer 1

我认为您想要在 AddStreet 上执行的操作如下所示。您保存Street并返回结果。

public Street AddStreet(string streetName)
{
    Street street = new Street();
    street.StreetName = streetName;

    using (var _db = new DataContext())
    {
        // Dodaj Street u bazu [AD_STREET]
        _db.DB_Street.Add(street);
        _db.SaveChanges();
    }
    // Success.
    return street;
}

在后面的代码中，您在 AddHomeNumber 中传递了 st 而不是 st.StreetId。

Street st = new Street();
st = st.AddStreet(ucAddress.Street.Text); // get the street that has been saved with generated id.

HomeNumber hou = new HomeNumber();
hou.AddHomeNumber(ucAddress.HouseNumber.Text, ucAddress.HouseSubNumber.Text, st);

注意:我建议您看看存储库模式，这将使您的生活更轻松，并且您将编写出更具可读性和更出色的代码。

---

Street 的基本存储库对于 HomeNumber 或您以相同方式创建存储库的其他实体来说也将是这样的。 p>

public class StreetRepository 
{
    private DataContext _db;
    public StreetRepository(DataContext dataContext)
    {
        _db = dataContext;
    }

    public Street Add(string streetName)
    {
        Street street = new Street();
        street.StreetName = streetName;

        using (var _db = new DataContext())
        {
            // Dodaj Street u bazu [AD_STREET]
            _db.DB_Street.Add(street);
            _db.SaveChanges();
        }
        // Success.
        return street;
    }

    public Street Get(int id)
    {
        return _db.DB_Street.Find(id);
    }

    // other CRUD methods
}

用法:

StreetRepository streetRepository = new StreetRepository();
HomeNumberRepository homeNumberRepository = new HomeNumberRepository(); // you have to create it yourself

Street st = streetRepository.Add(ucAddress.Street.Text); // get the street that has been saved with generated id.

HomeNumber homeNumber = homeNumberRepository.Add(ucAddress.HouseNumber.Text, ucAddress.HouseSubNumber.Text, st);

注意:您可能会发现为每个实体编写一个存储库很痛苦，这里有帮助通用存储库 em>.

掌握存储库模式后，您可以转到工作单元并发现EntityFramework已经拥有它。