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Question

I have an observable collection of Bids, class structure below.

public class Bids
{       
        public DateTime StartDateTimeLocal { get; set; }
        public DateTime EndDateTimeLocal { get; set; }                

        public decimal Bid5 { get; set; }
    public decimal Price5  { get; set; }
        public decimal Bid4 { get; set; }
    public decimal Price4  { get; set; }
        public decimal Bid3 { get; set; }
    public decimal Price3  { get; set; }
        public decimal Bid2 { get; set; }
    public decimal Price2  { get; set; }
        public decimal Bid1 { get; set; }
    public decimal Price1  { get; set; }
}

I have an observable collection

public ObservableCollection<Bid> Bids {get; set;}

Bids collection looks like below,

StartDateTimeLocal EndDateTimeLocal Bid5 Price5 Bid4 Price4 Bid3 Price3 Bid2 Price2 Bid1 Price1
2014-02-14 23:00 2014-02-14 23:30 0 0 0 0 0 0 50 10 100 100
2014-02-14 23:30 2014-02-15 00:00 0 0 0 0 0 0 10 300 200 10
2014-02-15 00:00 2014-02-15 00:30 0 0 0 0 0 0 100 30 0 10
2014-02-15 03:00 2014-02-15 01:00 0 0 0 0 0 0 30 100 0 0

I need to validate the data in the observable collection is valid as per the rules...

1. Bid 2 should only have a value if bid 1 has a value. So, unless there is a bid 1 a non zero value in bid 2 is invalid. Similarly a a value in bid1, bid2, bid3 is fine but if bid4 doesn't have a value then a value in bid5 is invalid.
2. Bid prices must be constant or increasing as you go up bids. So, bid 2 price should either be same or greater than bid 1 price.

In the above sample, - The 3rd & 4th row are incorrect since Bid1 doesn't have a value but Bid2 does.
- The 2nd row is correct since Bid1 has a value and hence Bid2 having a value is fine, The price of Bid2 > Bid1. While Row 1 is
incorrect since Price of Bid 2 is < Price of Bid 1

Can some one please advise an approach to perform this validation.

Answer 1

The Bids object itself is not a collection (does not implement any LINQ-related interface, like IEnumerable), so I have no idea why you're trying to use LINQ to validate the object.

Yes, you can use LINQ to check if all items in that particular ObservableCollection<Bids> are OK

var areAllOK = source.All(x => IsValid(x));

You can get only these, which are valid:

var validItems = source.Where(x => x.IsValid(x));

or only these which are not valid:

var invalidItems = source.Where(x => !x.IsValid(x));

But you have to write IsValid method, and I cannot see how it could use LINQ internally.

Answer 2

The bid values will need to be enumerable to perform a LINQ-based validation. Why not just make the bid values an observable collection as well? If you really have a good reason for each value to be a separate property, you could create the enumerable this way:

public IEnumerable<decimal> Values {
    get {
        yield return Bid1;
        yield return Bid2;
        yield return Bid3;
        yield return Bid4;
        yield return Bid5;
    }
}

For the validation, you would probably want a "sliding window". There is nothing included in LINQ for this, but some ideas are given in this answer. The easiest is to Zip {1, 2, 3...} with {2, 3, 4...}:

var pairs = Values.Zip(Values.Skip(1), (previous, current) => new {previous, current});

Then validate with All:

var isValid = pairs.All(p => p.previous != 0 && p.current >= p.previous);