How to modify EntityState on property with value conversion?

asp.net-core entity-framework-core

Question

I use ValueConverter to map custom property type (List) to string. The conversion works perfectly, but I cannot set the EntityState to modified, because EF does not find the entity.

When I modify the list, EF does not detect changes, which is exptected. However, when I try to change the state manually, I get error

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

Only workaround I have found is to set the property to clone of the list, which is not ideal.

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

Here is some sample code:

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();
}
1
0
2/12/2019 3:40:17 PM

Popular Answer

Using a ValueComprarer in addition to ValueConverter enables EF to track the converted entity.

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;
    }
}
3
2/14/2019 9:34:33 AM


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