Returning List<int> from Database [closed]

Question

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Closed 8 years ago.

I have a simple problem that I have not been able to find an answer to despite much Googling. Perhaps posting this question up will help the next poor soul who looks for the same answer.

I have a query that returns a collection of distinct ID's.

I am creating an SQLCommand with this query and using ExecuteScalar( ) to run it.

ExecuteScalar( ) appears to return an object and will not allow me to cast it to List.

What is the best practice to fix this and how can I fix this problem?

Answer 1

execute scalar returns a single piece of data. think one row, one column. if you want to return a collection you need to call ExecuteReader(). this will return an IDataReader. you can then iterate over the records and return you list.

Answer 2

ExecuteScalar:

Executes the query, and returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.

You need to use SqlDataReader:

SqlCommand command = new SqlCommand(queryString, connection);
IList<int> ints = new List<int>();
using(SqlDataReader reader = command.ExecuteReader()) {
     while (reader.Read())
     {
         ints.add(reader.GetInt32(0)); // provided that first (0-index) column is int which you are looking for
     }
}

Answer 3

ExecuteScalar method returns the first column of the first row in the result set returned by the query. Additional columns or rows are ignored.

If you want to have a list of items, You should use ExecuteReader and loop thru the reader and read the value needed

List<int> items=new List<int>();
using (IDataReader reader = db.ExecuteReader(dbCommand))
{
      while (reader.Read())
      {
         items.Add(reader.GetInt32(reader.GetOrdinal("YourColumnName"));
      }
}

Answer 4

ExecuteScalar( ) - return only first row and first column....

Check msdn : SqlCommand.ExecuteScalar

You need to user something like this to get result i.e ExecuteReader

 using (IDataReader reader = 
        command.ExecuteReader(CommandBehavior.CloseConnection))
 {
      List<int> intlist = ReadList(reader);
 }

method to create list

List<int> ReadList(IDataReader reader)
{
    List<int> list = new List<int>();
    int column = reader.GetOrdinal("MyColumn");

    while (reader.Read())
    {
        //check for the null value and than add 
        if(!SqlReader.IsDBNull(column))
             list.Add(reader.GetInt32(column));
    }

    return list;
}