using System;
using System.Collections;
using System.Collections.Generic;
using System.ComponentModel;
using System.Dynamic;
using System.Linq;
using System.Runtime.CompilerServices;
using System.Data.Linq;
using System.Data.Linq.Mapping;
using System.Xml;
using System.Runtime.Remoting.Contexts;

namespace ConsoleApp3_Test
{
    internal class Aa
    {

        static void Main(string[] args)
        {            
            DataContext dataContext = new DataContext("server=192.168.1.1,12345;database=test;uid=sa;pwd=111");
            Table<User> Users=dataContext.GetTable<User>();
            
            User query =
                (from user in Users
                 where user.name.Contains("王")
                 select user
                ).
                First();
            Console.WriteLine(query.name); 
        }
    }

    [Table (Name = "c_user")]
    public class User
    {
        [Column(Name = "userid",IsPrimaryKey =true)] public int ID;　　//此处的字段类型错误，数据库中该字段类型为varchar
        [Column (Name = "username")] public string name;
    }
 }

原因：

实体类的字段（ID)的类型与数据库中的类型不一致。实体类的ID类型为int，数据库中的类型为varchar。将实体类中ID字段类型改为string 即可。