实体框架核心，如何为.HasOptional配置可空的外键等效项

Question

我需要配置可选/可空的外键。在我的场景中，ParkingAttendant与HandHeldDevice的关系是0:*。我已经设置了configuration类，但不确定是否正确？

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public class HandheldDevice 
{
    // other properties
    public int ParkingAttendantId { get; set; }

    public ParkingAttendant ParkingAttendants { get; set; }        
}

public class ParkingAttendant 
{
    public ParkingAttendant()
    {
        this.HandheldDevices = new HashSet<HandheldDevice>();
    }

    // other properties
    public ICollection<HandheldDevice> HandheldDevices { get; set; }
}

配置类

public class HandHeldDeviceConfiguration : IEntityTypeConfiguration<HandheldDevice>
{
    public void Configure(EntityTypeBuilder<HandheldDevice> builder)
    {
        builder.ToTable("mytable", "dbo");

        builder.HasKey(column => column.HandHeldId);

        builder
            .HasOne(handHeldDevice => handHeldDevice.ParkingAttendants)
            .WithMany(pakingAttendant => pakingAttendant.HandheldDevices)
            .HasForeignKey(handHeldDevice => handHeldDevice.ParkingAttendantId)
            .IsRequired(false);
    }
}

Answer 1

要使可选HandheldDevice成为可空的，请将ParkingAttendantId设置为可空。另外，通过添加主键来修复您的类，并再次尝试迁移到db。如果您使用EF核心5+，则不需要任何流畅的apis

public class HandheldDevice 
{
 public int Id { get; set;

    public int? ParkingAttendantId { get; set; }

    public  virtual ParkingAttendant ParkingAttendant { get; set; }        
}

public class ParkingAttendant 
{
    public int Id { get; set;

    public ParkingAttendant()
    {
        this.HandheldDevices = new HashSet<HandheldDevice>();
    }
    
    public virtual ICollection<HandheldDevice> HandheldDevices { get; set; }
}