DataTable To List<T> DataTable Linq学习笔记

LINQ 查询适用于实现的数据源 IEnumerable<T>接口或System.Query.IQueryable接口。 

DataTable类默认是没有实现以上接口的。

所以要在DataTable中使用LINQ查询，需要调用一下AsEnumerable方法，返回一个EnumerableRowCollection<DataRow>集合。

实例如下所示：

using System;
using System.Collections.Generic;
using System.Data;
using System.Linq;
using System.Windows.Forms;

namespace DataTableToList
{
    public partial class Form1 : Form
    {
        public Form1()
        {
            InitializeComponent();
        }

        private DataTable GetTable()
        {
            int[] id = { 4, 5, 1, 3, 2, 7, 6 };
            string[] name = { "Tom", "Jack", "Jime", "Lilei", "Jimo", "Koko", "Luoyi" };
            DataTable table = new DataTable("Student");
            table.Columns.Add("ID", typeof(int));
            table.Columns.Add("Name", typeof(string));

            for (int i = 0; i < id.Length; i++)
            {
                table.Rows.Add(new object[] { id[i], name[i] });
            }

            return table;
        }
        //order by
        private void button1_Click(object sender, EventArgs e)
        {
            DataTable dt = GetTable();
            var students = dt.AsEnumerable();

            //排序
            var result = students.OrderBy(x => x.Field<int>("ID"));
            //输出
            this.listBox1.Items.Clear();
            foreach (DataRow row in result)
            {
                this.listBox1.Items.Add("order by=="+row["ID"].ToString() + "==" + row["Name"].ToString());
            }
        }
        //where
        private void btnWhere_Click(object sender, EventArgs e)
        {
            DataTable dt = GetTable();
            var students = dt.AsEnumerable();
            //排序
            var result = students.Where(x => x.Field<int>("ID") > 3);
            //输出
            this.listBox1.Items.Clear();
            foreach (DataRow row in result)
            {
                this.listBox1.Items.Add("where=="+row["ID"].ToString() + "==" + row["Name"].ToString());
            }
        }

        private void btnToList_Click(object sender, EventArgs e)
        {
            DataTable dt = GetTable();
            var students = dt.AsEnumerable();
            List<Student> list = students.Select
                (
                   x => new Student
                    {
                        ID = x.Field<int>("ID"),
                        Name = x.Field<string>("Name")
                    }
                ).ToList();

            this.listBox1.Items.Clear();
            foreach (Student item in list)
            {
                this.listBox1.Items.Add("tolist=="+item.ID + "==" + item.Name);
            }
        }

    }

    public class Student
    {
        public int ID { get; set; }
        public string Name { get; set; }
    }
}

运行效果如下：

方式二：

/// <summary>
        /// DataTable转成List
        /// </summary>
        /// <typeparam name="T"></typeparam>
        /// <param name="dt"></param>
        /// <returns></returns>
        public static List<T> DataTableToList<T>(this DataTable dt)
        {
            var list = new List<T>();
            var plist = new List<PropertyInfo>(typeof(T).GetProperties());
            foreach (DataRow item in dt.Rows)
            {
                T s = Activator.CreateInstance<T>();
                for (int i = 0; i < dt.Columns.Count; i++)
                {
                    PropertyInfo info = plist.Find(p => p.Name == dt.Columns[i].ColumnName);
                    if (info != null)
                    {
                        try
                        {
                            if (!Convert.IsDBNull(item[i]))
                            {
                                object v = null;
                                if (info.PropertyType.ToString().Contains("System.Nullable"))
                                    v = Convert.ChangeType(item[i], Nullable.GetUnderlyingType(info.PropertyType));
                                else v = Convert.ChangeType(item[i], info.PropertyType);
                                info.SetValue(s, v, null);
                            }
                        }
                        catch (Exception ex)
                        {
                            throw new Exception("字段[" + info.Name + "]转换出错," + ex.Message);
                        }
                    }
                }
                list.Add(s);
            }
            return list;
        }