using System;
2 using System.Collections.Generic;
3 using System.Data;
4 using System.Data.Common;
5 using System.Data.SqlClient;
6 using System.Linq;
7 using System.Linq.Expressions;
8 using System.Reflection;
9 using System.Text;
10 using System.Threading.Tasks;
11
12 namespace Demo1
13 {
14 public static class EntityConverter
15 {
16 #region
17 /// <summary>
18 /// DataTable生成实体
19 /// </summary>
20 /// <typeparam name="T"></typeparam>
21 /// <param name="dataTable"></param>
22 /// <returns></returns>
23 public static List<T> ToList<T>(
this DataTable dataTable)
where T :
class,
new()
24 {
25 if (dataTable ==
null || dataTable.Rows.Count <=
0)
throw new ArgumentNullException(
"dataTable",
"当前对象为null无法生成表达式树");
26 Func<DataRow, T> func = dataTable.Rows[
0].ToExpression<T>
();
27 List<T> collection =
new List<T>
(dataTable.Rows.Count);
28 foreach (DataRow dr
in dataTable.Rows)
29 {
30 collection.Add(func(dr));
31 }
32 return collection;
33 }
34
35
36 /// <summary>
37 /// 生成表达式
38 /// </summary>
39 /// <typeparam name="T"></typeparam>
40 /// <param name="dataRow"></param>
41 /// <returns></returns>
42 public static Func<DataRow, T> ToExpression<T>(
this DataRow dataRow)
where T :
class,
new()
43 {
44 if (dataRow ==
null)
throw new ArgumentNullException(
"dataRow",
"当前对象为null 无法转换成实体");
45 ParameterExpression parameter = Expression.Parameter(
typeof(DataRow),
"dr");
46 List<MemberBinding> binds =
new List<MemberBinding>
();
47 for (
int i =
0; i < dataRow.ItemArray.Length; i++
)
48 {
49 String colName =
dataRow.Table.Columns[i].ColumnName;
50 PropertyInfo pInfo =
typeof(T).GetProperty(colName);
51 if (pInfo ==
null || !pInfo.CanWrite)
continue;
52 MethodInfo mInfo =
typeof(DataRowExtensions).GetMethod(
"Field",
new Type[] {
typeof(DataRow),
typeof(String) }).MakeGenericMethod(pInfo.PropertyType);
53 MethodCallExpression call = Expression.Call(mInfo, parameter, Expression.Constant(colName,
typeof(String)));
54 MemberAssignment bind =
Expression.Bind(pInfo, call);
55 binds.Add(bind);
56 }
57 MemberInitExpression init = Expression.MemberInit(Expression.New(
typeof(T)), binds.ToArray());
58 return Expression.Lambda<Func<DataRow, T>>
(init, parameter).Compile();
59 }
60 #endregion
61 /// <summary>
62 /// 生成lambda表达式
63 /// </summary>
64 /// <typeparam name="T"></typeparam>
65 /// <param name="reader"></param>
66 /// <returns></returns>
67 public static Func<SqlDataReader, T> ToExpression<T>(
this SqlDataReader reader)
where T :
class,
new()
68 {
69 if (reader ==
null || reader.IsClosed || !reader.HasRows)
throw new ArgumentException(
"reader",
"当前对象无效");
70 ParameterExpression parameter = Expression.Parameter(
typeof(SqlDataReader),
"reader");
71 List<MemberBinding> binds =
new List<MemberBinding>
();
72 for (
int i =
0; i < reader.FieldCount; i++
)
73 {
74 String colName =
reader.GetName(i);
75 PropertyInfo pInfo =
typeof(T).GetProperty(colName);
76 if (pInfo ==
null || !pInfo.CanWrite)
continue;
77 MethodInfo mInfo = reader.GetType().GetMethod(
"GetFieldValue").MakeGenericMethod(pInfo.PropertyType);
78 MethodCallExpression call =
Expression.Call(parameter, mInfo, Expression.Constant(i));
79 MemberAssignment bind =
Expression.Bind(pInfo, call);
80 binds.Add(bind);
81 }
82 MemberInitExpression init = Expression.MemberInit(Expression.New(
typeof(T)), binds.ToArray());
83 return Expression.Lambda<Func<SqlDataReader, T>>
(init, parameter).Compile();
84 }
85
86 }
87 }
在上一篇的基础上增加了 SqlDataReader 的扩展方法
以下代码是调用
1 using System;
2 using System.Collections.Generic;
3 using System.Data;
4 using System.Data.Common;
5 using System.Data.SqlClient;
6 using System.Diagnostics;
7 using System.Linq;
8 using System.Reflection;
9 using System.Text;
10 using System.Threading.Tasks;
11
12 namespace Demo1
13 {
14 class Program
15 {
16 static void Main(string[] args)
17 {
18 String conString = "Data Source=.; Initial Catalog=master; Integrated Security=true;";
19 Func<SqlDataReader, Usr> func = null;
20 List<Usr> usrs = new List<Usr>();
21 using (SqlDataReader reader = GetReader(conString, "select object_id ‘ID‘,name ‘Name‘ from sys.objects", CommandType.Text, null))
22 {
23 while (reader.Read())
24 {
25 if (func == null)
26 {
27 func = reader.ToExpression<Usr>();
28 }
29 Usr usr = func(reader);
30 usrs.Add(usr);
31 }
32 }
33 usrs.Clear();
34 Console.ReadKey();
35 }
36
37 public static SqlDataReader GetReader(String conString, String sql, CommandType type, params SqlParameter[] pms)
38 {
39 SqlConnection conn = new SqlConnection(conString);
40 SqlCommand cmd = new SqlCommand(sql, conn);
41 cmd.CommandType = type;
42 if (pms != null && pms.Count() > 0)
43 {
44 cmd.Parameters.AddRange(pms);
45 }
46 conn.Open();
47 return cmd.ExecuteReader(CommandBehavior.CloseConnection);
48 }
49 }
50 class Usr
51 {
52 public Int32 ID { get; set; }
53 public String Name { get; set; }
54 }
55
56
57 }
目前只能处理sqlserver返回的对象，处理其它数据库本来是想增加 DbDataReader 的扩展方法，但发现动态生成lambda表达式的地方出错，所以先将现在的
方案记录下来。
文中如果有不清楚或者有问题的地方请园友指出。谢谢。
原创作品，转载请注明出处：http://www.cnblogs.com/lclblog/p/6711292.html
SqlDataReader生成动态Lambda表达式
标签：datarow expr icm close cli cut uri console clear
