我有几个返回不同泛型列表的方法。
在 .net 中是否存在将任何列表转换为数据表的类静态方法或其他方法?我唯一能想象的就是使用反射来实现这一点。
如果我有以下内容:
List<Whatever> whatever = new List<Whatever>();
(当然,以下代码不能正常工作,但我希望有这个可能性:
DataTable dt = (DataTable) whatever;
我有几个返回不同泛型列表的方法。
在 .net 中是否存在将任何列表转换为数据表的类静态方法或其他方法?我唯一能想象的就是使用反射来实现这一点。
如果我有以下内容:
List<Whatever> whatever = new List<Whatever>();
(当然,以下代码不能正常工作,但我希望有这个可能性:
DataTable dt = (DataTable) whatever;
以下是使用NuGet中的FastMember进行的2013年更新:
IEnumerable<SomeType> data = ...
DataTable table = new DataTable();
using(var reader = ObjectReader.Create(data)) {
table.Load(reader);
}
IEnumerable<SomeType> data = ...
DataTable table = new DataTable();
using(var reader = ObjectReader.Create(data, "Id", "Name", "Description")) {
table.Load(reader);
}
编辑的免责声明:FastMember 是 Marc Gravell 的项目。它很好用,而且非常流畅!
是的,这基本上是这个的完全相反;反射就足够了 - 或者如果您需要更快的话,在2.0中使用HyperDescriptor
,或者在3.5中使用Expression
。实际上,HyperDescriptor
应该足够了。
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,您就可以通过启用对象类型T
的HyperDescriptor
,使其比反射快很多倍。
编辑关于性能查询的内容;这里是一个带有结果的测试装置:
Vanilla 27179
Hyper 6997
我怀疑瓶颈已经从成员访问转移到了DataTable
性能上...我不认为你会在这方面有太大的改进...
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
}
}
我不得不修改Marc Gravell的示例代码,以处理可空类型和空值。我在下面包含了一个可工作的版本。谢谢Marc。
public static DataTable ToDataTable<T>(this IList<T> data)
{
PropertyDescriptorCollection properties =
TypeDescriptor.GetProperties(typeof(T));
DataTable table = new DataTable();
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)
row[prop.Name] = prop.GetValue(item) ?? DBNull.Value;
table.Rows.Add(row);
}
return table;
}
public static DataTable ToDataTable<TKey, T>(this IEnumerable<IGrouping<TKey, T>> data)
然后,在foreach循环之前添加一个额外的列:table.Columns.Add("Key", Nullable.GetUnderlyingType(typeof(TKey)) ?? typeof(TKey));
接下来,在遍历数据组时,需要在数据循环周围添加一个循环:foreach (IGrouping<TKey, T> group in data)
{
foreach (T item in group.Items)
{请参考此GIST获取完整信息:
https://gist.github.com/rickdailey/8679306 - Rick DaileyToDataTable
方法中有一个难以察觉的 bug。如果 T
实现了一个接口,则 typeof(T)
可能会返回接口类型而不是对象的实际类,导致 DataTable
为空。将其替换为 data.First().GetType()
应该可以解决问题。 - Janilson另一种方法如下:
List<WhateEver> lst = getdata();
string json = Newtonsoft.Json.JsonConvert.SerializeObject(lst);
DataTable pDt = JsonConvert.DeserializeObject<DataTable>(json);
这是解决方案的简单混合体。
它适用于可空类型。
public static DataTable ToDataTable<T>(this IList<T> list)
{
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, Nullable.GetUnderlyingType(prop.PropertyType) ?? prop.PropertyType);
}
object[] values = new object[props.Count];
foreach (T item in list)
{
for (int i = 0; i < values.Length; i++)
values[i] = props[i].GetValue(item) ?? DBNull.Value;
table.Rows.Add(values);
}
return table;
}
对Marc的回答做了一点小修改,使它能够适用于像List<string>
这样的值类型到数据表:
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;
}
这个MSDN链接值得一看:如何:实现CopyToDataTable<T>方法,其中的泛型类型T不是DataRow
它添加了一个扩展方法使你可以这样做:
// Create a sequence.
Item[] items = new Item[]
{ new Book{Id = 1, Price = 13.50, Genre = "Comedy", Author = "Gustavo Achong"},
new Book{Id = 2, Price = 8.50, Genre = "Drama", Author = "Jessie Zeng"},
new Movie{Id = 1, Price = 22.99, Genre = "Comedy", Director = "Marissa Barnes"},
new Movie{Id = 1, Price = 13.40, Genre = "Action", Director = "Emmanuel Fernandez"}};
// Query for items with price greater than 9.99.
var query = from i in items
where i.Price > 9.99
orderby i.Price
select i;
// Load the query results into new DataTable.
DataTable table = query.CopyToDataTable();
List<YourModel> data = new List<YourModel>();
DataTable dataTable = Newtonsoft.Json.JsonConvert.DeserializeObject<DataTable>(Newtonsoft.Json.JsonConvert.SerializeObject(data));
public DataTable ConvertToDataTable<T>(IList<T> data)
{
PropertyDescriptorCollection properties =
TypeDescriptor.GetProperties(typeof(T));
DataTable table = new DataTable();
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)
{
row[prop.Name] = prop.GetValue(item) ?? DBNull.Value;
}
table.Rows.Add(row);
}
return table;
}
试一试
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;
}
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.