c# - Entity Framework 中有序集的并集，然后跳过

Question

我有一个类(class)表，我想对其多个字段执行文本搜索。但是，搜索应该按顺序进行:例如类(class)有一个 Keywords 字段和 Description 字段。搜索应优先于通过关键字找到的值。所有内容都应该按日期排序，但只有在考虑优先级之后才可以。

我最后还使用了 https://github.com/troygoode/PagedList 中的 ToPagedList() (我认为它只是使用 Skip() 和 Top() 来管理页面)

这是我到目前为止所拥有的:

string[] word = /*Search words*/
var data = db.LessonsLearneds.Where(dbRecord => words.Any(word =>
        dbRecord.SearchKeywords.StartsWith(word + ",") ||
        dbRecord.SearchKeywords.Contains("," + word + ",") ||
        dbRecord.SearchKeywords.EndsWith("," + word)))
        .Select(x => new { Record = x, Order = 1 });

data = data.Union(
    db.LessonsLearneds
        .Where(dbRecord => words.Any(word => dbRecord.Title.Contains(word)))
        .Select(x => new { Record = x, Order = 2 }));

data = data.Union(
     db.LessonsLearneds
        .Where(dbRecord => words.Any(word => dbRecord.Description.Contains(word)))
        .Select(x => new { Record = x, Order = 3}));

data = data.Union(
     db.LessonsLearneds
        .Where(dbRecord => words.Any(word => dbRecord.Lesson.Contains(word)))
        .Select(x => new { Record = x, Order = 4 }));

return data
            .Distinct()
            .OrderBy(x => x.Order)
            .ThenByDescending(x => x.Record.Date)
            .Select(x => x.Record)
            .ToPagedList(pageNumber, pageSize);

总的来说，除了 Distinct() 之外，这段代码几乎满足了我的要求。这里的每个联合都可以检索相同的记录，因此我可能会多次收到它，并且由于虚拟 Order 字段，Distinct() 不会强制唯一性。我无法将 Distinct 放在 Select(x => x.Record) 之后，因为 ToPagedList(..) 需要对集合进行排序(结果:仅 LINQ to Entities 中的排序输入支持“Skip”方法。 异常(exception))

有什么想法吗？

到目前为止，我有一个:在 Distinct 之后添加 Order 字段，但这意味着我必须将这些 Contains 检查写入两次，我认为这非常丑陋解决方案。

Answer 1

首先，由于您由于 Order 值不同而投影唯一记录，因此请将 Union 运算符替换为 Concat(这是 LINQ相当于 SQL UNION ALL)。

string[] word = /*Search words*/
var data = db.LessonsLearneds.Where(dbRecord => words.Any(word =>
        dbRecord.SearchKeywords.StartsWith(word + ",") ||
        dbRecord.SearchKeywords.Contains("," + word + ",") ||
        dbRecord.SearchKeywords.EndsWith("," + word)))
        .Select(x => new { Record = x, Order = 1 });

data = data.Concat(
    db.LessonsLearneds
        .Where(dbRecord => words.Any(word => dbRecord.Title.Contains(word)))
        .Select(x => new { Record = x, Order = 2 }));

data = data.Concat(
     db.LessonsLearneds
        .Where(dbRecord => words.Any(word => dbRecord.Description.Contains(word)))
        .Select(x => new { Record = x, Order = 3}));

data = data.Concat(
     db.LessonsLearneds
        .Where(dbRecord => words.Any(word => dbRecord.Lesson.Contains(word)))
        .Select(x => new { Record = x, Order = 4 }));

然后将 Distinct 替换为 GroupBy，使用 x.Record 作为键，并为每个值取最小 Order分组，然后按照当前查询中的方式执行其余操作:

return data
     .GroupBy(x => x.Record)
     .Select(g => new { Record = g.Key, Order = g.Min(x => x.Order) })
     .OrderBy(x => x.Order)
     .ThenByDescending(x => x.Record.Date)
     .Select(x => x.Record)
     .ToPagedList(pageNumber, pageSize);