A simply Linq entity base class

/********************************************************************************************************************************
 * Jin Tu 
 * 2010-11-16
 * 
 * Entity inherited from this base class will implement functions:
 * 1. use new keyword to create an instance, add it to database
 * 2. get an entity from database, then delete it
 * 3. get an entity from database, then update it
 * 
 * Also, base class provides two static functions:
 * 1. get all entities
 * 2. get one entity with primary key field parameters 
 * 3. compare with lamdba expression to get entity list
 * 
 * 
 * ***************************************************************************************************************************/

#define DEBUGGING

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;
using System.Data.Linq;
using System.Data.Linq.Mapping;
using System.Reflection;
using System.Linq.Expressions;


namespace Tj.Linq
{
    public class BaseEntity<TEntity, TContext>
        where TEntity : class, new()
        where TContext : DataContext, new()
    {
        static TContext _context = null;
        Table<TEntity> _table = null;

        static BaseEntity()
        {
            CreateContext();
        }

        static void CreateContext()
        {
            if(_context==null)
                _context = Activator.CreateInstance<TContext>() as TContext;
        }

        void InitializeEntity()
        {

            _table = _context.GetTable<TEntity>();
        }

        public bool Add()
        {
            try
            {
                InitializeEntity();
                _table.InsertOnSubmit(this as TEntity);
                _context.SubmitChanges(ConflictMode.ContinueOnConflict);
            }
            catch (ChangeConflictException)
            {
                _context.ChangeConflicts.ResolveAll(RefreshMode.KeepCurrentValues);
                _context.SubmitChanges();
            }
            catch (System.Exception ex)
            {
#if DEBUGGING
                throw ex;
#else
                 return false;
#endif
            }

            return true;

        }

   

      public  bool Update()
        {
            try
            {
                InitializeEntity();
                
                _context.SubmitChanges(ConflictMode.ContinueOnConflict);
            }
            catch (ChangeConflictException)
            {
                _context.ChangeConflicts.ResolveAll(RefreshMode.KeepCurrentValues);
                _context.SubmitChanges();
            }
            catch (System.Exception ex)
            {
#if DEBUGGING
                throw ex;
#else
                 return false;
#endif
            }

            return true;
        }

        public bool Delete()
        {
            try
            {
                InitializeEntity();
                _table.DeleteOnSubmit(this as TEntity);
                _context.SubmitChanges(ConflictMode.ContinueOnConflict);
            }
            catch (ChangeConflictException)
            {
                _context.ChangeConflicts.ResolveAll(RefreshMode.KeepCurrentValues);
                _context.SubmitChanges();
            }
            catch (System.Exception ex)
            {
#if DEBUGGING
                throw ex;
#else
                 return false;
#endif
            }

            return true;

        }


        public static IList<TEntity> GetAll()
        {

            return _context.GetTable<TEntity>().Where(c=>c!=null).ToList();

        }

       /// <summary>
        /// get one entity with primary key field parameters 
       /// </summary>
       /// <param name="values">the values of each primary key field</param>
       /// <returns>entity</returns>
        public static TEntity GetByPk(object[] values)
        {

            Table<TEntity> table = _context.GetTable<TEntity>();
            MetaTable metaTable = _context.Mapping.GetTable(typeof(TEntity));
            List<MetaDataMember> pks = metaTable.RowType.DataMembers.Where(c => c.IsPrimaryKey).ToList();
            if (pks == null)
                throw new Exception("have no pk !");


            string cond = null;
           
            for (int i = 0; i < pks.Count(); i++)
            {              
                    cond += pks[i].MappedName + "==@" + i.ToString() + " and ";
            }

            cond = cond.Substring(0, cond.Length - 5);

           // Expression parse;
            ParameterExpression param = Expression.Parameter(typeof(TEntity), "c");// "c" indicates TEntity object
 
            string[] conds=cond.Split(new string[1]{"and"},StringSplitOptions.RemoveEmptyEntries);
            Expression left=null;
            Expression right=null;
            Expression body = null;
            List<BinaryExpression> binExps = new List<BinaryExpression>();
            for (int i = 0; i < conds.Length;i++ )
            {
                string fieldname="_"+conds[i].Split(new string[1]{"=="},StringSplitOptions.RemoveEmptyEntries)[0].Trim();
                left = Expression.Field(param, typeof(TEntity).GetField(fieldname, BindingFlags.Instance | BindingFlags.NonPublic));
                right = Expression.Constant(values[i]);
                binExps.Add(Expression.Equal(left, right));//c.pk1=1 
            }

            body = binExps[0];
            for(int i=1; i<binExps.Count();i=i+2)
            {
                body = Expression.And(body, binExps[i]);//c=>c.pk1=1 and c.pk2="2" ....
            }          

            LambdaExpression lamda = Expression.Lambda(body, param);           

            //search
            TEntity[] entities = table.Where((Func<TEntity, bool>)lamda.Compile()).ToArray();


            if (entities.Length == 1)
                return entities[0];
            return null;
        }

        public static IList<TEntity> GetByConditon(Expression<Func<TEntity, bool>> predicate)
        {
            Table<TEntity> table = _context.GetTable<TEntity>();
            return table.Where(predicate).ToList();

        }
    }
}

To use it, the next is examples:

1. dbml file 

 2.Use base class to Role entity class

using System;
using System.Collections.Generic;
using System.Linq;
using System.Text;

namespace ConsoleApplication2
{
    public partial class Role : Tj.Linq.BaseEntity<Role, DataClasses1DataContext>
    {
    }
}

 3. entity use examples:

 

using System;
using System.Collections.Generic;
using System.Text;


namespace ConsoleApplication2
{
    class Program
    {
        static void Main(string[] args)
        {
            ////add
            //Role role = new Role();
            //role.Role_Name = "test";           
            //role.Add();

            //get all
            IList<Role> lstrole= Role.GetAll();

            //get by primary key
            Role role = Role.GetByPk(new object[2] { 3, "test" });


           // role.Role_Name = "test555";
       
           // role.Update(); //update
           // role.Delete();//delete

            //get by lamdba expression
            IList<Role> lst = Role.GetByConditon(c => c.Role_ID == 3 && c.Role_Name =="test");
        }
    }
}