私はEF5を使用しており、次のような質問を見つけています:
context.Questions
.OrderBy(x => Guid.NewGuid())
.Where(x => x.Difficulty == difficulty && x.Format == format);
各質問には、分単位の値 (2、4、6、および 8) を持つ期間という名前のフィールドがあります。
次の int 配列があります: { 4, 0, 1, 2 } つまり:
2 分の 4 問、4 分の 0 問、6 分の 1 問、8 分の 2 問を取得します。
.OrderBy と .Where の後、前述の 7 つの質問を取得する必要があります。
すべての質問をロードしたり、4 つのクエリを使用したりせずにこれを行う方法はありますか?
ありがとう、ミゲル
これは一種のハードコーディングされていますが、アイデアが得られ、問題が明示的に解決されます。ここから必要なものに変換できるはずです。
var questions = context.Questions .OrderBy(x => Guid.NewGuid())
.Where(x => x.Difficulty == difficulty && x.Format == format);
var selectedQuestions = questions.Where(q => q.Duration == 2).Take(questionArray[0])
.Union(questions.Where(q => q.Duration == 4).Take(questionArray[1]))
.Union(questions.Where(q => q.Duration == 6).Take(questionArray[2]))
.Union(questions.Where(q => q.Duration == 8).Take(questionArray[3]));
クエリ可能なものを列挙することはないため、EF はこれらすべてのユニオンを sql で実行し、1 回の呼び出しですべてのデータを取得します。
生成された SQL:
SELECT [Distinct3].[C1] AS [C1],
[Distinct3].[C2] AS [C2],
[Distinct3].[C3] AS [C3],
[Distinct3].[C4] AS [C4]
FROM (SELECT DISTINCT [UnionAll3].[C1] AS [C1],
[UnionAll3].[C2] AS [C2],
[UnionAll3].[C3] AS [C3],
[UnionAll3].[C4] AS [C4]
FROM (SELECT [Distinct2].[C1] AS [C1],
[Distinct2].[C2] AS [C2],
[Distinct2].[C3] AS [C3],
[Distinct2].[C4] AS [C4]
FROM (SELECT DISTINCT [UnionAll2].[C1] AS [C1],
[UnionAll2].[C2] AS [C2],
[UnionAll2].[C3] AS [C3],
[UnionAll2].[C4] AS [C4]
FROM (SELECT [Distinct1].[C1] AS [C1],
[Distinct1].[C2] AS [C2],
[Distinct1].[C3] AS [C3],
[Distinct1].[C4] AS [C4]
FROM (SELECT DISTINCT [UnionAll1].[Id] AS [C1],
[UnionAll1].[Duration] AS [C2],
[UnionAll1].[Difficulty] AS [C3],
[UnionAll1].[Format] AS [C4]
FROM (SELECT TOP (4) [Project1].[Id] AS [Id],
[Project1].[Duration] AS [Duration],
[Project1].[Difficulty] AS [Difficulty],
[Project1].[Format] AS [Format]
FROM (SELECT NEWID() AS [C1],
[Extent1].[Id] AS [Id],
[Extent1].[Duration] AS [Duration],
[Extent1].[Difficulty] AS [Difficulty],
[Extent1].[Format] AS [Format]
FROM [dbo].[Questions] AS [Extent1]
WHERE ([Extent1].[Difficulty] = @p__linq__0)
AND ([Extent1].[Format] = @p__linq__1)
AND (2 = [Extent1].[Duration])) AS [Project1]
ORDER BY [Project1].[C1] ASC
UNION ALL
SELECT TOP (0) [Project3].[Id] AS [Id],
[Project3].[Duration] AS [Duration],
[Project3].[Difficulty] AS [Difficulty],
[Project3].[Format] AS [Format]
FROM (SELECT NEWID() AS [C1],
[Extent2].[Id] AS [Id],
[Extent2].[Duration] AS [Duration],
[Extent2].[Difficulty] AS [Difficulty],
[Extent2].[Format] AS [Format]
FROM [dbo].[Questions] AS [Extent2]
WHERE ([Extent2].[Difficulty] = @p__linq__2)
AND ([Extent2].[Format] = @p__linq__3)
AND (4 = [Extent2].[Duration])) AS [Project3]
ORDER BY [Project3].[C1] ASC) AS [UnionAll1]) AS [Distinct1]
UNION ALL
SELECT TOP (1) [Project7].[Id] AS [Id],
[Project7].[Duration] AS [Duration],
[Project7].[Difficulty] AS [Difficulty],
[Project7].[Format] AS [Format]
FROM (SELECT NEWID() AS [C1],
[Extent3].[Id] AS [Id],
[Extent3].[Duration] AS [Duration],
[Extent3].[Difficulty] AS [Difficulty],
[Extent3].[Format] AS [Format]
FROM [dbo].[Questions] AS [Extent3]
WHERE ([Extent3].[Difficulty] = @p__linq__4)
AND ([Extent3].[Format] = @p__linq__5)
AND (6 = [Extent3].[Duration])) AS [Project7]
ORDER BY [Project7].[C1] ASC) AS [UnionAll2]) AS [Distinct2]
UNION ALL
SELECT TOP (2) [Project11].[Id] AS [Id],
[Project11].[Duration] AS [Duration],
[Project11].[Difficulty] AS [Difficulty],
[Project11].[Format] AS [Format]
FROM (SELECT NEWID() AS [C1],
[Extent4].[Id] AS [Id],
[Extent4].[Duration] AS [Duration],
[Extent4].[Difficulty] AS [Difficulty],
[Extent4].[Format] AS [Format]
FROM [dbo].[Questions] AS [Extent4]
WHERE ([Extent4].[Difficulty] = @p__linq__6)
AND ([Extent4].[Format] = @p__linq__7)
AND (8 = [Extent4].[Duration])) AS [Project11]
ORDER BY [Project11].[C1] ASC) AS [UnionAll3]) AS [Distinct3];
各タイプの 4 つ (または配列の最大数) の質問を取得し、クライアントでフィルタリングを実行しないのはなぜですか? 16 の結果があれば、安価なはずです。linq グループ化を使用して分単位でグループ化すると、簡単になります。ここでのもう 1 つの興味深い点は順序付けです... 4 つ以上の質問があり、選択するときに常にそれらを順序付けている場合、最初の 4 つだけの他の質問が表示されることはありますか?