how to convert list object to list string( getting error Unable to cast object of type)

Question

Hi Friends i have a list of objects private static List<Transaction> transactions;

i am querying through the list to filter the data with some criteria. but i am not able to return the list string. i am getting the error

Unable to cast object of type <>f__AnonymousType1`6[System.Int32,System.String,System.String,System.String,System.String,System.String] to type 'System.String'.

my plan is to make the datagridview source this list like dataGridView2.DataSource = BasicClass.banksearch("ABC");

public static List<string> banksearch(string bankname, string sdate = null, string edate = null, string condition = null)
    {
        List<string> returnstr = new List<string>();
        if (sdate == null && edate == null)//only bank
        {
            returnstr = transactions
                .Where(t => t.BankName == bankname)
                .Select(t => new
                 {
                     TransactionID = t.TransactionID,
                     BankName = t.BankName,
                     TemplateModel = t.TemplateModel,
                     Date = t.Date.ToString(),
                     PayeeName = t.PayeeName,
                     Amount = t.Amount.ToString()
                 }).Cast<String>().ToList();
        }
       return returnstr;
       }

my class file is

class Transaction
{
        public int TransactionID { get; set; }
        public string BankName { get; set; }
        public string TemplateModel { get; set; }
        public DateTime Date { get; set; }
        public string PayeeName { get; set; }
        public decimal Amount { get; set; }        
}

Please give me idea to get the result

You're creating an anonymous object. Why do you expect it to be convertible to a string? I think you may really want to return a List<Transaction> — Yuval Itzchakov
– Yuval Itzchakov, Commented Nov 2, 2014 at 14:47
when i do like this i get error Cannot implicitly convert type 'System.Collections.Generic.List<AnonymousType#3>' to 'System.Collections.Generic.List<chequenew.Transaction>' — Jinesh Sam
– Jinesh Sam, Commented Nov 2, 2014 at 14:59
@JineshSam what do you need to be in these strings you return? — takemyoxygen
– takemyoxygen, Commented Nov 2, 2014 at 15:00
Why not just return transactions.Select(t => t.BankName == bankname).ToList(); ? — takemyoxygen
– takemyoxygen, Commented Nov 2, 2014 at 15:02
@takemyoxygen i am getting this error Error 1 Cannot implicitly convert type 'System.Collections.Generic.List<AnonymousType#1>' to 'System.Collections.Generic.List<string>' — Jinesh Sam
– Jinesh Sam, Commented Nov 2, 2014 at 15:09

Yuval Itzchakov · Accepted Answer · 2014-11-02 15:05:07Z

3

There is no need to project the entire collection onto an Anonymous Object. All you're actually doing is filtering by bankname:

public static List<Transaction> BankSearch(string bankname, string sdate = null, string edate = null, string condition = null)
{
    List<Transaction> filteredTransactions = new List<Transaction>();
    if (sdate == null && edate == null)
    {
        filteredTransactions = transactions.Where(t => t.BankName == bankname).ToList();
    }

    return filteredTransactions;
}

answered Nov 2, 2014 at 15:05

Yuval Itzchakov

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6 Comments

Stephen Kennedy Over a year ago

You don't need to create new List<Transaction>() when your query is calling ToList(). For callers which enter the if block, you are creating a list twice.

Yuval Itzchakov Over a year ago

Enumerable.Where returns an IEnumerable<Transaction>, not a List<Transaction>. That's why i call ToList.

Jinesh Sam Over a year ago

@Yuval Itzchakov Now no error but no items to display in the datagridview

Yuval Itzchakov Over a year ago

@JineshSam That may be because your DataGridView doesn't know how to represent a custom object.

Yuval Itzchakov Over a year ago

@StephenKennedy I understand, but i think that isn't the point of the question.

|

Stephen Kennedy · Accepted Answer · 2014-11-02 15:16:13Z

1

You don't need to convert to a string in order to use this result as a datasource (although if you actually need a string I can show you how to create a formatted string instead of an anonymous class object). You likely need something like this:

public static List<Transaction> banksearch(string bankname, string sdate = null, string edate = null, string condition = null)
    {
        if (sdate == null && edate == null)//only bank
        {
           return transactions // type: List<Transaction>
                .Where(t => t.BankName == bankname)
                .ToList();
        } else {
           return new List<Transaction>();
       }
  }

edited Nov 2, 2014 at 15:16

answered Nov 2, 2014 at 15:09

Stephen Kennedy

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9 Comments

Yuval Itzchakov Over a year ago

There's no need to project a new Transaction for each object. transcations is already a List<Transaction>.

Stephen Kennedy Over a year ago

I'm not. That's the else block effectively.

Yuval Itzchakov Over a year ago

Sorry, i didn't understand your comment. what else block?

Stephen Kennedy Over a year ago

Inside the if, I return query.ToList(). Method execution ends at that point. Callers which didn't hit the if will hit return new List<Transaction>();. I've made this explicit now by adding an else block.

Yuval Itzchakov Over a year ago

Im not talking about that. Your LINQ query generated a new Transcation for each transaction object. It's unnecessary as the source collection is already a List<Transaction>. See my answer.

|

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