Where condition using Linq

Question

I have a table in the database as

Code            No                 Email            Pwd
-----------------------------------------------------------    
ABCDEFG         1             aaa@gmail.com          1
EYETW           2             bbb@gmail.com          2
WDHH0           3                  NULL             NULL
DZDX220         4                  NULL             NULL
AL7F0MI         5                  NULL             NULL
Q5D6M4R         6                  NULL             NULL

Now, in this table I have to check if the email used by the user already exists then I want to retrieve the row, if the email doesn't exist then I have to check if the Pwd has been already used and retrieve the row data.

I have tried this

var data = (from table in ds.Tables[0].AsEnumerable()
            where table.Field<Int16>("Pwd") == Convert.ToInt16(pwd) || table.Field<string>("Email") != email
            select new {emailAddress = table.Field<string>("email") , passsword = table.Field<Int16>("Pwd") }).FirstOrDefault();

But it is not returning the right answers.

Test cases :

If I pass aaa@gmail.com and 2 then I have to retrieve `aaa@gmail.com 1 .

If I pass bbb@gmail.com and 1 then I want to retrieve bbb@gmail.com 2 or null .

Sorry guys, if any of them exist, I want to retrieve those values but not nulls

Answer 1

You need to update your Where(). It should be like:

var data = (from table in ds.Tables[0].AsEnumerable()
            where (table.Field<string>("Email") == email) //email exists
            || (table.Field<string>("Email") != email && table.Field<Int16>("Pwd") == Convert.ToInt16(pwd)) //email doesn't exist, but password does
            select new {emailAddress = table.Field<string>("email") , passsword = table.Field<Int16>("Pwd") }).FirstOrDefault();

Answer 2

As Yacoub pointed in the comment, issue is with table.Field<string>("Email") == email it should be == email .

var matchingrow = ds.Tables[0].AsEnumerable()
                              .FirstOrDefault(table=> table.Field<Int16>("Pwd") == Convert.ToInt16(pwd) 
                                                   || table.Field<string>("Email") == email);

if(matchingrow != null)
{
    // matching email/pwd. logic goes here

    // matchingrow.Field<string>("Email");
}