EF4 添加 is null 子句到 where 子句

Question

我有以下 linq 查询：

var fileDocuments = (
    from doc in fileUploads
    from invoice in
        (
            from inv in _dbContext.SupplierInvoiceHeaders
            where inv.InvoiceDocumentId == doc.ID || inv.JobSheetInvoiceId == doc.ID
            select inv
            ).DefaultIfEmpty()
    join pos in _dbContext.PurchaseOrders on invoice.PurchaseOrder.PurchaseOrderId equals pos.PurchaseOrderId into poss
    from po in poss.DefaultIfEmpty()
    join hdf in _dbContext.HelpDeskFaults on po.HelpdeskFaultId equals hdf.ID into hdfpo
    from hs in hdfpo.DefaultIfEmpty()
    join store1 in _dbContext.Stores on hs.StoreID equals store1.ID into hsf
    from hdfStore in hsf.DefaultIfEmpty()
    join js in _dbContext.JobSheets on invoice.SupplierInvoiceHeaderId equals js.SupplierInvoiceHeaderID into jss
    from jobSheets in jss.DefaultIfEmpty()
    join ch in _dbContext.ChildProjects on po.ChildProjectId equals ch.ID into chs
    from childProjects in chs.DefaultIfEmpty()
    join ph in _dbContext.ProjectHeaders on childProjects.ProjectHeaderID equals ph.ID into phs
    from projectHeaders in phs.DefaultIfEmpty()
    join ppmsl in _dbContext.PpmScheduleLines on projectHeaders.PPMScheduleRef equals ppmsl.ID into ppsmsls
    from ppmScheduleLines in ppsmsls.DefaultIfEmpty()
    join ss2 in _dbContext.Stores on ppmScheduleLines.StoreID equals ss2.ID into ssts
    from store2 in ssts.DefaultIfEmpty()
    select new
    {
        doc.ID,
        JobSheetId = jobSheets.DocumentID,
        doc.Name,
        doc.DateCreated,
        doc.StoreID,
        StoreName = doc.Store.Name,
        DocumentType = doc.DocumentType.Name,
        doc.DocumentTypeID,
        HelpDeskFaultStoreName = hs.Store.Name,
        DocStoreName = doc.Store.Name,
        PPMScheduleLinesStoreName = ppmScheduleLines.Store.Name,
        PIR = invoice.PurchaseInvoiceReference
    });


    fileDocuments = fileDocuments.Where(x => x.PIR == jobSearchParams.PIR);

生成的 where 子句如下所示：

WHERE ([Extent2].[fld_str_PIR] = @p__linq__0) OR (([Extent2].[fld_str_PIR] IS NULL) AND (@p__linq__0 IS NULL))

我不明白为什么要添加 IS NULL 子句。

Answer 1

添加它们是因为您的 jobSearchParams.PIR 可能为空。如果它为空，EF 将假定您想要 return 行，其中 fld_str_PIR 为空。但在 sql 中，您无法使用“=”运算符与 null 进行比较：

WHERE ([Extent2].[fld_str_PIR] = @p__linq__0) -- doesn't work if @p__linq__0 is null

这就是它为您处理这种情况并为两种情况生成正确查询的原因 - 无论 jobSearchParams.PIR 是否为 null。

Answer 2

经过大量搜索，我发现另一个 post 突出显示了 UseDatabaseNullSemantics 设置：

context.Configuration.UseDatabaseNullSemantics = true;

启用此设置后，我的查询将在 900 毫秒内运行而不是超时。

EF4 添加 is null 子句到 where 子句

EF4 adding is null clause onto where clause

c#

entity-framework

entity-framework-4