Problem with update master detail entity

Hi, I have a problem with an update in a master-detail entity, master is News and detail is ContentRelations. and I user CRUDAsyuncService and Update method and pass it master entity. this is my code:

    public class News : Content
    {
        public string Description { get; set; }
        public string Body { get; set; }
        public DateTime PublishDate { get; set; }
        public bool IsPromoted { get; set; }
        public DateTime? PromotionExpireDate { get; set; }
    }

    public abstract class Content : FullAuditedEntity<int, User>, IPassivable, INeedCrudPermissions
    {
        public string Title { get; set; }
        public bool IsActive { get; set; }
        public virtual ContentProtection ContentProtection { get; set; }
        public virtual ICollection<ContentRelation> ContentRelations { get; set; } = new 
        List<ContentRelation>();
    }

I got this error:

e.InnerException {System.Data.SqlClient.SqlException (0x80131904): Cannot insert explicit value for identity column in table ‘ContentRelations’ when IDENTITY_INSERT is set to OFF.

[maliming]

@mehdih66 If you want to update entities and child entities within a single method.

Fake code:

public override News Update(News input)
{
	var news = await Repository.GetAsync(input.Id);
	ObjectMapper.Map(input, news); //ignore the fileRelations.

	foreach (var file in input.fileRelations)
	{
		var dbFile = await Repository.GetAsync(file.Id);
		ObjectMapper.Map(file, dbFile);
	}
	
	return news;
}

[mehdihadeli]

Ok thanks