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//定义数据模型类public class Base_UserTestDTO : Base_User{
       public string DepartmentName {
    get; set; }}//即BaseBusiness中的Servicevar db = DbFactory.GetRepository();Expression
   
    
     > select = (a, b) => new Base_UserTestDTO{
       DepartmentName = b.Name};select = select.BuildExtendSelectExpre();var q = from a in db.GetIQueryable
     
      ().AsExpandable()        join b in db.GetIQueryable
      
       () on a.DepartmentId equals b.Id into ab        from b in ab.DefaultIfEmpty()        select @select.Invoke(a, b);//筛选var where = LinqHelper.True
       
        ();where = where.And(x => x.UserName == "Admin");//获取筛选数据var list = q.Where(where).ToList();
       
      
     
    
   

public static Expression
   
    
     > BuildExtendSelectExpre
     
      (this Expression
      
       
        > expression){
       return GetExtendSelectExpre
        
         >(expression);}
        
       
      
     
    
   

private static Expression
   
     GetExtendSelectExpre
    
     (Expression
     
       expression){
       NewExpression newBody = Expression.New(typeof(TResult));    MemberInitExpression oldExpression = (MemberInitExpression)expression.Body;    ParameterExpression[] oldParamters = expression.Parameters.ToArray();    List
      
        existsProperties = new List
       
        ();    oldExpression.Bindings.ToList().ForEach(aBinding =>    {
           existsProperties.Add(aBinding.Member.Name);    });    List
        
          newBindings = new List
         
          (); typeof(TBase).GetProperties().Where(x => !existsProperties.Contains(x.Name)).ToList().ForEach(aProperty => { if (typeof(TResult).GetMembers().Any(x => x.Name == aProperty.Name)) { MemberBinding newMemberBinding = null; var valueExpre = Expression.Property(oldParamters[0], aProperty.Name); if (typeof(TBase).IsAssignableFrom(typeof(TResult))) { newMemberBinding = Expression.Bind(aProperty, valueExpre); } else { newMemberBinding = Expression.Bind(typeof(TResult).GetProperty(aProperty.Name), valueExpre); } newBindings.Add(newMemberBinding); } }); newBindings.AddRange(oldExpression.Bindings); var body = Expression.MemberInit(newBody, newBindings.ToArray()); var resExpression = Expression.Lambda
          
           (body, oldParamters); return resExpression;}
          
         
        
       
      
     
    
   

/// 
    /// Linq操作帮助类    /// 
    public static class LinqHelper    {
           /// 
        /// 创建初始条件为True的表达式        /// 
        /// 
           /// 
           public static Expression
   
    
     > True
     
      ()        {
               return x => true;        }        /// 
      
        /// 创建初始条件为False的表达式        /// 
        /// 
              /// 
              public static Expression
      
       
        > False
        
         () { return x => false; } }
        
       
      
     
    
   

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