获取动态 object 而不是从 .net 核心 Z240AA2CEC4B29C56F3BEE520A8DCEE7 中的 MongoDB 强类型

Question

I try to use MongoDB in combination with .net core (c#) to save some survey results.

The challenge is that I plan to make it as generic as possible to be able to add other rating controls later.

I am able to save different result types in one table.

public class VoteBase
{
    [BsonId]
    [BsonRepresentation(BsonType.ObjectId)]
    public string Id { get; set; }
    public User User { get; set; }
    public Control Control { get; set; }
    public string ControlType { get; set; }
}



public class VoteStarRatingControl : VoteBase
{
    public int? Rating { get; set; }
}



public class VoteStarRatingWithComment : VoteStarRatingControl
{
    public string Comment { get; set; }
}

I created a table of base type as MongoCollection:

        private readonly IMongoCollection<VoteBase> _voteBases;

To save it to that collection I used this code (where the DTO is same content datatransfer object to decouple the REST service from DB structure):

List<VoteBase> dbVotes = new List<VoteBase>();

foreach (VoteBaseDTO v in votes)
{
    switch (v) {
        case VoteStarRatingWithCommentDTO src:
            dbVotes.Add(new VoteStarRatingWithComment() { User = new User() { Id = UserId }, Control = new Control() { Id = src.ControlId }, Rating = src.Rating, Comment = src.Comment });
            break;
        case VoteStarRatingControlDTO sr:
            dbVotes.Add(new VoteStarRatingControl() { User = new User() { Id = UserId }, Control = new Control() { Id = sr.ControlId }, Rating = sr.Rating });
            break;
    }

}

_voteBases.InsertMany(dbVotes);

return dbVotes;

Until here all works fine.

Now I try to get the votes back for a specific list of controls (for one survey).

The following command fails with

'Element 'Rating' does not match any field or property of class SurveyToolRestAPI.Models.VoteBase.'

 object obj = _voteBases.Find(vb => vb.Control.Id == "5e9c24c50a099728b027e176").SingleOrDefault();

This is because it is of Type StarRatingControl instead of type VoteBase.

Is there a way to get the list as dynamic instead of strong typed from a MongoDB collection?

Answer 1

Thanks Eldho, you pointed me to the right direction.

Doings some more research with the Bson... attributes I found the solution finally in this post Mongodb collection as dynamic

The key is to add a BsonKnownTypes attribute. The it can be used as strong typed collection and the list will contain the appropriate subtypes.

    [BsonKnownTypes(typeof(VoteBase), typeof(VoteStarRatingControl), typeof(VoteStarRatingWithComment))]