CODEWITHSUNDEEP
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user2939293
user2939293

Reputation: 813

How to search through List<string>?

I have database with table tbl_employee. In the table I store usernames. I use the following code to save all the usernames into a List:

string name = txtUsername.Text;       
List<string> lst = new List<string>();

NpgsqlConnection conn = new NpgsqlConnection("Server=127.0.0.1;Port=5432;Database=db;User Id=postgres;Password=postgres;"); 

conn.Open();
string sql = "SELECT username FROM tbl_employee";
NpgsqlCommand command = new NpgsqlCommand(sql, conn);  
NpgsqlDataReader dr = command.ExecuteReader();  
while (dr.Read())
{
    lst.Add(dr.GetString(0));
}

Now, my question is how can I search through my list (lst) to see if the users input from textbox (name) exists in the list?

I have tried this:

if (lst.FindString(name)) 
    //Says it has some invalid arguments

And this:

if (lst.Exists(element => element == name)) 
    //It says name exists even though it doesn't

Upvotes: 0

Views: 168

Answers (3)

user2939293
user2939293

Reputation: 813

Thanks quys! I changed it to count, as you suggested. Here is my final code:

string name = txtUsername.Text;       

NpgsqlConnection conn = new NpgsqlConnection("Server=127.0.0.1;Port=5432;Database=db;User Id=postgres;Password=postgres;"); 

conn.Open();
string sql = "SELECT COUNT(*) FROM tbl_employee WHERE username = @val1";
NpgsqlCommand command = new NpgsqlCommand(sql, conn);  
command.Parameters.AddWithValue("@val1", name);
var result = command.ExecuteScalar();
int i = Convert.ToInt32(result);
if (i != 0)
{
    FormsAuthentication.RedirectFromLoginPage(name, Persist.Checked);
}
else
{
    lblMessage.Text = "Invalid username or password";
 }

Upvotes: 1

p.s.w.g
p.s.w.g

Reputation: 149078

You could just use Contains:

if (lst.Contains(name)) ...

But if this is all you're doing with the list, I'd recommend changing this code so it queries the tbl_empoyee table directly from the database. I'm not familiar with the NpgsqlCommand but it should look a bit like this:

bool result = false;
string sql = "SELECT username FROM tbl_employee WHERE username = :name";
NpgsqlCommand command = new NpgsqlCommand(sql, conn);  
command.Parameters.AddWithValue("name", name);
NpgsqlDataReader dr = command.ExecuteReader();  
while (dr.Read())
{
    result = true; // record found
}

Or like this (following Tim Schmelter's suggestion):

string sql = "SELECT COUNT(*) FROM tbl_employee WHERE username = :name";
NpgsqlCommand command = new NpgsqlCommand(sql, conn);  
command.Parameters.AddWithValue("name", name);
int found = (int)command.ExecuteScalar();  // 1 = found; 0 = not found

Upvotes: 3

eddie_cat
eddie_cat

Reputation: 2593

Try using lst.Contains(name).

Upvotes: 2

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