如何通过值转换修改属性上的 EntityState？

Question

我使用 ValueConverter 将自定义属性类型（列表）映射到字符串。转换工作完美，但我无法将 EntityState 设置为已修改，因为 EF 找不到实体。

当我修改列表时，EF 不会检测到更改，这是 expected。但是，当我尝试手动更改状态时，出现错误

The entity type 'List<List<Reward>>' was not found. Ensure that the entity type has been added to the model.

我发现的唯一解决方法是将属性设置为列表的克隆，这并不理想。

model.PropertyName = new List<Reward>(model.PropertyName); // clone the list

下面是一些示例代码：

public class RewardContainer
{
    public List<List<Reward>> Rewards { get; set; }
}

// db context
protected override void OnModelCreating(ModelBuilder builder)
{
    // use custom conversion, which is working fine
    builder.Entity<RewardContainer>().Property(p => p.Rewards).HasConversion(ValueConverters.GetJsonConverter<List<List<Reward>>>());
}

// controller
public async Task ModifyProperty()
{
    rewardContainer.Rewards[0].Add(someReward);

    // try to manually change the EntityState...
    dbContext.Entry(rewardContainer.Rewards).State = EntityState.Modified;
    // error: The entity type 'List<List<Reward>>' was not found. Ensure that the entity type has been added to the model.        

    await dbContext.SaveChangesAsync();
}

Answer 1

除了 ValueConverter 之外，还使用 ​​ValueComprarer 使 EF 能够跟踪转换后的实体。

public static class ValueConversionExtensions
{
    public static PropertyBuilder<T> HasJsonConversion<T>(this PropertyBuilder<T> propertyBuilder) where T : class, new()
    {
        ValueConverter<T, string> converter = new ValueConverter<T, string>
        (
            v => JsonConvert.SerializeObject(v),
            v => JsonConvert.DeserializeObject<T>(v) ?? new T()
        );

        ValueComparer<T> comparer = new ValueComparer<T>
        (
            (l, r) => JsonConvert.SerializeObject(l) == JsonConvert.SerializeObject(r),
            v => v == null ? 0 : JsonConvert.SerializeObject(v).GetHashCode(),
            v => JsonConvert.DeserializeObject<T>(JsonConvert.SerializeObject(v))
        );

        propertyBuilder.HasConversion(converter);
        propertyBuilder.Metadata.SetValueConverter(converter);
        propertyBuilder.Metadata.SetValueComparer(comparer);

        return propertyBuilder;
    }
}