FIND items in list using lambda expression

Question

I have following classes:

public class AuthenticateCustomerResponse
{
    public EligiblePromotions EligiblePromotions { get; set; }
}

public class EligiblePromotions
{
    public List<PromotionList> PromotionList { get; set; }
}
public class PromotionList
{
    public string LineOfBusiness { get; set; }
    public AuthenticatePromotions Promotions { get; set; }
}
public class AuthenticatePromotions
{
    public List<AuthenticatePromotion> Promotion { get; set; }
}
public class AuthenticatePromotion
{
    public string ServiceType { get; set; }
}

I want to retrieve PromotionList whose LineOfBusiness is equal to "VID" and ServiceType is equal to "SAT". I tried following lambda expression:

PromotionList getPromotion = AuthenticateCustomerResponse.EligiblePromotions.PromotionList.Find(p => p.LineOfBusiness.ToUpper().Equals("VID")).Promotions.Promotion.Find(o=>o.ServiceType.Equals("SAT"));

but I'm getting error:

Cannot implicitly convert type 'AuthenticatePromotion' to 'PromotionList'

What am I doing wrong?

The naming of your properties and class names is terrible. Use FirstOrDefault or Where it will be easier. — mybirthname
– mybirthname, Commented Dec 2, 2016 at 10:09
You are retrieving an AuthenticatePromotion object from your Promotion list. If you only want the PromotionList, why do you have another Find? — user4189129
– user4189129, Commented Dec 2, 2016 at 10:11

user4189129 · Accepted Answer · 2016-12-02 10:13:43Z

8

The code below will get you the first object whose LineOfBusiness equals to 'VID'.

var promotionList = AuthenticateCustomerResponse.EligiblePromotions.PromotionList
.Where(p => p.LineOfBusiness.ToUpper().Equals("VID")).FirstOrDefault();

You can use .ToList() if you want all objects that have VID as LineOfBusiness instead of .FirstOrDefault()

Edit: You can add another clause to your .Where() if you want to check for the SAT

answered Dec 2, 2016 at 10:13

user4189129

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3 Comments

zaria khan Over a year ago

Cannot implicitly convert type 'System.Collections.Generic.List<PromotionList>' to 'PromotionList'

user4189129 Over a year ago

ToList returns in a list of objects which pass your Where clause. If you only want one object, select one from the list or use FirstOrDefault

user4189129 Over a year ago

Just a tip: I would rethink the way you have implemented your classes. It doesn't make much sense to create a reference to a class which only contains a list. You could make your life a lot easier and move the list to PromotionList

Bassie · Accepted Answer · 2016-12-02 10:17:27Z

1

This part of your code

.Promotion.Find(o=>o.ServiceType.Equals("SAT"));

Returns an AuthenticatePromotion, but you are explicitly asking for a PromotionList object.

One way to get rid of the error would be to use the implicit variable keyword var:

var getPromotion = AuthenticateCustomerResponse.EligiblePromotions.PromotionList.Find(p => p.LineOfBusiness.ToUpper().Equals("VID")).Promotions.Promotion.Find(o=>o.ServiceType.Equals("SAT"));

But then this will of course still return an AuthenticatePromotion

edited Dec 2, 2016 at 10:17

answered Dec 2, 2016 at 10:12

Bassie

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2 Comments

zaria khan Over a year ago

Maybe my query is wrong. Do you think the query is correct to retrieve PromotionList whose LineOfBusiness is equal to "VID" and ServiceType is equal to "SAT ?

Bassie Over a year ago

@zariakhan I think that may depend on the rest of your application, although I must say with such a long line I would recommend placing the entire query into a method with a sensible name to improve readability

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