C＃LINQ选择多个 [英] C# LINQ Select Many

问题描述

我匹配病例对照，基本都在案例列表记录，需要有字符串中指定匹配的数量 m_ctrlno 。

到目前为止，我有两个列表，where子句是正确的，但我不能确定如何使用的SelectMany 获得3控制1相匹配情况。我决定使用。取（）功能，但它似乎并不奏效。我没有得到相同的情况下，有3种不同的控制，当我循环的变种查询。

下面是code：

 名单，其中，CaseSelection＆GT; CurrentCaseList =新的名单，其中，CaseSelection＆GT;（）;
的foreach（CaseSelection CurrentCase在m_casesarraylist）
CurrentCaseList.Add（CurrentCase）;

名单＆LT; ControlSelection＆GT; CurrentControlList =新的名单，其中，ControlSelection＆GT;（）;
的foreach（ControlSelection CurrentControlRec在ControlList）
CurrentControlList.Add（CurrentControlRec）;


VAR的查询= CurrentCaseList.SelectMany（
C =＆GT; CurrentControlList.Where（O =＆GT; o.pracid == c.pracid和放大器;＆安培; o.sex == c.sex和放大器;＆安培;
CaseSelectionList.AgeIsInRange（c.yob，o.yob，m_years）），
（C，O）=＆GT;
新{O，C}）取（m_ctrlno）。
 

解决方案

在你的code您定义2列表 CurrentCaseList，CurrentControlList ，但没有定义 CaseSelectionList 。

要获得3控制匹配一个情况下，对于这种见下文code：

在的SelectMany 方法来选择所有的订单，其中 TotalDue 小于500.00。

下面是code：

 十进制totalDue = 500.00M;
使用（AdventureWorksEntities上下文=新AdventureWorksEntities（））
{
    对象集＆LT;联系与GT;联系人= context.Contacts;
    对象集＆LT; SalesOrderHeader的＆GT;订单= context.SalesOrderHeaders;

    VAR的查询=
    contacts.SelectMany（
        触点=＆GT; orders.Where（为了=＆GT;
            （contact.ContactID == order.Contact.ContactID）
                ＆功放;＆安培; order.TotalDue＆LT; totalDue）
            。选择（为了=＆gt;新建
            {
                的ContactID = contact.ContactID，
                姓氏= contact.LastName，
                名字= contact.FirstName，
                订单ID = order.SalesOrderID，
                总= order.TotalDue
            }））;

    的foreach（查询VAR smallOrder）
    {
        Console.WriteLine（联系人ID：{0}名称：{1}，{2}订单ID：{3}总计由于：$ {4}，
            smallOrder.ContactID，smallOrder.LastName，smallOrder.FirstName，
            smallOrder.OrderID，smallOrder.Total）;
    }
}
 

I am matching Cases to Controls, basically records in the Case list, need to have the number of matches that is specified in the string m_ctrlno.

So far I have two lists, the where clause is correct, however I'm unsure how to use SelectMany to get the 3 Controls that match 1 Case. I decided to use the .Take() function however it doesn't seem to be working. I'm not getting the same case with 3 different controls when i cycle on the var query.

Here is the code:

List<CaseSelection> CurrentCaseList = new List<CaseSelection>();
foreach (CaseSelection CurrentCase in m_casesarraylist)
CurrentCaseList.Add(CurrentCase);

List<ControlSelection> CurrentControlList = new List<ControlSelection>();
foreach (ControlSelection CurrentControlRec in ControlList)
CurrentControlList.Add(CurrentControlRec);


var query = CurrentCaseList.SelectMany(
c => CurrentControlList.Where(o => o.pracid == c.pracid && o.sex == c.sex &&
CaseSelectionList.AgeIsInRange(c.yob, o.yob, m_years)),
(c, o) =>
new { o, c }).Take(m_ctrlno);

解决方案

In your code You define 2 list CurrentCaseList,CurrentControlList but not define CaseSelectionList.

To get the 3 controls that matches one case, for this see below code:

the SelectMany method to select all orders where TotalDue is less than 500.00.

Here is the code:

decimal totalDue = 500.00M;
using (AdventureWorksEntities context = new AdventureWorksEntities())
{
    ObjectSet<Contact> contacts = context.Contacts;
    ObjectSet<SalesOrderHeader> orders = context.SalesOrderHeaders;

    var query =
    contacts.SelectMany(
        contact => orders.Where(order =>
            (contact.ContactID == order.Contact.ContactID)
                && order.TotalDue < totalDue)
            .Select(order => new
            {
                ContactID = contact.ContactID,
                LastName = contact.LastName,
                FirstName = contact.FirstName,
                OrderID = order.SalesOrderID,
                Total = order.TotalDue
            }));

    foreach (var smallOrder in query)
    {
        Console.WriteLine("Contact ID: {0} Name: {1}, {2} Order ID: {3} Total Due: ${4} ",
            smallOrder.ContactID, smallOrder.LastName, smallOrder.FirstName,
            smallOrder.OrderID, smallOrder.Total);
    }
}

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