我有几个方法返回不同的泛型列表。
在。net中存在任何类静态方法或将任何列表转换为数据表?我唯一能想到的是使用反射来做到这一点。
如果我有这个:
List<Whatever> whatever = new List<Whatever>();
(这下代码当然不工作,但我想有这样的可能性:
DataTable dt = (DataTable) whatever;
我有几个方法返回不同的泛型列表。
在。net中存在任何类静态方法或将任何列表转换为数据表?我唯一能想到的是使用反射来做到这一点。
如果我有这个:
List<Whatever> whatever = new List<Whatever>();
(这下代码当然不工作,但我想有这样的可能性:
DataTable dt = (DataTable) whatever;
当前回答
这是一个简单的控制台应用程序,用于将列表转换为数据表。
using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data;
using System.ComponentModel;
namespace ConvertListToDataTable
{
public static class Program
{
public static void Main(string[] args)
{
List<MyObject> list = new List<MyObject>();
for (int i = 0; i < 5; i++)
{
list.Add(new MyObject { Sno = i, Name = i.ToString() + "-KarthiK", Dat = DateTime.Now.AddSeconds(i) });
}
DataTable dt = ConvertListToDataTable(list);
foreach (DataRow row in dt.Rows)
{
Console.WriteLine();
for (int x = 0; x < dt.Columns.Count; x++)
{
Console.Write(row[x].ToString() + " ");
}
}
Console.ReadLine();
}
public class MyObject
{
public int Sno { get; set; }
public string Name { get; set; }
public DateTime Dat { get; set; }
}
public static DataTable ConvertListToDataTable<T>(this List<T> iList)
{
DataTable dataTable = new DataTable();
PropertyDescriptorCollection props = TypeDescriptor.GetProperties(typeof(T));
for (int i = 0; i < props.Count; i++)
{
PropertyDescriptor propertyDescriptor = props[i];
Type type = propertyDescriptor.PropertyType;
if (type.IsGenericType && type.GetGenericTypeDefinition() == typeof(Nullable<>))
type = Nullable.GetUnderlyingType(type);
dataTable.Columns.Add(propertyDescriptor.Name, type);
}
object[] values = new object[props.Count];
foreach (T iListItem in iList)
{
for (int i = 0; i < values.Length; i++)
{
values[i] = props[i].GetValue(iListItem);
}
dataTable.Rows.Add(values);
}
return dataTable;
}
}
}
其他回答
如果你的类中有属性,这行代码是OK的!!
PropertyDescriptorCollection props =
TypeDescriptor.GetProperties(typeof(T));
但如果你有所有的公共字段,那么使用这个:
public static DataTable ToDataTable<T>( IList<T> data)
{
FieldInfo[] myFieldInfo;
Type myType = typeof(T);
// Get the type and fields of FieldInfoClass.
myFieldInfo = myType.GetFields(BindingFlags.NonPublic | BindingFlags.Instance
| BindingFlags.Public);
DataTable dt = new DataTable();
for (int i = 0; i < myFieldInfo.Length; i++)
{
FieldInfo property = myFieldInfo[i];
dt.Columns.Add(property.Name, property.FieldType);
}
object[] values = new object[myFieldInfo.Length];
foreach (T item in data)
{
for (int i = 0; i < values.Length; i++)
{
values[i] = myFieldInfo[i].GetValue(item);
}
dt.Rows.Add(values);
}
return dt;
}
原来的答案是从上面,我只是编辑使用字段而不是属性
然后这样使用它
DataTable dt = new DataTable();
dt = ToDataTable(myBriefs);
gridData.DataSource = dt;
gridData.DataBind();
下面是NuGet使用FastMember的2013年更新:
IEnumerable<SomeType> data = ...
DataTable table = new DataTable();
using(var reader = ObjectReader.Create(data)) {
table.Load(reader);
}
它使用FastMember的元编程API来获得最大的性能。如果你想将它限制到特定的成员(或强制执行顺序),那么你也可以这样做:
IEnumerable<SomeType> data = ...
DataTable table = new DataTable();
using(var reader = ObjectReader.Create(data, "Id", "Name", "Description")) {
table.Load(reader);
}
FastMember是Marc Gravell的一个项目。它是金色的,完全是苍蝇!
