c# - 在 Parallel.ForEach : The underlying provider failed on Open. 与 EF5

Question

此代码有时适用于某些项目，但在尝试处理更多项目时总是失败，我会得到这个:{"The underlying provider failed on Open." exception

  List<Recon> scenarioAll = db.Transactions
                  .Where(t => t.SrcObjTyp == "13")
                  .Select(t => t.Recon).ToList();


  //db.Transactions.Where(t => t.SrcObjTyp == "13").ToList().ForEach(t => reconsWithType13Trans.Add(t.Recon));

  Parallel.ForEach(scenarioAll.Take(100), r =>
  {

    // ### Exception : {"The underlying provider failed on Open."} here ###
    invoices = r.Transactions.SelectMany(t => t.InvoiceDetails).ToList();


    CreateFacts(invoices, r/*, db*/).ForEach(f => facts.Add(f));
    transactions = r.Transactions.Where(t => !t.SrcObjTyp.Contains("13")).ToList();
    DistributeTransactionOnItemCode(transactions, facts);
    Console.WriteLine(i += 1);
  });

  facts.ForEach(f => db.ReconFacts.Add(f));
  db.SaveChanges();

我认为问题是多个进程同时访问数据库是否可以让 EF 以这种方式被多个进程查询？

还有一种方法可以将所有内容加载到内存中，因此当像这样访问 Recon 的子项时 r.Transactions.SelectMany(t => t.InvoiceDetails).ToList(); 一切都在内存中而不访问底层数据库？

我应该使用什么解决方案，您认为最好的是什么？

Answer 1

您的问题是您有多个线程尝试延迟加载。尝试将您的负载查询替换为...

List<Recon> scenarioAll = db.Transactions
              .Where(t => t.SrcObjTyp == "13")
              .Select(t => t.Recon)
              .Include(r => r.Transactions.Select(t => t.InvoiceDetails))
              .ToList();

http://msdn.microsoft.com/en-us/library/gg671236(v=vs.103).aspx

一般来说，如果您依赖延迟加载，那您就错了。

或者，假设您可能不需要事务...您可以这样做...

 var query =  = db.Transactions
              .Where(t => t.SrcObjTyp == "13")
              .Select(t => t.Recon);
 var scenarioAll = query.ToList();
 var invoicesByReconIdQuery = from r in query
                              from t in r.Transactions
                              from i in t.InvoiceDetails
                              group i by r.Id into g
                              select new { Id = g.Key, Invoices = g.ToList() };


 var invoicesByReconId = invoicesByReconIdQuery.ToDictionary(x => x.Id, x => x.Invoices);

 Parallel.ForEach(scenarioAll.Take(100), r =>
 {

     // ### Exception : {"The underlying provider failed on Open."} here ###
     var invoices = invoicesByReconId[r.Id];
 }