Deleting duplicates references in list c#

Question

I have trouble deleting the duplicate references in my list.

I have this list

List<SaveMongo> toReturn

with my class SaveMongo that looks like this

  public class SaveMongo
{
    public ObjectId _id { get; set; }
    public DateTime date { get; set; }
    public Guid ClientId { get; set; }
    public List<TypeOfSave> ListType = new List<TypeOfSave>();
    public List<ObjectId> ListObjSave = new List<ObjectId>();
    public SaveMongo()
    { }
}

Whenever I want to add an element to my list I use the following code

public static fctName(BsonDocument doc)
{
    toReturn.Add(AddingSaveMongo(doc.GetValue("_id")));
}

public static SaveMongo AddingSaveMongo(BsonValue ObjValue)
{
    foreach (SaveMongo doc in SpeCollection.FindAll())
    {
        foreach (var id in doc.ListObjSave)
        {
            if (id == ObjValue)
                return (doc);
        }
    }
    return (null);
}

However, I sometimes get duplicates references. I tried using this

toReturn = toReturn.Distinct().ToList();

to delete them. Without success.

I also tried to do this

if (!toReturn.Contains(AddingSaveMongo(doc.GetValue("_id"))))
   toReturn.Add(AddingSaveMongo(doc.GetValue("_id")));

Still without success. But whenever I print the references in my list I get those result

What I am missing here so that I still have duplicates references in my List ?

Answer 1

Currently, Distinct is matching your objects using object.Equals, which is doing reference equality. One way to tell it to match objects based on other criteria is by implementing IEquatable<SaveMongo>. This example compares objects based on their Id:

public class SaveMongo : IEquatable<SaveMongo>
{
    public ObjectId _id { get; set; }
    public DateTime date { get; set; }
    public Guid ClientId { get; set; }
    public List<TypeOfSave> ListType = new List<TypeOfSave>();
    public List<ObjectId> ListObjSave = new List<ObjectId>();

    public override bool Equals(object obj)
    {
        if (ReferenceEquals(null, obj)) return false;
        if (ReferenceEquals(this, obj)) return true;
        if (obj.GetType() != this.GetType()) return false;
        return Equals((SaveMongo) obj);
    }

    public override int GetHashCode()
    {
        return _id.GetHashCode();
    }

    public bool Equals(SaveMongo other)
    {
        return _id.Equals(other._id);
    }
}

Answer 2

Use grouping:

toReturn = (from e in toReturn
            group e by e._id into g
            select g.First()).ToList();

Also, you can group by two (or more) fields:

toReturn = (from e in toReturn
            // group by ID and Date component
            group e by new { e._id, e.date.Date } into g
            select g.First()).ToList();