How to merge two ILists together

Question

I have two ILists in my which are getting values from the separate tables within the database. These tables contain the same columns and values but for other reasons the client needs them stored in separate tables.

private IList<MeterReadingDto> _meterReadings;
private IList<PseudoReadingDto>  _pseudoReading;
public IList<MeterReadingDto> MeterReadings
    {
        get
        {
            return _meterReadings != null ? _meterReadings.OrderByDescending(x => x.ReadDate).ToList() : null;
        }
        set { _meterReadings = value; }
    }

    public IList<PseudoReadingDto> PseudoReadings
    {
        get
        {
            return _pseudoReading != null ? _pseudoReading.OrderByDescending(x => x.ReadDate).ToList() : null;
        }
        set { _pseudoReading = value; }
    }

As you can see they both get the results and store them, but i now need to merge/union these list so that they can be displayed in one table. Any ideas on how to do this

Answer 1

Consider using the IEnumerable method extension Union.

NOTE: Using this operation will result in duplicate elements between the two collections being removed from the result.

Answer 2

Well, if you can extract an interface (or ever a base class) for MeterReadingDto and PseudoReadingDto, than you could merge them to a IEnumerable or IList of that.

i.e.

public IEnumerable<BaseReadingDto> AllReadings {
  get{
    return MeterReadings.Concat(PseudoReadings);
  }
}

Answer 3

You need to be able to treat both PseudoReadingDto and MeterReadingDto as the same object type. You could look into anonymous types, but I suggest having both implement the same interface (like maybe IReadingDto). Then you can create a new List<IReadingDto> and combine the lists.

If they share the same type, you can use List.AddRange() to append the lists together.