LINQ Select within List of custom type?

Question

I'm using SparkPost on my application to send emails to me and clients. In order to do this, I need to serialize an array using C#. I have the following code that does not seem to be working and I have no idea why.

recipients = new List<Recipient>() {
    toAddresses.Select(addr => new Recipient() {
        address = addr.ToString()
    })
}

toAddresses is just a List<string> with email addresses.

Recipient class:

class Recipient {
    public string address;
}

The output of that LINQ select should look like this:

recipients = new List<Recipient>(){
    new Recipient() {
        address ="[email protected]"
    },
    new Recipient() {
        address ="[email protected]"
    },
    new Recipient() {
        address ="[email protected]"
    },
    new Recipient() {
        address ="[email protected]"
    }
}

Any help would be great, thanks!

Specific Errors:

Error CS1503 Argument 1: cannot convert from 'System.Collections.Generic.IEnumerable' to 'app.Recipient'

Error CS1950 The best overloaded Add method 'List.Add(Recipient)' for the collection initializer has some invalid arguments

Request String:

wc.UploadString("https://api.sparkpost.com/api/v1/transmissions", JsonConvert.SerializeObject(
new {
    options = new {
        ip_pool = "sa_shared"
    },
    content = new {
        from = new {
            name = "a Sports",
            email = "[email protected]"
        },
        subject = subject,
        html = emailBody
    },
    recipients = new List<Recipient>() {
        toAddresses.Select(addr => new Recipient() {
            address => addr
        })
    }
}

));

Can you please describe in what way your current code "does not seem to be working?" Are you getting an error message? Different output than you'd expected? — StriplingWarrior
– StriplingWarrior, Commented Apr 17, 2017 at 14:54

Fabio · Accepted Answer · 2017-04-17 15:17:15Z

7

Seems like you need simple mapping

var recipients = toAddresses.Select(addr => new Recipient { address = addr }).ToList();

You cannot use IEnumerable as parameter for list initialization

var recipients = new List<Recipient>() { toAddresses.Select...  }

Initialization logic will call List.Add on every item you pass in { }, so it expects instances of Recepient separated by comma, but when you pass there IEnumerable it fail.

List<T> have overload constructor which accept IEnumerable<T> as argument so you can use this

var recepients = new List<Recepient>(toAddresses.Select(addr => new Recipient {address = addr}));

But on my own opinion simple mapping seems more readable.

var message = new 
{
    options = new 
    { 
        ip_pool = "sa_shared"
    },
    content = new 
    {
        from = new 
        {
            name = "a Sports",
            email = "[email protected]"
        },
        subject = subject,
        html = emailBody
    },
    recipients = toAddresses.Select(addr => new Recipient() { address = addr}).ToList()
}

edited Apr 17, 2017 at 15:17

answered Apr 17, 2017 at 14:50

Fabio

32.5k4 gold badges35 silver badges77 bronze badges

Sign up to request clarification or add additional context in comments.

9 Comments

StriplingWarrior Over a year ago

Why would this work when his existing code doesn't work?

willeM_ Van Onsem Over a year ago

@StriplingWarrior: because when the List<Recipient> constructor is invoked, the compiler expects the LINQ query to result in a single recipient. It gives an error: Argument #1' cannot convert System.Collections.Generic.IEnumerable<Recipient>' expression to type Recipient'`.

juharr Over a year ago

@WillemVanOnsem I think the point was that the reason should be part of the answer.

StriplingWarrior Over a year ago

Good edit. You may also want to mention that he could have passed the Select result into the constructor of the new List<Recipient().

StriplingWarrior Over a year ago

@AndriiLitvinov: I only said that because I think that's what the OP probably thought he was doing. The fact that he was newing up a List and trying to pass values through the initializer makes me think he'd seen a similar approach before (using the constructor argument) and was just getting confused between the two syntaxes. Fabio did a great job with this answer.

|

Collectives™ on Stack Overflow

LINQ Select within List of custom type?

1 Answer 1

9 Comments

Your Answer

Hot Network Questions

Collectives™ on Stack Overflow

1 Answer 1

9 Comments

Your Answer

Sign up or log in

Post as a guest

Related