How can I return a value inside Select() Lambda Expression

Question

See the following example, now I need to check if UserService.GetByUserID() is null then return String.Empty. How can I still do this in one line?

var benefits = customerBenefits.Select(n =>
    new CustomerBenefit(n.BenefitID,
        n.AddedByUserID.HasValue 
            ? UserService.GetByUserID(n.AddedByUserID.Value).DisplayName 
            : n.AddedByAgentID, n.Reason);

Where do you want to return an empty string? It would be very odd to return either an empty string or a CustomerBenefit. Do you mean you need it for one of the constructor arguments? It would really help if you'd give more information. — Jon Skeet
– Jon Skeet, Commented Jun 24, 2014 at 6:27
I need to add another condition to check if the GetByUserID() return null then return emptystring else return DisplayName — OKEEngine
– OKEEngine, Commented Jun 24, 2014 at 6:30
And do you really want to use AddedByAgentId instead of a display name if there isn't an AddedByUserId? Don't you want to look up the agent's display name? — Jon Skeet
– Jon Skeet, Commented Jun 24, 2014 at 6:37

Petar Vučetin · Accepted Answer · 2014-06-24 06:39:34Z

5

Call service first then assign result.

var benefits = customerBenefits
                        .Select(n => {
                            var user = serService.GetByUserID(n.AddedByUserID.Value);

                            return new CustomerBenefit(
                                n.BenefitID,                   
                                n.AddedByUserID.HasValue ? (user== null ? String.Empty : ).DisplayName) : n.AddedByAgentID,
                                n.Reason} );

answered Jun 24, 2014 at 6:39

Petar Vučetin

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Comments

Me.Name · Accepted Answer · 2014-06-24 06:45:21Z

2

By using let in query syntax, you can store sub results:

var benefits = from n in customerBenefits
    let hasuserid = n.AddedByUserID.HasValue
    let user = hasuserid ? UserService.GetByUserID(n.AddedByUserID.Value) : null //the call to GetUserID is stored here
           select
                new CustomerBenefit(
                    n.BenefitID,                   
                    hasuserid 
                         ? (user == null ? string.Empty : user.DisplayName) //the stored sub result is reused
                         : n.AddedByAgentID,
                    n.Reason);

edited Jun 24, 2014 at 6:45

answered Jun 24, 2014 at 6:36

Me.Name

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Comments

Akram Shahda · Accepted Answer · 2014-06-24 06:44:30Z

0

You can try something like that:

var benefits = customerBenefits.Select(n =>
        new CustomerBenefit(
            n.BenefitID,                   
            n.AddedByUserID.HasValue 
                ? (UserService.GetByUserID(n.AddedByUserID.Value) == null 
                    ? String.Empty 
                    : UserService.GetByUserID(n.AddedByUserID.Value).
                        DisplayName) 
            : n.AddedByAgentID,
            n.Reason);

edited Jun 24, 2014 at 6:44

Akram Shahda

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answered Jun 24, 2014 at 6:30

Shaiba7

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1 Comment

OKEEngine Over a year ago

I know but GetByUserID() gets called twice.

Karthik AMR · Accepted Answer · 2014-06-24 06:48:24Z

0

Is this what you need?

var benefits = from n in customerBenefits
    let id = n.AddedByUserID.HasValue
    let user = id ? UserService.GetByUserID(n.AddedByUserID.Value) : null            select
                new CustomerBenefit(
                    n.BenefitID,                   
                    id ? (user == null ? string.Empty : user.DisplayName)
                         : n.AddedByAgentID,
                    n.Reason);

edited Jun 24, 2014 at 6:48

answered Jun 24, 2014 at 6:32

Karthik AMR

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1 Comment

OKEEngine Over a year ago

It is what I want to do but I don't want GetByUserID() to be called twice.

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