How do I access Dictionary items?

Question

I am developing a C# VS2008 / SQL Server website app and am new to the Dictionary class. Can you please advise on best method of accomplishing this? Here is a code snippet:

SqlConnection conn2 = new SqlConnection(connString);
SqlCommand cmd = conn2.CreateCommand();
cmd.CommandText = "dbo.AppendDataCT";
cmd.CommandType = CommandType.StoredProcedure;
cmd.Connection = conn2;
SqlParameter p1, p2, p3;
foreach (string s in dt.Rows[1].ItemArray)
{
    DataRow dr = dt.Rows[1]; // second row
    p1 = cmd.Parameters.AddWithValue((string)dic[0], (string)dr[0]);
    p1.SqlDbType = SqlDbType.VarChar;
    p2 = cmd.Parameters.AddWithValue((string)dic[1], (string)dr[1]);
    p2.SqlDbType = SqlDbType.VarChar;
    p3 = cmd.Parameters.AddWithValue((string)dic[2], (string)dr[2]);
    p3.SqlDbType = SqlDbType.VarChar;
}

but this is giving me compiler error:

The best overloaded method match for 'System.Collections.Generic.Dictionary<string,string>.this[string]' has some invalid arguments

I just want to access each value from "dic" and load into these SQL parameters. How do I do this? Do I have to enter the key? The keys are named "col1", "col2", etc., so not the most user-friendly. Any other tips? Thanks!

Answer 1

You seem to be trying to access a Dictionary<string, string> by integer index. You can't do that - you have to look up the value by the key, which is a string.

If you don't want to use string keys, why are you using a Dictionary<string, string> to start with? Could you either use a List<string> or a Dictionary<int, string>?

Note that once you have managed to use the indexer appropriately, you won't need to cast to string.

Answer 2

Yes values must be accessed by the key.

Answer 3

A Dictionary maps objects of one type into objects of another type. In your case you've got a Dictionary<string, string>. So if you had it initialised like this:

Dictionary<string, string> dic = new Dictionary<string, string>()
{
   { "key1", "value1" },
   { "key2", "value2" },
   { "key3", "value3" }
};

You'd get the value for key2 by doing

dic["key2"]; // gives "value2"

The Dictionary is strongly-typed, so there's no need for any casting. As Jon Skeet says, you may be better off with a List<string> here. You can access these by the integer index.

Answer 4

If your keys are "col1", "col2", etc then using 0, 1, etc will cause the error you're getting. Try this:

p1 = cmd.Parameters.AddWithValue(dic["col1"], dr[0]);
p1.SqlDbType = SqlDbType.VarChar;
p2 = cmd.Parameters.AddWithValue(dic["col2"], dr[1]);
p2.SqlDbType = SqlDbType.VarChar;
p3 = cmd.Parameters.AddWithValue(dic["col3"], dr[2]);
p3.SqlDbType = SqlDbType.VarChar;

Also, there is no need to cast to string as the dictionary object will return strings already.

Answer 5

I can't understand what really you are looking for, so here is my small advice. There is a way to browse dictionary by not requesting items by key. It's a foreach option.

foreach (KeyValuePair<string,string> pair in dic)
{
    p. = cmd.Parameters.AddWithValue(dic.Value /*or dic.Key*/, (string)dr[0]);
    p.SqlDbType = SqlDbType.VarChar;
    // further processing of this parameter
}

Answer 6

Here's a piece of code that will do what you're after, I think.. You will have to add in an else statement, but it should get you started.

public void AttachParam(ref DbCommand command, Dictionary<string, string> parameters)
{
  try
  {
     if (parameters.Count > 0)
     {
        foreach (KeyValuePair<string, string> kvp in parameters)
        {
           command.Parameters.AddWithValue(kvp.Key, kvp.Value);
        }
     }
  }
  catch (Exception ex)
  {
     throw;
  }
}