将 SQL 查询转换为 LINQ 查询

Question

这是需要转换为 LINQ 查询的 SQL 查询。

SELECT  pq.DocumentQueueID, 
    pq.DocumentQueueName, 
    pq.DepartmentName, 
    pq.UserLocation,
    ISNULL(T.DocumentCount, 0) DocCount, 
    ISNULL(CONVERT(VARCHAR(50),T.OldestDocumentDate),'') IngestionDateTime,
    ISNULL(B.UserName, '') UserName
FROM [dbo].[listPLDQueues] pq 
LEFT OUTER JOIN 
(
    SELECT dds.CurrentDocumentQueue, 
    SUM(dds.ImportPageCount) as DocumentCount, 
    MIN(dds.IngestionDateTime) as OldestDocumentDate
    FROM [dbo].[dataDocumentStats] dds
    GROUP BY dds.CurrentDocumentQueue
) AS T ON T.CurrentDocumentQueue = pq.DocumentQueueID
LEFT OUTER JOIN
(   SELECT duq.DocumentQueueID, UserName = 
    STUFF((SELECT ', ' + uq.UserDisplayName
    FROM [dbo].[dataUserQueues] uq
    WHERE uq.DocumentQueueID = duq.DocumentQueueID
    FOR XML PATH('')),1,2,'')
 FROM [dbo].[dataUserQueues] duq
 GROUP BY duq.DocumentQueueID
 ) AS B ON B.DocumentQueueID = pq.DocumentQueueID 
WHERE UPPER(WorkflowType) = 'INDEXING'

到目前为止我在 LINQ 查询中做了什么..

 var indexSummary = _eimStatsDB.listPLDQueues
          .Join(_eimStatsDB.dataDocumentStats,
              pld => pld.DocumentQueueID,
              dds => dds.CurrentDocumentQueue,
              (pld, dds) => new { pldQueues = pld, dataDocument = dds })            
          .Where(a => a.pldQueues.WorkflowType.ToLower() == "indexing")
          .GroupBy(a => a.pldQueues.DocumentQueueID)
          .ToList()
          .Select(a => new
          {
              DocumentQueueId = a.Key,
              DocumentQueueName = a.Select(i => i.pldQueues.DocumentQueueName).FirstOrDefault(),
              DepartmentName = a.Select(i => i.pldQueues.DepartmentName).FirstOrDefault(),
              DocumentCount = a.Sum(i => i.dataDocument.ImportPageCount),
              OldestDocumentDate = a.Min(i => i.dataDocument.IngestionDateTime),
              UserLocation = a.Select(i => i.pldQueues.UserLocation).FirstOrDefault(),
              IsChecked = false
          });

        var userNames = _eimStatsDB.dataUserQueues
            .GroupBy(e => e.DocumentQueueID)
            .ToList()
            .Select(e => new
            {
                DocumentId = e.Key,
                UserName = string.Join(",", e.Select(i => i.UserDisplayName))
            });

        var listPLDQueue = from pldqueue in _eimStatsDB.listPLDQueues
                           where pldqueue.WorkflowType == "Indexing"
                           select pldqueue;

        var result = from pldqueue in listPLDQueue
                     join iS in indexSummary
                     on pldqueue.DocumentQueueID equals iS.DocumentQueueId into pldjoin
                     from pld in pldjoin.DefaultIfEmpty()
                     join un in userNames
                     on pld.DocumentQueueId equals un.DocumentId into gj
                     from subuser in gj.DefaultIfEmpty()
                     select new
                     {
                         DocumentQueueId = pld.DocumentQueueId,
                         DocumentQueueName = pld.DocumentQueueName,
                         DepartmentName = pld.DepartmentName,
                         DocumentCount = (pld.DocumentCount == null ? 0 : pld.DocumentCount),
                         OldestDocumentDate = (pld.OldestDocumentDate == null? Convert.ToDateTime(string.Empty) : pld.OldestDocumentDate),
                         UserLocation = pld.UserLocation,
                         IsChecked = pld.IsChecked,
                         Usernames = (subuser == null ? string.Empty : subuser.UserName)
                     };

returns 结果给出错误的最后一个查询： "Unable to create a constant value of type 'Anonymous type'. Only primitive types or enumeration types are supported in this context."

是否有任何其他更好的方法可以将所有不同的 LINQ 查询组合在一起？

Answer 1

检查整个查询结构后，我发现除了 listPLDQueue 之外的另外两个 join 来源是 IEnumerable 具有匿名类型参数的集合，其中 Entity Framework 只能引用 IEnumerable 以原始类型作为类型参数或 IQueryable 执行连接操作时。

尝试删除或评论所有 ToList() 方法，为 indexSummary 和 userNames 分配 IQueryable，然后考虑使用适当的 class 名称而不是使用匿名像这样输入：

var indexSummary = _eimStatsDB.listPLDQueues
          .Join(_eimStatsDB.dataDocumentStats,
              pld => pld.DocumentQueueID,
              dds => dds.CurrentDocumentQueue,
              (pld, dds) => new { pldQueues = pld, dataDocument = dds })            
          .Where(a => a.pldQueues.WorkflowType.ToLower() == "indexing")
          .GroupBy(a => a.pldQueues.DocumentQueueID)
        //.ToList() --> this converts IQueryable to IEnumerable, which should be dropped
          .Select(a => new listPLDQueues() // change this assignment to your model class name
          {
              DocumentQueueId = a.Key,
              DocumentQueueName = a.Select(i => i.pldQueues.DocumentQueueName).FirstOrDefault(),
              DepartmentName = a.Select(i => i.pldQueues.DepartmentName).FirstOrDefault(),
              DocumentCount = a.Sum(i => i.dataDocument.ImportPageCount),
              OldestDocumentDate = a.Min(i => i.dataDocument.IngestionDateTime),
              UserLocation = a.Select(i => i.pldQueues.UserLocation).FirstOrDefault(),
              IsChecked = false
          });

var userNames = _eimStatsDB.dataUserQueues
            .GroupBy(e => e.DocumentQueueID)
          //.ToList() --> this converts IQueryable to IEnumerable, which should be dropped
            .Select(e => new dataUserQueues() // change this assignment to your model class name
            {
                DocumentId = e.Key,
                UserName = string.Join(",", e.Select(i => i.UserDisplayName))
            });

每个赋值都会return IQueryable<T>（T被赋值给数据库模型class名称，即IQueryable<listPLDQueues>和IQueryable<dataUserQueues>）哪个适合使用它们在包含 join 查询的 result 作业中。

将 SQL 查询转换为 LINQ 查询

Converting SQL query to LINQ query

c#

linq

sql-server

linq-to-entities

entity-framework