>I think Rob's right in that if there are a lot of lookups by ColumnName then Dictionary would be faster. OTOH is you wanted, say a list ofcolumns of int Types then IEnumerable would be better....

In my case I output all columns for a table. I normally access column by column name. I already switched to List. Should I switch back to dictionary?

My current classes:

 /// <summary>
   /// Column schema - some properties
   /// </summary>
    public class ColumnSchema
    {
       public String ColumnName { get; set; }
       public Type DataType { get; set; }
       public SqlDbType DbType { get; set; }
       public Int32 ColumnSize { get; set; }
       public Int16 Precision { get; set; }
       public Int16 Scale { get; set; }
       public Boolean IsIdentity { get; set; }
      
       /// <summary>
       /// default constructor
       /// </summary>
       public ColumnSchema()
       {
       }

       public ColumnSchema(String columnName, Type dataType, SqlDbType dbType, Int32 columnSize, Int16 precision, Int16 scale, Boolean isIdentity)
       {
          ColumnName = columnName;
          DataType = dataType;
          DbType = dbType;
          ColumnSize = columnSize;
          Precision = precision;
          Scale = scale;
          IsIdentity = isIdentity;
       }
    }

   /// <summary>
   /// TableSchema class - has a list of columns
   /// </summary>
    public class TableSchema
    {
        internal String TableName;
        internal List<ColumnSchema> Columns = new List<ColumnSchema>();

        public TableSchema(String table, List<ColumnSchema> columnsList)
        {
            TableName = table;
            Columns = columnsList;
        }
       /// <summary>
       /// Returns column's schema
       /// </summary>
       /// <param name="columnName"></param>
       /// <returns></returns>
        internal ColumnSchema GetColumnSchema(String columnName)
        {
           var columnSchema = Columns.Where(x => x.ColumnName == columnName).FirstOrDefault();

            return columnSchema;
        }

        internal Type GetColumnType(String columnName)
        {
           var columnSchema = GetColumnSchema(columnName);
           if (columnSchema==null)
                return null;

            return columnSchema.DataType;
        }

        internal SqlDbType? GetColumnDbType(String columnName)
        {
           var columnSchema = GetColumnSchema(columnName);
           if (columnSchema == null)
              return null;

           return columnSchema.DbType;
        }
    }