EF Core表達式正在本地評估...為什么？

Question

我在數據庫上下文中有一個看起來像這樣的方法：

    public override async Task<IEnumerable<FeedMessage>> GetLatestFeeds(
        int userId,
        int groupId,
        int maxResults = 15,
        long lastId = 0)
    {
        if (lastId == 0) lastId = long.MaxValue;

        var userSpecific = 
            FeedMessages.Where(fm =>
                fm.UserId.HasValue && fm.UserId.Value == userId && fm.Id < lastId && !fm.IsDeleted);

        var groupSpecific = 
            FeedMessages.Where(fm =>
                fm.UserId == null && fm.GroupId.HasValue && fm.GroupId.Value == groupId && fm.Id < lastId && !fm.IsDeleted);

        var siteWide = 
            FeedMessages.Where(fm =>
                fm.UserId == null && fm.GroupId == null && fm.Id < lastId && !fm.IsDeleted);

        var feeds = await
            userSpecific.Union(groupSpecific).Union(siteWide)
                .OrderByDescending(x => x.Id)
                .Take(maxResults)
                .ToListAsync();

        return feeds.OrderBy(x => x.Id);
    }

這里的想法是，我想獲取特定於用戶，特定於組或通用的記錄，按ID進行組織，然后返回前X個結果。

如果運行此命令，則會出現一整屏錯誤：

warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Union({from FeedMessage fm in value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MySolution.Common.Entities.FeedMessage]) where ((((([fm].UserId == null) AndAlso ([fm].GroupId != null)) AndAlso (Convert([fm].GroupId, Int32) == __groupId_2)) AndAlso ([fm].Id < __lastId_3)) AndAlso Not([fm].IsDeleted)) select [fm]})' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Union({from FeedMessage fm in value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MySolution.Common.Entities.FeedMessage]) where (((([fm].UserId == null) AndAlso ([fm].GroupId == null)) AndAlso ([fm].Id < __lastId_4)) AndAlso Not([fm].IsDeleted)) select [fm]})' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Union({from FeedMessage fm in value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MySolution.Common.Entities.FeedMessage]) where ((((([fm].UserId == null) AndAlso ([fm].GroupId != null)) AndAlso (Convert([fm].GroupId, Int32) == __groupId_2)) AndAlso ([fm].Id < __lastId_3)) AndAlso Not([fm].IsDeleted)) select [fm]})' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Union({from FeedMessage fm in value(Microsoft.EntityFrameworkCore.Query.Internal.EntityQueryable`1[MySolution.Common.Entities.FeedMessage]) where (((([fm].UserId == null) AndAlso ([fm].GroupId == null)) AndAlso ([fm].Id < __lastId_4)) AndAlso Not([fm].IsDeleted)) select [fm]})' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'orderby [x].Id desc' could not be translated and will be evaluated locally.
warn: Microsoft.EntityFrameworkCore.Query[20500]
      The LINQ expression 'Take(__p_5)' could not be translated and will be evaluated locally.

這里發生了什么？ 我該如何解決？ 這將是一張大表，在本地進行評估會破壞系統。

Answer 1

我最終在EF Core的github網站上發布了一個錯誤報告 ，幾個小時后，我得到了可以使用的響應。 事實證明，服務器端操作尚不支持Union() ， Concat() ， Except()和Intersect() 。 :\\

在我的網絡搜索中，這並不是立即可見的。

根據開發團隊的建議，我可以這樣重寫查詢：

return FeedMessages
    .Where(fm => fm.Id < lastId && !fm.IsDeleted && (
        (fm.UserId.HasValue && fm.UserId.Value == userId) ||
        (fm.UserId == null && fm.GroupId.HasValue && fm.GroupId.Value == groupId) ||
        (fm.UserId == null && fm.GroupId == null)))
    .OrderByDescending(x => x.Id)
    .Take(maxResults)
    .OrderBy(x => x.Id)
    .ToListAsync();

...這使我脫離了危機模式，但我想拋給所有EF Core開發人員，看看這些帖子，這是重要的功能，應盡快在現實中優先考慮（IMO）。