Question

I have an ASPX page that collects 5 optional search criteria from a user and returns the result in a grid. Once the criteria are collected and the view button clicked, the code behind generates the filter like we have below

// aSearchCriteria is a class that holds the criteria
...
string filter = string.Empty;

if (!string.IsNullOrEmpty(aSearchCriteria.RegistrationNumber)) filter =
        "f.BusinessRegistrationNumber =  " + 
        aSearchCriteria.BusinessRegistrationNumber + " ";
if (aSearchCriteria.ChangedStartDate != null && aSearchCriteria.ChangedEndDate != null)
{
   if (!string.IsNullOrEmpty(filter))
   {
       filter += " && f.ChangedDate >=  " +
                 aSearchCriteria.ChangedStartDate.ToShortDateString()  + 
                          "  && f.ChangedDate <=  " +
                aSearchCriteria.ChangedEndDate.ToShortDateString() + " ";
   }
   else
   {
       ...
   }
}
...

Using (CustomerEntities db = new CustomerEntities())
{
    if (!string.IsNullOrEmpty(filter))
    {
        filter = "f => " + filter;
        **return db.Customers.Where(filter).ToList();**
    }
    else
    ...
 }
 ...

Sample:

 "filter" value: f => f.ChangedDate >  01/01/2012  && f.ChangedDate <  14/01/2012

我执行这一错误信息:

问题不成立。近期;第6行,第5栏。

Answer 1

你不想使过滤器成为一种扼杀。相反,你应当做的是把过滤器应用到你能够得到的治疗。类似:

var customers = db.Customers.AsQueryable();

if (aSearchCriteria.ChangedStartDate != null && aSearchCriteria.ChangedEndDate != null)
{
    customers = customers
        .Where(c => c.ChangedDate >= aSearchCriteria.ChangedStartDate &&
                    c.ChangedDate >= aSearchCriteria.ChangedEndDate);
}

// ... apply other filters as necessary

return customers.ToList();

Answer 2

Assuming you are using ObjectQuery.Where(string) the string predicate should look like

"it.ChangedDate >  01/01/2012  && it.ChangedDate <  14/01/2012 "

(无 f=>表中的其他部分为)

请确认它有助于:

友情链接