string to varchar C# / SQL Server

Question

I have an application where I need to store a value in a column. The value is a string in the code and the column data type is nvarchar.

foreach (DataRow row in dt.Rows)
{
    //Generate a random length for randomKey range between 3 and 6 characters
    Random randKey = new Random();
    int randKeyLength = randKey.Next(3, 6);

    //calculate randomKeyString
    String randomKeyString = md5Prepare.gen_randomKeyString(randKeyLength);

    //add randomKeyString to database
    row["randomKey"] = randomKeyString;
}

When I check the database, the column "randomKey" is unchanged. What is wrong here?

When I check the database, the column "randomKey" - I see no code for update in database, how are you updating the database ? — Habib
– Habib, Commented Nov 28, 2012 at 6:42
You're just updating the DataRow in your DataTable (all in-memory representations of your data) - you're not yet storing it back to the database! — marc_s
– marc_s, Commented Nov 28, 2012 at 6:42
Doesn't row["randomKey"] = randomKeyString; change the column value for that specific row? — coffeeak
– coffeeak, Commented Nov 28, 2012 at 6:42
It changes the value for that column in that DataRow - in memory (RAM) - but NOT in the database table. Check out something like this basic ADO.NET tutorial to study the basics of accessing a database using "raw" ADO.NET — marc_s
– marc_s, Commented Nov 28, 2012 at 6:43

VMAtm · Accepted Answer · 2012-11-28 06:48:37Z

1

You didn't call any Commit methods on DataRow or DataTable.
You need the DataAdapter and DataSet to actually update database.

foreach (...)
{
    // your code here
}
DataSet dataSet = new DataSet();
dataSet.Tables.Add(dt);
SqlDataAdapter adapter = new SqlDataAdapter();
adapter.Update(dataSet);

answered Nov 28, 2012 at 6:48

VMAtm

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5 Comments

coffeeak Over a year ago

Your solution gives the following error: Update unable to find TableMapping['Table'] or DataTable 'Table'.

VMAtm Over a year ago

@user1109363 Well, it is up to you to create DataAdapter in your connection, and call him right way.

coffeeak Over a year ago

I am sorry, I don't quite understand.

VMAtm Over a year ago

@user1109363 read the tutorial marc_s mentioned. After that - use methods for your own database.

VMAtm Over a year ago

@user1109363 Good luck with your projects :)

Tyler Durden · Accepted Answer · 2012-11-28 06:46:06Z

0

There is nothing wrong with what you are doing to set the value. Strings are unicode in C# as is nvarchar. You simply need to write the values back/insert them into the database as what you are doing at the moment is manipulating the in memory representations of what you have read from the database.

answered Nov 28, 2012 at 6:46

Tyler Durden

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Comments

callisto · Accepted Answer · 2012-11-28 06:46:16Z

0

Do not create the instance of the Random object inside the foreach: Rather create it before.

The sequence of random numbers generated by a single Random instance is supposed to be uniformly distributed. By creating a new Random instance for every random number in quick successions, you are likely to seed them with identical values and have them generate identical random numbers. Of course, in this case, the generated sequence will be far from uniform distribution.

For the sake of completeness, if you really need to reseed a Random, you'll create a new instance of Random with the new seed:

rnd = new Random(newSeed);

Thanks to Mehrdad Afshari

answered Nov 28, 2012 at 6:46

callisto

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