Question

这使我今天无法解决问题。我有这个简单的查询

var result =
    DataContext.Accommodations.Where(a => 
        (criteria.MinPrice == null || a.AccommodationRates.Any(r => r.From >= criteria.MinPrice)) &&
        (criteria.MaxPrice == null || a.AccommodationRates.Any(r => r.To <= criteria.MaxPrice)) &&
        (criteria.Locations == null || criteria.Locations.Count == 0 || a.AccommodationPlaceJoins.Any(j => criteria.Locations.Contains(j.Place.PlaceName)))
);

此查询的最后一行导致我出现问题

(criteria.Locations == null ||
 criteria.Locations.Count == 0 ||
 a.AccommodationPlaceJoins.Any(j => criteria.Locations.Contains(j.Place.PlaceName)))

它给出的错误是

无法创建类型的常量值 'System.Collections.Generic.IList`1'。只有原始类型（'如在此上下文中支持Int32，String和Guid'。

我甚至没有尝试创建列表。我在这里尝试做的就是带回与一个地方相关的住宿（Place表中通过AccommodationPlaceJoin表链接到住宿表的地名）等于标准中的任何一个地名.Locations（属于IList类型）。

我已尝试将此行更改为此行，但它无效。

(criteria.Locations == null ||
 criteria.Locations.Count == 0 ||
 a.AccommodationPlaceJoins.Any(j => criteria.Locations.Any(l => l == j.Place.PlaceName)))

Answer 1

对于null，比较criteria.Locations == null的常量值EF无法创建var result = DataContext.Accommodations.Where(a => (criteria.MinPrice == null || a.AccommodationRates.Any(r => r.From >= criteria.MinPrice)) && (criteria.MaxPrice == null || a.AccommodationRates.Any(r => r.To <= criteria.MaxPrice))); if (criteria.Locations != null && criteria.Locations.Count > 0) { result = result.Where(a => a.AccommodationPlaceJoins .Any(j => criteria.Locations.Contains(j.Place.PlaceName))); }。您需要将查询拆分为两种情况，并检查查询外的空列表，例如：

IQueryable<Accommodation> result = DataContext.Accommodations;

if (criteria.MinPrice != null)
    result = result.Where(a => a.AccommodationRates
        .Any(r => r.From >= criteria.MinPrice));

if (criteria.MaxPrice != null)
    result = result.Where(a => a.AccommodationRates
        .Any(r => r.To <= criteria.MaxPrice));

if (criteria.Locations != null && criteria.Locations.Count > 0)
    result = result.Where(a => a.AccommodationPlaceJoins
        .Any(j => criteria.Locations.Contains(j.Place.PlaceName)));

修改

BTW：在我看来，编写整个查询会使其更易读，并且会简化必须发送到数据库的SQL：

{{1}}

实体框架：无法创建类型为'System.Collections.Generic.IList`1'的常量值

1 个答案: