How to sort list items for Date field value (Apex, Salesforce)

Question

With Salesforce's Apex, is there any way to sort list items, for Date field value. Please refer the TODO section of the following code, thanks.

/**
 * Select list of jobOccurrences belongs to particular list of jobs
 */
private List<Job_Occurrence__c> getJobsByJobCode(List<Job__c> jobList) {

 // Select relevant Job Occurrence objects 
    List<Job_Occurrence__c> jobOccuList = new List<Job_Occurrence__c>();

    for (Job__c job : jobList) {  

         Job_Occurrence__c jobOccurrence = [SELECT Id, Job__c,  
                                                   Schedule_Start_Date__c 
                                            FROM Job_Occurrence__c 
                                            WHERE Job__c =: job.Id];

         if((jobOccurrence != null) && (jobOccurrence.Id != null)) {
            jobOccuList.add(jobOccurrence);
         }        
    }   

    if((jobOccuList != null) && (jobOccuList.size() > 0)) {

       // TODO
       // How I sort the 'jobOccuList' with Date field 'Schedule_Start_Date__c',   
       // for select the items according to sequence of latest jobOccurrence    

       return jobOccuList; 

    } else {
       throw new RecordNotFoundException ('Could not found any jobOccurrence for given list of jobs');   
    }                            
}

Answer 1

You really should bulkify this code, i.e. not run a query inside a loop which could cause potentially cause issues with the governor limits, and since you just want the combined list for all Job__c records this makes your ordering easy too — you can do it in the query!

The code you want to change is this:

// Select relevant Job Occurrence objects 
List<Job_Occurrence__c> jobOccuList = new List<Job_Occurrence__c>();

for (Job__c job : jobList) {  

     Job_Occurrence__c jobOccurrence = [SELECT Id, Job__c,  
                                               Schedule_Start_Date__c 
                                        FROM Job_Occurrence__c 
                                        WHERE Job__c =: job.Id];

     if((jobOccurrence != null) && (jobOccurrence.Id != null)) {
        jobOccuList.add(jobOccurrence);
     }        
}

Essentially we can optimise this to not only use one query instead of N (where N is jobList.size()) and get them ordered at the same time. First we need to gather the list of Job__c IDs, and then we can use the IN statement in the WHERE clause of the SOQL:

// Select relevant Job Occurrence objects 
List<Job_Occurrence__c> jobOccuList;
Set<Id> setJobIds = new Set<Id>();

setJobIds.addAll(jobList);

// get the job occurances starting with the latest, use ASC for reverse!
jobOccuList = [SELECT Id, Job__c, Schedule_Start_Date__c 
               FROM   Job_Occurrence__c 
               WHERE  Job__c IN : setJobIds
               ORDER BY Schedule_Start_Date__c DESC];

Finally, if you need to be able to easily map back from the Job_Occurrence_c records to Job_c records, you could replace the set with a map as below, though given that you just want this list I don't think it's needed here (just providing it for completeness).

Map<Id, Job__c> mapJobs = new Map<Id, Job__c>();

for (Job__c job : jobList) {
    mapJobs.put(job.Id, job);
}

** snip **

for (Job_Occurrence__c jobOccu : jobOccuList) {
    Job__c theJob = mapJobs.get(jobOccu.Job__c);
    // do stuff with the job
}

All of this code has been written in browser, so there may be some syntax errors but it should be good!