How do I re-generate a random string if generated string already exists the database

Question

0.00/5 (No votes)

See more:

I think i have a simple situation which i can't seem to solve and i'm hoping someone would shed some light on this:

basically i have a method that is generating a random number like this:

p

C#

Public static string Code()
            {
                var characters = "ABCDEFGHIJKLMNOPQRSTUVWXYZ0123456789";
                var c= new char[6];
                var random = new Random();
    
                for (int i = 0; i < c.Length; i++)
                {
                    c[i] = characters[random.Next(characters.Length)];
                }
    
                var code = new String(c);
                return code;
            }

I have another method that is checking if the generated code in the method above already exists in the database. If the code exists then re - generate another code .

C#

public void SetCode()
        {

           string _code = Code();
            using(var db = new Database())
                    {
                        var p = db.Codes.Where(pc => pc.Code.Equals(Code));

                        
                        if (p.Any())
                        {
                          // this is where i'm stuck, if the code exist i'll do i send it back to generate another code?
                        }
                      //if code doesn't exist in the db save it....
                    }
                   
        }

How can I go ahead and achieve this?
Thank you

What I have tried:

Looked at do while loops and

C#

if (p.Any())
                        {
                          // this is where i'm stuck, if the code exist i'll do i send it back to generate another code?
                        }
                      //if code doesn't exist in the db save it....
                    }
                   
        }

Posted 25-Aug-17 0:21am

1Future

Updated 29-Aug-17 1:38am

Add a Solution

Comments

Thanks7872 25-Aug-17 6:59am

Which database is there?

BillWoodruff 25-Aug-17 10:02am

Do you know how to write to a Database ? How to change an existing value in a Database ? Unless you know how, with your current Database, to Create, Read, Update and Delete (CRUD), you will not make progress.

You need to review your Database documentation.

Richard Deeming 25-Aug-17 12:47pm

Either a while[^] or a do..while[^] will do the trick. What's the problem?

string code;
using (var db = new Database())
{
    do
    {
        code = Code();
    }
    while (db.Codes.Any(pc => pc.Code == code))
}

string code = Code();
using (var db = new Database())
{
    while (db.Codes.Any(pc => pc.Code == code))
    {
        code = Code();
    }
}

BillWoodruff 25-Aug-17 15:17pm

I'd be voting #5 for this if posted as solution.

3 solutions

Solution 2

Solution A:
1) Set a unique constraint on that field in the table
2) Check for insert failure
3) regenerate upon failure.

Solution B:
1) Generate random string
2) use query to check for it in field
3) regenerate if it exists

For A and B
4) Repeat as necessary, but, if your random strings are short, I'd possibly limit retries in case your table gets too densely populated and it runs 'forever'-ish.

Solution A will, overall, require fewer table queries. Also, it prevents other users who were less careful from screwing up the columns uniqueness because the constraint is always in effect.

Posted 25-Aug-17 0:39am

W∴ Balboos, GHB

Comments

1Future 25-Aug-17 6:43am

Hi thanks for the response .. I think solution B is what i'm trying to achieve in the code above . but, i'm stuck on how i can regenereate if code still exists .. maybe this is where can show me in code example?

W∴ Balboos, GHB 25-Aug-17 6:50am

You marked this as a C# question so I would expect you to be familiar with C#'s conditional loops. Use a loop - break with success (like uid/pwd input would do in a login).

With 26^6 possible combinations, unless they're rapidly machine generated for some kind of test, this will not happen very often. There's nearly 40 billion unique combinations.

An additional hint: if you use Solution B, in particular, I'd put an index on that field if it's going to start to fill up.

Dave Kreskowiak 25-Aug-17 8:57am

It's 36^6 and it's only 2.176 billion combinations. :)

Dave Kreskowiak 25-Aug-17 8:54am

Option A is the only one that is feasible.

Option B has the problem of checking for it then doing the insert in a separate operation. Well, what if, during the check, it doesn't exist, but during the insert it suddenly does because of multiple users? Now you have to handle the case where the check is good but the insert fails. Sure you could get around this with carefully crafted SQL, but given the skill level of the OP, ...

Solution 1

If you must use randomized strings, then the solution that I would recommend is:

C#

var random = Guid.NewGuid().ToString("N");

Posted 25-Aug-17 0:32am

Graeme_Grant

Comments

1Future 25-Aug-17 6:34am

How do I sepecify how many characters?? ... I Would like 6 characters in length

Graeme_Grant 25-Aug-17 6:37am

6 characters? maybe base32 encoding might get you there: Base32 Encoder and Decoder in C#[^] but you would be better off increasing the size of the field just incase encoding causes dupelicates.

Add a Solution

Add your solution here

Treat my content as plain text, not as HTML

Preview 0

…

Existing Members

Sign in to your account

...or Join us

Download, Vote, Comment, Publish.

Your Email
Password
Forgot your password?

Your Email
This email is in use. Do you need your password?
Optional Password

I have read and agree to the Terms of Service and Privacy Policy
Please subscribe me to the CodeProject newsletters

When answering a question please:

Read the question carefully.
Understand that English isn't everyone's first language so be lenient of bad spelling and grammar.
If a question is poorly phrased then either ask for clarification, ignore it, or edit the question and fix the problem. Insults are not welcome.
Don't tell someone to read the manual. Chances are they have and don't get it. Provide an answer or move on to the next question.

Let's work to help developers, not make them feel stupid.

This content, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Richard Deeming · Accepted Answer · 2017-08-29T01:37:00

As I mentioned in the comments, either a while[^] or a do..while[^] will do the trick.

string code;
using (var db = new Database())
{
    do
    {
        code = Code();
    }
    while (db.Codes.Any(pc => pc.Code == code))
}

string code = Code();
using (var db = new Database())
{
    while (db.Codes.Any(pc => pc.Code == code))
    {
        code = Code();
    }
}

How do I re-generate a random string if generated string already exists the database

3 solutions

Solution 2

Solution 1

Solution 3

Add your solution here

Preview 0

Existing Members

...or Join us