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how to query datatable using linq?

Posted on 2011-03-12

1 solution

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Last Modified: 2013-12-17

hi,

I have datatable, and I wanna query specific customer record from datatable using his id by linq,

so how can I do that using linq?

while I was trying, I got null value selected as return !, here is my code snippet:

private Customer GetCustomerInfo(string id)
        {
            Customer cm = null;
            var customers = (from customer in dtCustomers.AsEnumerable()
                         //where customer.Field<string>("id") == id
                         select new { 
                             CustomerId = customer["id"],
                             CustomerEnName = customer["EnName"],
                             CustomerArName = customer["ArName"],
                             CustomerClass = customer["EnClass"],
                             CustomerCellPhone = customer["CellPhone"],
                             Telephone = customer["Telephone"],
                             CustomerEmail = customer["Email"],
                             CustomerIsActive = customer["Active"],
                             CustomerNationalId = customer["NationalId"],
                             CustomerNationalIdType = customer["NationalIdType"]
                         }).Take(1);

            foreach (var c in customers)//I got customers always null even the id is correct
            {
                cm = new Customer(c.CustomerId.ToString(), "LMR-" + Other.changeTo6Digits(c.CustomerId.ToString()), c.CustomerEnName.ToString(), c.CustomerArName.ToString(), "", c.CustomerCellPhone.ToString(), c.Telephone.ToString(), c.CustomerEmail.ToString(), c.CustomerClass.ToString(), c.CustomerIsActive.ToString(), "", c.CustomerNationalId.ToString(), c.CustomerNationalIdType.ToString());
                break;
            }
            return cm;

        }

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private Customer GetCustomerInfo(string id)
        {
            Customer cm = null;
            var customers = (from customer in dtCustomers.AsEnumerable()
                         //where customer.Field<string>("id") == id
                         select new { 
                             CustomerId = customer["id"],
                             CustomerEnName = customer["EnName"],
                             CustomerArName = customer["ArName"],
                             CustomerClass = customer["EnClass"],
                             CustomerCellPhone = customer["CellPhone"],
                             Telephone = customer["Telephone"],
                             CustomerEmail = customer["Email"],
                             CustomerIsActive = customer["Active"],
                             CustomerNationalId = customer["NationalId"],
                             CustomerNationalIdType = customer["NationalIdType"]
                         }).Take(1);

            foreach (var c in customers)//I got customers always null even the id is correct
            {
                cm = new Customer(c.CustomerId.ToString(), "LMR-" + Other.changeTo6Digits(c.CustomerId.ToString()), c.CustomerEnName.ToString(), c.CustomerArName.ToString(), "", c.CustomerCellPhone.ToString(), c.Telephone.ToString(), c.CustomerEmail.ToString(), c.CustomerClass.ToString(), c.CustomerIsActive.ToString(), "", c.CustomerNationalId.ToString(), c.CustomerNationalIdType.ToString());
                break;
            }
            return cm;

        }

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Comment

Question by:njgroup

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6 Comments

LVL 18

Expert Comment

by:Gary Davis

ID: 351159202011-03-12

Seems like you want to have the DataTable Rows collection as enumerable, not the DataTable itself.

Gary Davis

LVL 64

Accepted Solution

by:Fernando Soto

Fernando Soto earned 2000 total points

ID: 351161912011-03-12

Hi njgroup;

A couple of things your query returns a Anonymous type and NOT a Customer. We know this because in your select clause you have this, select new {, which does not name the type to create and so an Anonymous type is created. Note in the code snippet I have changed that to this, new DtCustomer {, which states to create the new objects of type DtCustomer, the class I also added to the code snippet. An Anonymous type really has no use outside of the method that created it therfore the reason for creating a concrete type DtCustomer to return to the caller. I also changed the Take(1) to FirstOrDefault(). The Take() method returns, "If count is less than or equal to zero, source is not enumerated and an empty IEnumerable(Of T) is returned.", where the FirstOrDefault returns a null if no result was found, better for error checking.

private DtCustomer GetCustomerInfo(string id)
{
    var customer  = (from customer in dtCustomers.AsEnumerable()
                     where customer.Field<string>("id") == id
                     select new DtCustomer { 
                         CustomerId = customer.Field<int>("id"),
                         CustomerEnName = customer.Field<string>("EnName"),
                         CustomerArName = customer.Field<string>("ArName"),
                         CustomerClass = customer.Field<string>("EnClass"),
                         CustomerCellPhone = customer.Field<string>("CellPhone"),
                         Telephone = customer.Field<string>("Telephone"),
                         CustomerEmail = customer.Field<string>("Email"),
                         CustomerIsActive = customer.Field<string>("Active"),
                         CustomerNationalId = customer.Field<int>("NationalId"),
                         CustomerNationalIdType = customer.Field<string>("NationalIdType")
                     }).FirstOrDefault();

    return customer;
}

public class DtCustomer
{
    public int CustomerId {get; set;}    
    public string CustomerEnName {get; set;}    
    public string CustomerArName {get; set;}    
    public string CustomerClass {get; set;}    
    public string CustomerCellPhone {get; set;}    
    public string Telephone {get; set;}
    public string CustomerEmail {get; set;}
    public string CustomerIsActive {get; set;}
    public int CustomerNationalId {get; set;}
    public string CustomerNationalIdType {get; set;} 
}

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Fernando

Author Comment

by:njgroup

ID: 351199032011-03-12

thanks very much, but I get an strange error on where statement

Unable to cast object of type 'System.Int32' to type 'System.String'.

even I have it as sting but I dont know really why it give variable as integer!

private Customer GetCustomerInfo(string id)
        {
            var customer1 = (from customer in dtCustomers.AsEnumerable()
                            where customer.Field<string>("id") == id // <-- exception generated here
                            select new Customer
                            {
                                id = customer.Field<string>("id"),
                                enName = customer.Field<string>("EnName"),
                                arName = customer.Field<string>("ArName"),
                                type = customer.Field<string>("EnClass"),
                                cellPhone = customer.Field<string>("CellPhone"),
                                tel = customer.Field<string>("Telephone"),
                                email = customer.Field<string>("Email"),
                                isActive = customer.Field<string>("Active"),
                                nationalId = customer.Field<string>("NationalId"),
                                nationalIdType = customer.Field<string>("NationalIdType")
                            }).FirstOrDefault();

            return customer1;
        }

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Author Comment

by:njgroup

ID: 351199342011-03-12

Ok, I solve the problem :D thanks very much

Author Closing Comment

by:njgroup

ID: 351199362011-03-12

solution is perfect

LVL 64

Expert Comment

by:Fernando Soto

ID: 351214632011-03-13

Not a problem, glad I was able to help. ;=)

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