C# Linq 表达式无法翻译

Question

我正在尝试执行 linq 查询来获取所有具有某些特定技能的员工。 search.skills 是具有某些技能的字符串列表，我想检索具有所有这些技能(和条件)的所有用户。在我关于员工的 where 子句中，exp.Skills 是 ICollection，expSkill.SkillName 是技能名称

                .Where(
                emp => search.Skills.All(
                    searchSkill => emp.Experiences.Select(exp => exp.Skills).SelectMany(x => x).Select(expSkill => expSkill.SkillName).Contains(searchSkill)
                ))
            .ToListAsync();

我在尝试执行它时收到以下错误。我正在使用entityframework core 3

The LINQ expression 'DbSet<Employee>
.Where(e => __search_Skills_0
    .All(searchSkill => DbSet<Experience>
        .Where(e0 => EF.Property<Nullable<Guid>>(e, "Id") != null && EF.Property<Nullable<Guid>>(e, "Id") == EF.Property<Nullable<Guid>>(e0, "EmployeeId"))
        .SelectMany(
            source: e0 => DbSet<ExperienceSkill>
                .Where(e1 => EF.Property<Nullable<Guid>>(e0, "EmployeeId") != null && new AnonymousObject(new object[]
                { 
                    (object)EF.Property<Nullable<Guid>>(e0, "EmployeeId"), 
                    (object)EF.Property<string>(e0, "ProjectCode") 
                }) == new AnonymousObject(new object[]
                { 
                    (object)EF.Property<Nullable<Guid>>(e1, "ExperienceEmployeeId"), 
                    (object)EF.Property<string>(e1, "ExperienceProjectCode") 
                })), 
            collectionSelector: (e0, c) => new TransparentIdentifier<Experience, ExperienceSkill>(
                Outer = e0, 
                Inner = c
            ))
        .Select(ti => ti.Inner.SkillName)
        .Contains(searchSkill)))' could not be translated. Either rewrite the query in a form that can be translated, or switch to client evaluation explicitly by inserting a call to either AsEnumerable(), AsAsyncEnumerable(), ToList(), or ToListAsync(). See https://go.microsoft.com/fwlink/?linkid=2101038 for more information.

谁能告诉我我在查询中做错了什么？谢谢

Answer 1

EF Core 目前无法在 search.Skills 等内存集合上转换除简单 Contains 之外的 LINQ 运算符。

因此您需要找到 memoryCollection.All 运算符的替代方案。在这种情况下，我使用的是“计数匹配”方法，该方法查找所有匹配记录并比较不同值的计数。

例如替换

emp => search.Skills.All(
    searchSkill => emp.Experiences.Select(exp => exp.Skills).SelectMany(x => x).Select(expSkill => expSkill.SkillName).Contains(searchSkill)

与

emp => emp.Experiences
    .SelectMany(exp => exp.Skills, (exp, skill) => skill.SkillName)
    .Where(skillName => search.Skills.Contains(skillName))
    .Distinct().Count() == search.Skills.Distinct().Count()