关于.net：C＃LINQ在两个不同的数据集上使用条件where子句连接

C# LINQ join with conditional where clause on two different data sets

我有两个集合要与之比较数据。我可以通过ID加入这两个集合。我需要有一个WHERE子句，它返回集合A中找不到集合B中某些项的数据列表

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public class Contract
{
public string ContractId { get; set; }
public IList InvoiceList { get; set; }

public class Invoice
{
public int InvoiceNumber { get; set; }
}
}

public class PaymentRequest
{
public IList Contracts { get; set; }
public class ContractList
{
public string ContractId { get; set; }
public IList Invoices { get; set; }
}

public class InvoiceList
{
public int InvoiceNumber { get; set; }
}
}

到目前为止，我有以下几点，但还不能完全理解WHERE子句。

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var query = (
from request in (
from contract in paymentRequest.Contracts
from invoice in contract.Invoices
select new { contract, invoice })
join valid in (
from contract in validContracts
select new { contract })
on new { request.contract.ContractId } equals new { valid.contract.ContractId }
where !(
// get a list of invoice numbers in the request data set that are not in the valid data set
)
select"Contract Id:" + request.contract.ContractId +
", Invoice Number:" + request.invoice.InvoiceNumber
).ToList();

感谢您的帮助。

相关讨论

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var collectionAIds = new HashSet<int>(collectionA.Select(colAItem => colAItem.Id));
var itemsInCollectionBNotInCollectionA = collectionB.Where(colBItem =>
!collectionAIds.Contains(colBItem.Id));

基本上，我们要获取集合A中的ID，然后从集合B中选择所有项，而不是A的ID列表中。

哈希集是可选的。如果不使用该变量，它只会避免重复的O(N)查找。

P.S.我假设int是ID的类型。为哈希集使用ID的数据类型。

在我看来，您的查询应该如下所示：

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var query =
(
from request in
(
from contract in paymentRequest.Contracts
from invoice in contract.Invoices
select new { contract, invoice }
)
join valid in
(
from contract in validContracts
select new { contract }
) on new { request.contract.ContractId } equals new { valid.contract.ContractId } into gvs
where
gvs
.SelectMany(gv => gv.contract.Invoices)
.Select(i => i.InvoiceNumber)
.All(n => n != request.invoice.InvoiceNumber)
select"Contract Id:" + request.contract.ContractId +
", Invoice Number:" + request.invoice.InvoiceNumber
).ToList();

与提醒常规SQL查询的功能相比，使用contains会降低性能。这样会更好

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var result =
from itm1 in Coll1
from itm2 in Coll2.Where(x => x.Id == itm1.Id).DefaultIfEmpty()
where itm2 == null
select itm1;

这将为您提供列2中不存在的Coll1中的所有项目。这比任何时候使用contains都快