Lambda Expression for Finding properties

Question

I want to retreive LineOfBusiness property from promotionCatalogResponseRootObject where PromotionID is equal to myId

public class PromotionCatalogResponseRootObject
{
   public PromotionCatalogResponse PromotionCatalog { get; set; }
}

public class Promotion
{
  public string PromotionId { get; set; }
  public string LineOfBusiness { get; set; }
  public string PromotionName { get; set; }
}

public class PromotionCatalogResponse
{
  public List<Promotion> Promotion { get; set; }
}

I started off like this but I know I'm doing it wrong. Please guide

string myId = "7596";
string lineOfBusiness = dataPromotionCatalog.PromotionCatalog
                                            .Promotion.Find(p => p.LineOfBusiness);

Sebastian Brosch · Accepted Answer · 2017-09-29 17:05:36Z

7

What you are missing is the the Find method is expecting to receive a predicate with a bool return value but you are returning a string, the LineOfBusiness property.

First filter the items you want and then select the desired property. In addition, I'd go with the Where instead of the Find. (Find() vs. Where().FirstOrDefault())

var result = dataPromotionCatalog.PromotionCatalog.Promotion
                                 .Where(i => i.PromotionId == myId)
                                 .Select(i => i.LineOfBusiness);

or in query syntax

var result = (from item in dataPromotionCatalog.PromotionCatalog.Promotion
              where item.PromotionId == myId
              select item.LineOfBusiness);

If you are expecting/want to have one item then use FirstOrDefault:

var result = dataPromotionCatalog.PromotionCatalog.Promotion
                 .FirstOrDefault(i => i.PromotionId == myId)?.LineOfBusiness;

edited Sep 29, 2017 at 17:05

Sebastian Brosch

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answered Nov 1, 2016 at 12:12

Gilad Green

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2 Comments

Huma Ali Over a year ago

What if I dont use ?. and just use . ?

Gilad Green Over a year ago

@HumaAli Then in the case that no item was found you will get a NullReferenceException. Check link I gave about Null propagation

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