Question

我在使用EF.Core中的1to1关系时遇到了一些麻烦，

我有这些模特：

public class IncomingData
{
    [Key]
    [Required]
    public int Id { get; set; }

    ...

    public History History { get; set; }
}

public class History
{
    [Key]
    public int Id { get; set; }

    ...

    [ForeignKey("IncomingDataId")]
    public IncomingData IncomingData { get; set; }
}

历史数据库似乎正确地将ForeignKey存储为IncommingDataId

但是当我在控制器中执行以下代码时

var histories = _db.Histories.Where(x => x.IMEI == device.IMEI).OrderByDescending(x => x.Timestamp);

histories.IncomingData始终为null

所以我必须做一些 hackish 解决方法让histories包含IncomingData

foreach (var h in histories) {
    var incomingDataRecord = _db.IncomingData.FirstOrDefault(x => x.History == h);
}

我相信我在某处做错了:)如果需要信息，我会添加

Answer 1

您不包含相关的实体对象。

Kotlin

    //Form 1
    public partial class BasketScreen : Form
    {
        private void PurchaseButton_Click(object sender, EventArgs e)
        {
            // show the purchase products screen.
            this.Hide();
            PurchaseScreen ps = new PurchaseScreen();
            ps.Show();
        }  
    }



    //UniqueNumber is the number i wish to display.
    //OrderNumber is the name of the label where i want to display the UniqueNumber

    //form 2
    public partial class PurchaseScreen : Form
    {
        //private int UniqueNumber = 0;  This was the issue

        //This line was the fix.
        private static int UniqueNumber = 0;
    }

    private void PurchaseScreen_Load(object sender, EventArgs e)
    {
        UniqueNumber++;
        OrderNumber.Text = UniqueNumber.ToString("000");
    }

    private void BackButton_Click(object sender, EventArgs e)
    {
        this.Hide();
        BasketScreen bs = new BasketScreen();
        bs.Show();
    }

Answer 2

我认为History类应该是这样的：

public class History
{
    [Key]
    public int Id { get; set; }

    [ForeignKey(nameof(Id))]
    public IncomingData IncomingData { get; set; }
}

这意味着，您使用相同的属性（Id）来引用这两个实体。如果可以，您可以通过分配[Column]属性为其指定不同的名称。

Answer 3

没有运行它不是100％确定，但我认为你正在寻找这个...

public class IncomingData
{
[Key]
[Required]
public int Id { get; set; }

...

public History History { get; set; }
}

public class History
{
[Key]
public int Id { get; set; }

...

[InverseProperty("Id")]
public IncomingData IncomingData { get; set; }
}

然后用...

检索它

var histories = _db.Histories.Where(x => x.IMEI == device.IMEI).Include("IncomingData").OrderByDescending(x => x.Timestamp);

假设IMEI和Timestamp是History

的属性

EF.Core查询相关数据

3 个答案: