无法比较类型“System.Collections.Generic.ICollection”的元素1只支持基本类型，枚举类型和实体类型 [英] Cannot compare elements of type 'System.Collections.Generic.ICollection`1 Only primitive types, enumeration types and entity types are supported

问题描述

我写了这段代码

IQueryable<Site> sites = context.MainTable.Include("RelatedTable");

if (!string.IsNullOrEmpty(param1)) {
    sites = sites.Where(s => s.RelatedTable != null && s.RelatedTable.Any(p => p.Name == param1.ToLower() && p.PolicyType == "primary"));
}

foreach (string secondaryPolicy in secondaryPolicies)
{
    sites = sites.Where(s => s.RelatedTable != null && s.RelatedTable.Any(p => p.Name == secondaryPolicy.ToLower() && p.PolicyType == "secondary"));
}

return sites.ToList();

然而在 ToList 例外

无法比较类型为
'System.Collections.Generic.ICollection`1的元素[[Project1，Version = 1.0 .0.0，
Culture = neutral，PublicKeyToken = null]]'。只支持基本类型
枚举类型和实体类型。

Cannot compare elements of type 'System.Collections.Generic.ICollection`1[[Project1, Version=1.0.0.0, Culture=neutral, PublicKeyToken=null]]'. Only primitive types, enumeration types and entity types are supported.

推荐答案

你无法直接将相关表与 null 进行比较。相反，与您的外键成员进行比较（假设 PrimaryTable 参考 RelatedTable 使用一个名为 RelatedTableId 。

You can't compare a related table to null directly. Instead, compare against your foreign key member (assuming that PrimaryTable reference RelatedTable using a member called RelatedTableId.

sites.Where(s => s.RelatedTableId != null && s.RelatedTable.Any(
    p => p.Name == param1.ToLower() && p.PolicyType == "primary"));

甚至可以完全删除空检查，因为这个查询是针对数据库运行的，所以你不会得到一个 NullReferenceException 它可能会工作，你必须仔细检查，虽然。

You may even be able to get away with removing the null check completely. Since this query is run against the database, you won't get a NullReferenceException and it may work. You'll have to double check on that though.

这篇关于无法比较类型“System.Collections.Generic.ICollection”的元素1只支持基本类型，枚举类型和实体类型的文章就介绍到这了，希望我们推荐的答案对大家有所帮助，也希望大家多多支持IT屋！