LINQ to SQL - WHERE 子句过滤

Question

为什么 where 条件没有应用在下面的代码中？当我搜索时，结果没有被过滤。当我调试时，searchString 确实有一个值并且执行是通过 _data.Where 子句进行的，但它没有返回过滤后的结果。

我哪里做错了？

IQueryable<UserViewModel> _data = (
    from a in context.aspnet_Users
    join b in context.aspnet_Membership on a.UserId equals b.UserId
    where b.IsApproved == true
    select new UserViewModel
    {                                 
        UserId = a.UserId,
        UserName = a.UserName,
        FirstName = a.FirstName,
        LastName = a.LastName,
        EmailAddress = b.Email                                 
    })
    .OrderBy(a => a.FirstName)
    .ThenBy(b => b.LastName);

if (!String.IsNullOrEmpty(searchString))
{                  
   _data = _data
        .Where(x => x.FirstName.Contains(searchString))
        .Where(y => y.UserName.Contains(searchString))
        .Where(y => y.LastName.Contains(searchString))
        .Where(y => y.EmailAddress.Contains(searchString));
}

Answer 1

第二个查询的编写方式检查所有过滤字段以搜索字符串开头的记录，即对于 FirstName and[=19= 的用户] LastName and UserName and Email 都以相同的字符串开头。

我认为您想要的是检查这些字段是否以搜索字符串开头的查询，例如：

_data = _data.Where(x => x.FirstName.Contains(searchString) || x.UserName.Contains(searchString) || x.LastName.Contains(searchString) || x.EmailAddress.Contains(searchString));

Answer 2

我怀疑这 "filtering" 比您预期的要多得多：

_data = _data.Where(x => x.FirstName.Contains(searchString))
             .Where(y => y.UserName.Contains(searchString))
             .Where(y => y.LastName.Contains(searchString))
             .Where(y => y.EmailAddress.Contains(searchString));

这要求 searchString 存在于 所有四个 字段中。因此，如果您搜索 "David" 那么它将无法找到我的记录，因为我的 LastName 不包含该字符串。

也许您想使用逻辑 or 而不是逻辑 and？像这样：

_data = _data.Where(x => x.FirstName.Contains(searchString) ||
                         x.UserName.Contains(searchString) ||
                         x.LastName.Contains(searchString) ||
                         x.EmailAddress.Contains(searchString));

LINQ to SQL - WHERE 子句过滤

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