//判断右表是否为空并为映射表进行赋值标志

var query=from q in product
          join m in favProduct
          on q.Name equals m.Name into t
          from x in t.DefalultEmpty()
          select new
          {
             Name=q.Name,
             fav=x!=null/fav=x=null?false:true
　　　　　　}