大数据量下DataTable To List效率对比

使用反射和动态生成代码两种方式（reflect和emit）

反射将datatable转为list方法

 1 public static list<t> tolistbyreflect<t>(this datatable dt) where t : new()
 2         {
 3             list<t> ts = new list<t>();
 4             string tempname = string.empty;
 5             foreach (datarow dr in dt.rows)
 6             {
 7                 t t = new t();
 8                 propertyinfo[] propertys = t.gettype().getproperties();
 9                 foreach (propertyinfo pi in propertys)
10                 {
11                     tempname = pi.name;
12                     if (dt.columns.contains(tempname))
13                     {
14                         object value = dr[tempname];
15                         if (value != dbnull.value)
16                         {
17                             pi.setvalue(t, value, null);
18                         }
19                     }
20                 }
21                 ts.add(t);
22             }
23             return ts;
24         }

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动态生成代码将datatable转为list方法

 1 public static list<t> tolistbyemit<t>(this datatable dt) where t : class, new()
 2         {
 3             list<t> list = new list<t>();
 4             if (dt == null || dt.rows.count == 0)
 5                 return list;
 6             datatableentitybuilder<t> eblist = datatableentitybuilder<t>.createbuilder(dt.rows[0]);
 7             foreach (datarow info in dt.rows)
 8                 list.add(eblist.build(info));
 9             dt.dispose();
10             dt = null;
11             return list;
12         }
13         public class datatableentitybuilder<entity>
14         {
15             private static readonly methodinfo getvaluemethod = typeof(datarow).getmethod("get_item", new type[] { typeof(int) });
16             private static readonly methodinfo isdbnullmethod = typeof(datarow).getmethod("isnull", new type[] { typeof(int) });
17             private delegate entity load(datarow datarecord);
18             private load handler;
19             private datatableentitybuilder() { }
20             public entity build(datarow datarecord)
21             {
22                 return handler(datarecord);
23             }
24             public static datatableentitybuilder<entity> createbuilder(datarow datarecord)
25             {
26                 datatableentitybuilder<entity> dynamicbuilder = new datatableentitybuilder<entity>();
27                 dynamicmethod method = new dynamicmethod("dynamiccreateentity", typeof(entity), new type[] { typeof(datarow) }, typeof(entity), true);
28                 ilgenerator generator = method.getilgenerator();
29                 localbuilder result = generator.declarelocal(typeof(entity));
30                 generator.emit(opcodes.newobj, typeof(entity).getconstructor(type.emptytypes));
31                 generator.emit(opcodes.stloc, result);
32                 for (int i = 0; i < datarecord.itemarray.length; i++)
33                 {
34                     propertyinfo propertyinfo = typeof(entity).getproperty(datarecord.table.columns[i].columnname);
35                     label endiflabel = generator.definelabel();
36                     if (propertyinfo != null && propertyinfo.getsetmethod() != null)
37                     {
38                         generator.emit(opcodes.ldarg_0);
39                         generator.emit(opcodes.ldc_i4, i);
40                         generator.emit(opcodes.callvirt, isdbnullmethod);
41                         generator.emit(opcodes.brtrue, endiflabel);
42                         generator.emit(opcodes.ldloc, result);
43                         generator.emit(opcodes.ldarg_0);
44                         generator.emit(opcodes.ldc_i4, i);
45                         generator.emit(opcodes.callvirt, getvaluemethod);
46                         generator.emit(opcodes.unbox_any, propertyinfo.propertytype);
47                         generator.emit(opcodes.callvirt, propertyinfo.getsetmethod());
48                         generator.marklabel(endiflabel);
49                     }
50                 }
51                 generator.emit(opcodes.ldloc, result);
52                 generator.emit(opcodes.ret);
53                 dynamicbuilder.handler = (load)method.createdelegate(typeof(load));
54                 return dynamicbuilder;
55             }
56         }

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然后写个控制台程序，对比一下两个方法的效率（测试类大概有40个属性）

电脑比较渣，使用emit方法转换100w条数据大概需要7秒，而反射则需要37秒。还测试了当数据量比较小时，reflect反而比较快。