是的,这个和这个完全相反;反射就足够了——或者如果你需要更快,2.0中的HyperDescriptor,或者3.5中的Expression。实际上,HyperDescriptor应该绰绰有余。
例如:
// remove "this" if not on C# 3.0 / .NET 3.5
public static DataTable ToDataTable<T>(this IList<T> data)
{
PropertyDescriptorCollection props =
TypeDescriptor.GetProperties(typeof(T));
DataTable table = new DataTable();
for(int i = 0 ; i < props.Count ; i++)
{
PropertyDescriptor prop = props[i];
table.Columns.Add(prop.Name, prop.PropertyType);
}
object[] values = new object[props.Count];
foreach (T item in data)
{
for (int i = 0; i < values.Length; i++)
{
values[i] = props[i].GetValue(item);
}
table.Rows.Add(values);
}
return table;
}
现在,只需一行代码,你就可以让它比反射快很多很多倍(通过为对象类型T启用HyperDescriptor)。
编辑重新性能查询;下面是测试结果:
Vanilla 27179
Hyper 6997
我怀疑瓶颈已经从成员访问转移到数据表性能…我怀疑你在这方面还能提高多少……
代码:
using System;
using System.Collections.Generic;
using System.ComponentModel;
using System.Data;
using System.Diagnostics;
public class MyData
{
public int A { get; set; }
public string B { get; set; }
public DateTime C { get; set; }
public decimal D { get; set; }
public string E { get; set; }
public int F { get; set; }
}
static class Program
{
static void RunTest(List<MyData> data, string caption)
{
GC.Collect(GC.MaxGeneration, GCCollectionMode.Forced);
GC.WaitForPendingFinalizers();
GC.WaitForFullGCComplete();
Stopwatch watch = Stopwatch.StartNew();
for (int i = 0; i < 500; i++)
{
data.ToDataTable();
}
watch.Stop();
Console.WriteLine(caption + "\t" + watch.ElapsedMilliseconds);
}
static void Main()
{
List<MyData> foos = new List<MyData>();
for (int i = 0 ; i < 5000 ; i++ ){
foos.Add(new MyData
{ // just gibberish...
A = i,
B = i.ToString(),
C = DateTime.Now.AddSeconds(i),
D = i,
E = "hello",
F = i * 2
});
}
RunTest(foos, "Vanilla");
Hyper.ComponentModel.HyperTypeDescriptionProvider.Add(
typeof(MyData));
RunTest(foos, "Hyper");
Console.ReadLine(); // return to exit
}
}
试试这个
public static DataTable ListToDataTable<T>(IList<T> lst)
{
currentDT = CreateTable<T>();
Type entType = typeof(T);
PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(entType);
foreach (T item in lst)
{
DataRow row = currentDT.NewRow();
foreach (PropertyDescriptor prop in properties)
{
if (prop.PropertyType == typeof(Nullable<decimal>) || prop.PropertyType == typeof(Nullable<int>) || prop.PropertyType == typeof(Nullable<Int64>))
{
if (prop.GetValue(item) == null)
row[prop.Name] = 0;
else
row[prop.Name] = prop.GetValue(item);
}
else
row[prop.Name] = prop.GetValue(item);
}
currentDT.Rows.Add(row);
}
return currentDT;
}
public static DataTable CreateTable<T>()
{
Type entType = typeof(T);
DataTable tbl = new DataTable(DTName);
PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(entType);
foreach (PropertyDescriptor prop in properties)
{
if (prop.PropertyType == typeof(Nullable<decimal>))
tbl.Columns.Add(prop.Name, typeof(decimal));
else if (prop.PropertyType == typeof(Nullable<int>))
tbl.Columns.Add(prop.Name, typeof(int));
else if (prop.PropertyType == typeof(Nullable<Int64>))
tbl.Columns.Add(prop.Name, typeof(Int64));
else
tbl.Columns.Add(prop.Name, prop.PropertyType);
}
return tbl;
}
对Marc的答案做了一个小更改,使其与List<string> to data table等值类型一起工作:
public static DataTable ListToDataTable<T>(IList<T> data)
{
DataTable table = new DataTable();
//special handling for value types and string
if (typeof(T).IsValueType || typeof(T).Equals(typeof(string)))
{
DataColumn dc = new DataColumn("Value", typeof(T));
table.Columns.Add(dc);
foreach (T item in data)
{
DataRow dr = table.NewRow();
dr[0] = item;
table.Rows.Add(dr);
}
}
else
{
PropertyDescriptorCollection properties = TypeDescriptor.GetProperties(typeof(T));
foreach (PropertyDescriptor prop in properties)
{
table.Columns.Add(prop.Name, Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType);
}
foreach (T item in data)
{
DataRow row = table.NewRow();
foreach (PropertyDescriptor prop in properties)
{
try
{
row[prop.Name] = prop.GetValue(item) ?? DBNull.Value;
}
catch (Exception ex)
{
row[prop.Name] = DBNull.Value;
}
}
table.Rows.Add(row);
}
}
return table;
}
It's also possible through XmlSerialization.
The idea is - serialize to `XML` and then `readXml` method of `DataSet`.
I use this code (from an answer in SO, forgot where)
public static string SerializeXml<T>(T value) where T : class
{
if (value == null)
{
return null;
}
XmlSerializer serializer = new XmlSerializer(typeof(T));
XmlWriterSettings settings = new XmlWriterSettings();
settings.Encoding = new UnicodeEncoding(false, false);
settings.Indent = false;
settings.OmitXmlDeclaration = false;
// no BOM in a .NET string
using (StringWriter textWriter = new StringWriter())
{
using (XmlWriter xmlWriter = XmlWriter.Create(textWriter, settings))
{
serializer.Serialize(xmlWriter, value);
}
return textWriter.ToString();
}
}
so then it's as simple as:
string xmlString = Utility.SerializeXml(trans.InnerList);
DataSet ds = new DataSet("New_DataSet");
using (XmlReader reader = XmlReader.Create(new StringReader(xmlString)))
{
ds.Locale = System.Threading.Thread.CurrentThread.CurrentCulture;
ds.ReadXml(reader);
}
Not sure how it stands against all the other answers to this post, but it's also a possibility.