实体框架代码优先，错误:"EntityType 'OfferSequence'没有定义键

我首先使用实体框架代码。我正在尝试创建一个名为OfferSequence的新实体，以便在数据库中自动创建表。

问题是，当我尝试用新实体更新数据库时，我得到以下错误

在模型生成过程中检测到一个或多个验证错误:

ERP.EnterpriseDataAccessLayer.EnterpriseData。OfferSequence::EntityType 'OfferSequence'没有定义键。为此定义键EntityType。OfferSequences: EntityType: EntitySet 'OfferSequences' is基于没有定义键的'OfferSequence'类型。

但是，正如您在下面看到的，键在属性SequenceStart 上被清楚地定义了

public class OfferSequence : IEntity<OfferSequence>
{
    public OfferSequence(uint sequenceStart, uint incrementalCounter, uint annualIncrementalCounter)
    {
        Validate.EnsureIsTrue(incrementalCounter >= sequenceStart && annualIncrementalCounter >= sequenceStart, "Counters can not be lower than sequence start");
        SequenceStart = sequenceStart;
        IncrementalCounter = incrementalCounter;
        AnnualIncrementalCounter = annualIncrementalCounter;
        LastUpdateDate = DateTime.UtcNow;
    }
    [Key]
    public uint SequenceStart { get; private set; }
    public uint IncrementalCounter { get; private set; }
    public uint AnnualIncrementalCounter { get; private set; }
    public DateTime LastUpdateDate { get; private set; }
    public OfferSequence Clone()
    {
        OfferSequence copy = new OfferSequence(SequenceStart, IncrementalCounter, AnnualIncrementalCounter);
        return copy;
    }
    object ICloneable.Clone()
    {
        return Clone();
    }
    public void Modify(OfferSequence obj)
    {
        AnnualIncrementalCounter = obj.AnnualIncrementalCounter;
        IncrementalCounter = obj.IncrementalCounter;
        LastUpdateDate = DateTime.UtcNow;
    }
}