如何按每个 id 映射列表中的最新记录？

如何解决如何按每个 id 映射列表中的最新记录？

我在 apex 类中有一个方法，可以从案例的电子邮件中获取附件 (ContentDocument)，并将其添加到另一个案例中。为了完成我的代码，下面有两个问题：

1. 如何创建逻辑来获取电子邮件列表，其中每个案例我只需要最新的电子邮件？

2. 如何创建逻辑以获取在此方法中传递的 srID 列表？

以下代码的适当部分提到了这两个问题：

public static void AttFromParenttoClonedCaseList(list<ID>srID){

    list< ContentDocumentLink>  attchlist2=new list< ContentDocumentLink>(); 
    Map<Id,Case> mapCasess = new Map<Id,Case>(); 
    Map<Id,EmailMessage> mapEmail = new map<Id,EmailMessage>();
    Map<Id,EmailMessage> mapemailmessageId = new Map<Id,EmailMessage>();
    List<String> externalIdCases = new List<String>();  
    List<String> casesID = new List<String>(); 
    List<Case> ListCaseNumber = new List<Case>([SELECT ID,External_ID__c From Case WHERE ID IN :srID]);
    
    for (Case mpC : ListCaseNumber){
        mapCasess.put(mpC.id,mpC);
    } 
    
    for (Case Listcase : ListCaseNumber) {  
        externalIdCases.add(Listcase.External_ID__c);
    }     
    List<Case> ListCaseID = new List<Case>([SELECT ID From Case WHERE ID IN :externalIdCases]);    
    
    for (Case listIdcases : ListCaseID) {  
        casesId.add(listIdcases.id);
    }    
    
    Map<id,EmailMessage> listEmailMessage = new Map<id,EmailMessage>([SELECT parentID,ID From EmailMessage WHERE parentID IN :casesId order by parentid,createddate desc]);
    
    \\How to create logic to get list of e-mails where I need only the newest e-mail for each case (base on list listEmailMessage above)?   
    
    List<ContentDocumentLink> contentdocumentId = new List<ContentDocumentLink>([SELECT ID,ContentDocumentId FROM ContentDocumentLink WHERE LinkedEntityId IN :/*list of emailmessages*/]);
    
    for (ContentDocumentLink links : contentdocumentId){
                       
              ContentDocumentLink linkAtt = new ContentDocumentLink(); 
                             
              linkAtt.LinkedEntityId = \\how can I create logic to get list of srID passed in this method?
              linkAtt.ContentDocumentId = links.ContentDocumentId;       
              linkAtt.ShareType = 'V';         
              linkAtt.Visibility = 'AllUsers';
              attchlist2.add(linkAtt);                                            
    }             
    if (attchlist2.size() > 0)                
    insert attchlist2;          
}

解决方法

如何创建逻辑来获取我只需要的电子邮件列表 每个案例的最新电子邮件？

这样的事情应该是一个好的开始

SELECT Id,CaseNumber,Subject,(SELECT Id,FromAddress,ContentDocumentIds
    FROM EmailMessages 
    WHERE Incoming = true 
    ORDER BY CreatedDate DESC 
    LIMIT 1)
FROM Case
LIMIT 10

将其视为“父级 + 相关列表、过滤、排序”比“给我此父级的所有电子邮件，我将使用它们构建地图或其他东西，手动循环遍历它们，比较日期以选择最多”更简单最近的...”。我有一段时间没有使用电子邮件，因此您可能需要更多过滤器，但这是一个好的开始。

如何创建逻辑以获取在此方法中传递的 srID 列表？

不确定我是否理解。您想将旧案例电子邮件中的附件重新链接到新案例吗？看看 ContentDocumentIds 是否足以建立新链接。如果不是 - 遍历我的查询结果，收集所有 EmailMessage Id 并查询 ContentDocumentLinks WHERE LinkedEntityId IN :emailMessageIds?

检查这是否编译？

// I don't really need it as a Map,list seems to be fine. But looks like you wanted Maps so I went with map.
// Map might be useful if External_ID__c is not a lookup.
// If you want a list (or set) of Ids from a query the very easy trick is to do
// Set<Id> myIds = new Map<Id,Account>([SELECT Id FROM Account LIMIT 5]).keyset();
// Anyway.

// "External_ID__c" is a lookup to Case or something else? Assuming it's just a lookup,bit like "ParentId".
Map<Id,Case> originals = new Map<Id,Case>([SELECT Id,External_ID__c,External_ID__r.CaseNumber,ContentDocumentIds
        FROM EmailMessages 
        WHERE Incoming = true 
        ORDER BY CreatedDate DESC 
        LIMIT 1)
    FROM Case
    WHERE Id IN :srId AND External_ID__c != null]);

List<ContentDocumentLink> links = new List<ContentDocumentLink>();
for(Case original : originals.values()){
    System.debug('source: ' + original);
    System.debug('target: ' + original.External_ID__r.CaseNumber);
    
    if(!original.EmailMessages.isEmpty()){
        List<String> documentIds = original.EmailMessages[0].ContentDocumentIds;
        for(String i : documentIds){
            links.add(new ContentDocumentLink(
                LinkedEntityId = original.External_ID__c,ContentDocumentId = i,ShareType = 'V',Visibility = 'AllUsers'
            ));
        }
    }
}
insert links;