Linq到实体-一对多关系-需要左外部联接而不是交叉联接 [英] Linq to entities - One to many relationship - need left outer join instead of cross join
问题描述
我有以下模型:
我需要特定用户的所有固定装置和预测(如果该固定装置具有预测)的列表.返回我需要的sql如下:
I need a list of all fixtures and predictions (if that fixture has a prediction) for a specific user. The sql to return what I need is as follows:
SELECT * FROM Fixture f
LEFT OUTER JOIN Prediction p ON f.FixtureId = p.FixtureId
WHERE p.UserID = '06E4D3E0-8365-45BF-9054-3F8534C7AD5E' OR p.UserID IS NULL
我尝试过:
var query = from f in c.Fixtures
from p in c.Predictions.Where(pre => pre.UserId == new Guid("06E4D3E0-8365-45BF-9054-3F8534C7AD5E") || pre.UserId == null)
select new
{
FixtureId = f.FixtureId,
HomeScore = f.HomeTeamScore,
AwayScore = f.AwayTeamScore,
PredictionId = p.PredictionId,
HomePrediction = p.HomeTeamPrediction,
AwayPrediction = p.AwayTeamPrediction
};
但这会生成(并给出错误的结果):
But that generates (and gives the wrong results):
SELECT
[Extent1].[FixtureId] AS [FixtureId],
[Extent1].[HomeTeamScore] AS [HomeTeamScore],
[Extent1].[AwayTeamScore] AS [AwayTeamScore],
[Extent2].[PredictionId] AS [PredictionId],
[Extent2].[HomeTeamPrediction] AS [HomeTeamPrediction],
[Extent2].[AwayTeamPrediction] AS [AwayTeamPrediction]
FROM [dbo].[Fixture] AS [Extent1]
CROSS JOIN [dbo].[Prediction] AS [Extent2]
WHERE cast('06e4d3e0-8365-45bf-9054-3f8534c7ad5e' as uniqueidentifier) = [Extent2].[UserId]
将DefaultIfEmpty
添加到第二个"from"中,例如:
Adding DefaultIfEmpty
to the second 'from' like:
var query = from f in c.Fixtures
from p in c.Predictions.Where(pre => pre.UserId == new Guid("06E4D3E0-8365-45BF-9054-3F8534C7AD5E") || pre.UserId == null).DefaultIfEmpty()
select new
{
FixtureId = f.FixtureId,
HomeScore = f.HomeTeamScore,
AwayScore = f.AwayTeamScore,
PredictionId = p.PredictionId,
HomePrediction = p.HomeTeamPrediction,
AwayPrediction = p.AwayTeamPrediction
};
生成(并且仍然给出错误的结果):
Generates (and still gives the wrong results):
SELECT
[Extent1].[FixtureId] AS [FixtureId],
[Extent1].[HomeTeamScore] AS [HomeTeamScore],
[Extent1].[AwayTeamScore] AS [AwayTeamScore],
[Join1].[PredictionId] AS [PredictionId],
[Join1].[HomeTeamPrediction] AS [HomeTeamPrediction],
[Join1].[AwayTeamPrediction] AS [AwayTeamPrediction]
FROM [dbo].[Fixture] AS [Extent1]
CROSS JOIN (SELECT [Project1].[PredictionId] AS [PredictionId], [Project1].[HomeTeamPrediction] AS [HomeTeamPrediction], [Project1].[AwayTeamPrediction] AS [AwayTeamPrediction]
FROM ( SELECT 1 AS X ) AS [SingleRowTable1]
LEFT OUTER JOIN (SELECT
[Extent2].[PredictionId] AS [PredictionId],
[Extent2].[UserId] AS [UserId],
[Extent2].[HomeTeamPrediction] AS [HomeTeamPrediction],
[Extent2].[AwayTeamPrediction] AS [AwayTeamPrediction]
FROM [dbo].[Prediction] AS [Extent2]
WHERE cast('06e4d3e0-8365-45bf-9054-3f8534c7ad5e' as uniqueidentifier) = [Extent2].[UserId] ) AS [Project1] ON 1 = 1 ) AS [Join1]
按原样使用现有关系(这是我要出问题的地方,请参见下面的答案):
Using the existing relationship as-is like (this was where I was going wrong, see answer below):
var query = from f in c.Fixtures
from p in c.Predictions
where c.Predictions.Any(pre => pre.UserId == new Guid("06E4D3E0-8365-45BF-9054-3F8534C7AD5E") || pre.UserId == null)
select new
{
FixtureId = f.FixtureId,
HomeScore = f.HomeTeamScore,
AwayScore = f.AwayTeamScore,
PredictionId = p.PredictionId,
HomePrediction = p.HomeTeamPrediction,
AwayPrediction = p.AwayTeamPrediction
};
生成:
SELECT
[Extent1].[FixtureId] AS [FixtureId],
[Extent1].[HomeTeamScore] AS [HomeTeamScore],
[Extent1].[AwayTeamScore] AS [AwayTeamScore],
[Extent2].[PredictionId] AS [PredictionId],
[Extent2].[HomeTeamPrediction] AS [HomeTeamPrediction],
[Extent2].[AwayTeamPrediction] AS [AwayTeamPrediction]
FROM [dbo].[Fixture] AS [Extent1]
CROSS JOIN [dbo].[Prediction] AS [Extent2]
WHERE EXISTS (SELECT
1 AS [C1]
FROM [dbo].[Prediction] AS [Extent3]
WHERE cast('06e4d3e0-8365-45bf-9054-3f8534c7ad5e' as uniqueidentifier) = [Extent3].[UserId]
)
如何生成我需要的查询?
How do generate the query I need?
推荐答案
EF为您生成了导航属性,请继续使用它们!
EF has generated navigation properties for you, so go ahead and use them!
代替
var query =
from f in c.Fixtures
from p in c.Predictions
.Where(pre => pre.UserId == new Guid("06E4D3E0-8365-45BF-9054-3F8534C7AD5E")
|| pre.UserId == null)
尝试
var query =
from f in c.Fixtures
from p in f.Predictions
.Where(pre => pre.UserId == new Guid("06E4D3E0-8365-45BF-9054-3F8534C7AD5E")
|| pre.UserId == null)
请注意,使用join
和DefaultIfEmpty
通常是一个错误EF .
Note that using join
and DefaultIfEmpty
is often a mistake in EF.
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