使用 Linq 在 EF-Core 中进行 INNER Join 和 LEFT OUTER JOIN答案

【问题标题】：INNER Join and LEFT OUTER JOIN in EF-Core with Linq使用 Linq 在 EF-Core 中进行 INNER Join 和 LEFT OUTER JOIN
【发布时间】：2019-07-23 13:34:51
【问题描述】：

我正在尝试将以下 SQL 转换为 c# 中的 Linq 查询（.net core 2.1 和 EF core 2.2）

SELECT  TD.*, RD.Match
        FROM    TransactionDetail TD
                INNER JOIN dbo.Measure M ON M.InternalID = TD.MetricCode
                LEFT OUTER JOIN (
                    SELECT tmp.ID, tmp.ReportingDate, 1 AS Match
                    FROM tmp
                ) AS RD ON RD.ID = M.Frequency AND RD.ReportingDate = TD.ReportingDate
        WHERE   RD.Match IS NULL AND
                TD.BatchID = @batchID AND
                NOT EXISTS (SELECT TransactionFailureReasonID FROM TransactionDetailFailureReasons R WHERE R.TransactionDetailID = TD.ID and R.TransactionFailureReasonID = 'NRD') AND
                NOT EXISTS (SELECT TransactionFailureReasonID FROM TransactionDetailFailureReasons R WHERE R.TransactionDetailID = TD.ID and R.TransactionFailureReasonID = 'RDP') AND
                NOT EXISTS (SELECT TransactionFailureReasonID FROM TransactionDetailFailureReasons R WHERE R.TransactionDetailID = TD.ID and R.TransactionFailureReasonID = 'RDF')

有人可以帮助我如何先进行内部联接，然后再进行左外部联接吗？

我已经走了这么远，

var IQ1 = (from TD in IngestionHubContext.TransactionDetail
                   join M in  ModelHospitalPreviewContext.Measure on TD.MetricCode equals M.InternalId 
                   join R in RD.DefaultIfEmpty on new {ID = M.Frequency, TD.ReportingDate} equals new { R.ID, R.ReportingDate} into J
                   //?????

感谢任何帮助或建议。

提前致谢。

【问题讨论】：

标签： c# sql linq .net-core entity-framework-core

【解决方案1】：

您可以在下面找到示例的简化版本，使用单个 DbContext：

var batchId = 123;

var transactionDetailFailureReasonsToExcludeQuery =
    from r in dbContext.TransactionDetailFailureReasons
    where
        r.TransactionFailureReasonID == "NRD" ||
        r.TransactionFailureReasonID == "RDP" ||
        r.TransactionFailureReasonID == "RDF"
    select r.TransactionDetailID;

var query =
    from td in dbContext.TransactionDetail
    join m in dbContext.Measure on td.MetricCode equals m.InternalID
    join rd in dbContext.Tmp on new { m.Frequency, td.ReportingDate } equals new { Frequency = rd.ID, rd.ReportingDate } into rdItems
    from rd in rdItems.DefaultIfEmpty()
    where
        rd == null &&
        td.BatchID == batchId &&
        transactionDetailFailureReasonsToExcludeQuery.Contains(td.ID) == false
    select td;

现在您需要对其进行更新，以便为实体使用正确的DbContext。

希望这会有所帮助。

【讨论】：

@PUBG - 你的TransactionDetail 类是否有TransactionDetailFailureReasons 的导航属性？这个答案似乎做了你想做的事（而不是回避它），但如果你有一个导航属性，失败原因测试可能会更自然。

【解决方案2】：

在 Ef Core 中，您可以使用 SQL 查询，而不必将它们更改为 Linq 查询。目前，Ef Core 不支持将所有 Linq 操作转换为 SQL。因此，将 SQL 转换为 Linq 可能会导致 client-side evaluation。

您可以在这里找到详细信息：Raw SQL

请使用您的模型值更改您的 Select 查询。

var transactionDetails = IngestionHubContext.TransactionDetail.FromSql("SELECT  TD.*, RD.Match
        FROM    TransactionDetail TD
                INNER JOIN dbo.Measure M ON M.InternalID = TD.MetricCode
                LEFT OUTER JOIN (
                    SELECT tmp.ID, tmp.ReportingDate, 1 AS Match
                    FROM tmp
                ) AS RD ON RD.ID = M.Frequency AND RD.ReportingDate = TD.ReportingDate
        WHERE   RD.Match IS NULL AND
                TD.BatchID = @batchID AND
                NOT EXISTS (SELECT TransactionFailureReasonID FROM TransactionDetailFailureReasons R WHERE R.TransactionDetailID = TD.ID and R.TransactionFailureReasonID = 'NRD') AND
                NOT EXISTS (SELECT TransactionFailureReasonID FROM TransactionDetailFailureReasons R WHERE R.TransactionDetailID = TD.ID and R.TransactionFailureReasonID = 'RDP') AND
                NOT EXISTS (SELECT TransactionFailureReasonID FROM TransactionDetailFailureReasons R WHERE R.TransactionDetailID = TD.ID and R.TransactionFailureReasonID = 'RDF')", batchIDParameter);

我希望这会有所帮助。

【讨论】：