Convert DataTable to generic List?

12,707

That won't be an actual leak, but it could be stressing things unnecessarily...

How many rows are you working over? Note that reflection is a pain, and that every call to things like GetCustomAttributes can return a new array (so you want to do that once, not once per-property-per-row).

Personally, I'd pre-construct the work I intend to do... something like below.

Note that if I was doing this lots, I'd either switch to HyperDescriptor, or if .NET 3.5 was an option, maybe a compiled Expression. Since DataTable isn't strongly typed, HyperDescriptor would be a logical next step (for performance) after the below...

sealed class Tuple<T1, T2>
{
    public Tuple() {}
    public Tuple(T1 value1, T2 value2) {Value1 = value1; Value2 = value2;}
    public T1 Value1 {get;set;}
    public T2 Value2 {get;set;}
}
public static List<T> Convert<T>(DataTable table)
    where T : class, new()
{
    List<Tuple<DataColumn, PropertyInfo>> map =
        new List<Tuple<DataColumn,PropertyInfo>>();

    foreach(PropertyInfo pi in typeof(T).GetProperties())
    {
        ColumnAttribute col = (ColumnAttribute)
            Attribute.GetCustomAttribute(pi, typeof(ColumnAttribute));
        if(col == null) continue;
        if(table.Columns.Contains(col.FieldName))
        {
            map.Add(new Tuple<DataColumn,PropertyInfo>(
                table.Columns[col.FieldName], pi));
        }
    }

    List<T> list = new List<T>(table.Rows.Count);
    foreach(DataRow row in table.Rows)
    {
        if(row == null)
        {
            list.Add(null);
            continue;
        }
        T item = new T();
        foreach(Tuple<DataColumn,PropertyInfo> pair in map) {
            object value = row[pair.Value1];
            if(value is DBNull) value = null;
            pair.Value2.SetValue(item, value, null);
        }
        list.Add(item);
    }
    return list;        
}
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12,707
user3237201
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user3237201

Updated on June 18, 2022

Comments

  • user3237201
    user3237201 almost 2 years
        public static IList<T> ConvertTo<T>(DataTable table)
        {
            if (table == null)
            {
                return null;
            }
    
            List<DataRow> rows = new List<DataRow>();
    
            foreach (DataRow row in table.Rows)
            {
                rows.Add(row);
            }
    
            return ConvertTo<T>(rows);
        }
    
        public static T ConvertItem<T>(DataTable table)
        {
            T obj = default(T);
            if (table != null && table.Rows.Count > 0)
            {
                obj = CreateItem<T>(table.Rows[0]);
            }
            return obj;
        }
    
    
        public static T CreateItem<T>(DataRow row)
        {
            T obj = default(T);
            if (row != null)
            {
                obj = Activator.CreateInstance<T>();
                Type entityType = typeof(T);
                PropertyInfo[] properties = entityType.GetProperties();
    
                for (int i = 0; i < properties.Length; i++)
                {
                    object[] customAttributes = properties[i].GetCustomAttributes(typeof(ColumnAttributes), false);
                    ColumnAttributes dataField = null;
                    if (null != customAttributes && customAttributes.Length > 0 && null != (dataField = customAttributes[0] as ColumnAttributes))
                    {
                        if (row.Table.Columns.Contains(dataField.FieldName) && !row[dataField.FieldName].GetType().FullName.Equals("System.DBNull"))
                        {
                            properties[i].SetValue(obj, row[dataField.FieldName], null);
                        }
                    }
                }
            }
            return obj;
        }
    

    Thats the only thing we can think of right now is that we must be doing something where we need to Garbage collect Ourselves?

    Thoughts?

    Why we think there might be a leak?:

    We are getting Out of Memory Errors. If a Page does not require business logic to use this type of conversion, the II6 process does not grow, but when we hit a page that uses it, it grows.

    We are currently getting ANTS Profiler to give us more details.

  • Rune Grimstad
    Rune Grimstad about 15 years
    I agree with Marc. Your code is both slow and quite complicated! Also you should check the types of the properties so you don't try to set the value of an int to a string value and so on.