c# - Entity Framework 6 上的数据库迁移问题

Question

我有以下类(class)(为简洁起见缩短)；

public class InsurancePolicy : AuditableEntity<int>
{
    [Column("id"), Key]
    public override int ID { get; set; }
    [Column("deviceid"), ForeignKey("Device")]
    public int DeviceId { get; set; }
    public virtual Device Device { get; set; }
}

public partial class Device : AuditableEntity<int>
{
    [Column("deviceid"), Key]
    public override int ID { get; set; }

    [ForeignKey("Policy")]
    public int PolicyId { get; set; }
    public virtual InsurancePolicy Policy { get; set; }

    [ForeignKey("Vehicle")]
    public int VehicleId { get; set; }
    public virtual Vehicle Vehicle { get; set; }
}

public partial class Vehicle : AuditableEntity<int>
{
    [Column("id"), Key]
    public override int ID { get; set; }

    [Column("deviceid"), ForeignKey("Device")]
    public int DeviceId { get; set; }
    public virtual Device Device { get; set; }

    public virtual List<InsurancePolicyVehicle> InsurancePolicyVehicles { get; set; }
}

现在，当我尝试运行我的 update-database 命令时，出现此错误:

Device_Policy_Target: : Multiplicity is not valid in Role 'Device_Policy_Target' in relationship 'Device_Policy'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.

Device_Vehicle_Target: : Multiplicity is not valid in Role 'Device_Vehicle_Target' in relationship 'Device_Vehicle'. Because the Dependent Role properties are not the key properties, the upper bound of the multiplicity of the Dependent Role must be '*'.

谁能告诉我这里做错了什么？

Answer 1

以 Device_Policy_Target 关系为例，您有以下内容(缩减为该关系的相关属性):

public class InsurancePolicy : AuditableEntity<int>
{   
    [Column("id"), Key]
    public override int ID { get; set; }
    [Column("deviceid"), ForeignKey("Device")]
    public int DeviceId { get; set; }
    public virtual Device Device { get; set; }
}

public partial class Device : AuditableEntity<int>
{
    [Column("deviceid"), Key]
    public override int ID { get; set; }

    [ForeignKey("Policy")]
    public int PolicyId { get; set; }
    public virtual InsurancePolicy Policy { get; set; }

}

您在这里定义的是一对一关系。 EF 仅支持两个表共享主键的这种关系。在您的配置中，您的子表 - InsurancePolicy 有自己的 PK 和 Device 的外键。 EF 仅支持具有这些约束的一对多关系。

要将这些关系定义为一对一，请将您的设置切换为以下内容:

public class InsurancePolicy : AuditableEntity<int>
{
    [Column("deviceid"), Key, ForeignKey("Device")]
    public override int ID { get; set; }
    public virtual Device Device { get; set; }
}

public partial class Device : AuditableEntity<int>
{
    [Column("deviceid"), Key]
    public override int ID { get; set; }

    public virtual InsurancePolicy Policy { get; set; }    
}

部分原因是 EF 不支持唯一约束。 This article使用 DataAnnotations 对一对一关系进行了更全面的解释

更新:

要使用您拥有的表/键“伪造”一对一，然后考虑这样的事情:

public class InsurancePolicy : AuditableEntity<int>
{   
    [Column("id"), Key]
    public override int ID { get; set; }
    [Column("deviceid"), ForeignKey("Device")]
    public int DeviceId { get; set; }
    public virtual Device Device { get; set; }
}

public partial class Device : AuditableEntity<int>
{
    [Column("deviceid"), Key]
    public override int ID { get; set; }

    public virtual IEnumerable<InsurancePolicy> PoliciesAsList { get; set; }

    [NotMapped]
    public virtual InsurancePolicy Policy {
        get {
            return (PoliciesAsList != null) 
                ? PoliciesAsList.FirstOrDefault() 
                : null;                
        }
    }

}

在这种情况下，我任意选择了 Device 作为父级——您选择哪个并不重要。

您还应确保数据库对 InsurancePolicy 表上的 deviceid 具有唯一约束。