不能比较类型的元素'System.Collections.Generic.ICollection`1只有基本类型，枚举类型和实体类型的支持

问题描述

我写了这个代码

        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();

不过在了ToList行我得到异常

However at the ToList line I am getting the exception

{不能比较类型的元素'System.Collections.Generic.ICollection`1 [PROJECT1，版本= 1.0.0.0，文化=中立，公钥=空]]'。只有基本类型，枚举类型和实体类型都支持。}

{"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

您不能将相关的表比较空直接。相反，比较对你的外键成员（假设 PrimaryTable 参考 RelatedTable 使用名为成员 。s.RelatedTableId = NULL&安培;！&放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"));

您甚至可以用完全删除空检查就完事了。因为这个查询对数据库运行，你不会得到一个的NullReferenceException ，它可能工作。你必须仔细检查上，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.

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