Convert an array of integers for use in a SQL “IN” clause

Question

Surely there is a framework method that given an array of integers, strings etc converts them into a list that can be used in a SQL \"IN\" clause?

e.g.

Answer 1

If your list of integers is large, you may end up generating a string that is too long for your database to accept. E.g. I think the maximum length of a VARCHAR in SQL2000 is around 8K.

So I have a set of helper method something like the sample below, which return an enumeration of strings, which can then be used as follows:

List idList = ...;
using(SqlCommand command = ...)
{
    ...
    foreach(string idString in ConcatenateValues(ids,",", maxLength, false))
    {
       command.Parameters[...] = idString;
       // or command.CommandText = "SELECT ... IN (" + idString + ")...";
       ... execute command ...
    }
}

The concatenate method might look something like the following:

public static IEnumerable ConcatenateValues(IEnumerable values, string separator, int maxLength, bool skipDuplicates)
{
    IDictionary valueDictionary = null;
    StringBuilder sb = new StringBuilder();
    if (skipDuplicates)
    {
        valueDictionary = new Dictionary();
    }
    foreach (int value in values)
    {
        if (skipDuplicates)
        {
            if (valueDictionary.ContainsKey(value)) continue;
            valueDictionary.Add(value, "");
        }
        string s = value.ToString(CultureInfo.InvariantCulture);
        if ((sb.Length + separator.Length + s.Length) > maxLength)
        {
            // Max length reached, yield the result and start again
            if (sb.Length > 0) yield return sb.ToString();
            sb.Length = 0;
        }
        if (sb.Length > 0) sb.Append(separator);
        sb.Append(s);
    }
    // Yield whatever's left over
    if (sb.Length > 0) yield return sb.ToString();
}