转换数据表到泛型列表？ [英] Convert DataTable to generic List?

问题描述

    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;
    }

这就是我们能想到的，现在唯一的事情是我们必须做的事情，我们需要收集的垃圾自己？

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

思考？

为什么我们认为有可能是泄漏：？

Why we think there might be a leak?:

我们越来越内存不足的错误。如果页面不需要业务逻辑来使用这种类型的转换，在II6过程不长，但是当我们打一个使用它的页面，它的增长。

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.

目前，我们正在越来越蚂蚁探查给我们更多的细节。

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

推荐答案

这不会是一个实际的泄漏的，但它可以强调不必要的东西...

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

您有多少行工作过？ 需要注意的是反思是一种痛苦，而且每次调用的东西像 GetCustomAttributes 可以返回一个新的数组（所以你想这样做一次，一次也没有按财产per-行）。

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).

就个人而言，我会pre-构建我打算做...类似下面的工作。

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

请注意，如果我这样做很多，我想无论是切换到 HyperDescriptor ，或者.NET 3.5是一个选择，也许是编前pression。由于数据表不是强类型， HyperDescriptor 将（性能）后，下方的合乎逻辑的下一步..

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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