public async Task <OperationResult> UpdateFriends(Guid userId, IEnumerable <Guid> friendIds)
{
var entity = new DynamicTableEntity(UserEntity.FormatPartitionKey(userId), UserEntity.FormatRowKey())
{
ETag = "*"
};
entity.Properties.Add(nameof(UserEntity.FriendsJson), new EntityProperty(UserEntity.FormatFriendsJson(friendIds)));
await db.UserTable.ExecuteAsync(TableOperation.Merge(entity));
return(OperationResult.Success);
}