C# how to populate list of lists

Question

I am attempting to create a class of lists

 public class comparisonData
{
    public List<string> Tables { get; set; }
    public List<string> Constraints { get; set; }
    public List<string> StoredProcs { get; set; }
    public List<string> Views { get; set; }
    public List<string> Functions { get; set; }
    public List<string> Columns { get; set; }
    public List<string> Synonyms { get; set; }
    public List<string> NotNullables { get; set; }


}

And then instantiate said class as a list

List<comparisonData> cList = new List<comparisonData>();

My end goal is to have a list of several different database names which each have Lists that contain said databases table names, columns, constraints etc.

However I am receiving an "Index was out of range. Must be non-negative and less than the size of the collection" error when I try to populate my lists

        while(reader.Read())
        {
            cList[0].Tables.Add(reader.GetString(0));
        }

Am I instantiating something wrong? Or is this list of lists just bad code and I should pursue a different mean to my end goal?

You have a zero-length List. You should add at least one item to be able to use `cList[0]` — L.B, Jun 09 '14 at 17:19
Can you include call stack in your question? I guess `GetString(0)` call is the problem, not list itself. — MarcinJuraszek, Jun 09 '14 at 17:19
When do you allocate the List for the elements of comparisonData class? — roscoe_casita, Jun 09 '14 at 17:20
Please checkout FAQ on the exception - http://stackoverflow.com/questions/20940979/what-is-indexoutofrangeexception-and-how-do-i-fix-it/20940980#20940980 — Alexei Levenkov, Jun 09 '14 at 17:27

Felipe Oriani · Accepted Answer · 2014-06-09T17:45:58.517

First, name your class with appropriate code and on the constructor, instance the collections, for sample:

public class ComparisonData
{
    public List<string> Tables { get; set; }
    public List<string> Constraints { get; set; }
    public List<string> StoredProcs { get; set; }
    public List<string> Views { get; set; }
    public List<string> Functions { get; set; }
    public List<string> Columns { get; set; }
    public List<string> Synonyms { get; set; }
    public List<string> NotNullables { get; set; }

    public ComparisonData()
    {
        Tables = new List<string>();
        Constraints = new List<string>();
        // other properties...
    }
}

And in the loop, just create a object from ComparisonData and set some values on the properties lists , for sample:

List<ComparisonData> cList = new List<ComparisonData>();

while(reader.Read())
{
   ComparisonData c = new ComparisonData();

   c.Tables.Add(reader.GetString(0));
   // other properties

   // since it is a List, just call the Add method and pass the object
   cList.Add(c);
}

You'll get a NRE when adding items to those uninitialized sub-lists. — Servy, Jun 09 '14 at 17:34
Thankyou! This solved my issue should have realized I needed to instantiate my inner lists — user3723223, Jun 09 '14 at 17:36
@user3723223: You are welcome. Also, since you are new to StackOverflow, I would like to inform you that you can upvote good answers and accept the answer that helped you the most by checking the tick mark next to the Answer. On this site an upvote or an accepted answer counts as a "thanks". — Olivier Jacot-Descombes, Jun 09 '14 at 17:54

C# how to populate list of lists

1 Answers1