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

C# how to populate list of lists

1 Answers1