How does joining two custom objects into one custom object through master-detail relationship work

Question

I've been working on a test method but I've had a problem creating the setup of it.

public static List<Job_Posting__c> createPostings(){
        List<Job_Posting__c> testPostings = new List<Job_Posting__c>();
        List<Position__c> testPositions = new List<Position__c>();
        List<Employment_Website__c> testEmploymentWebsites = new List<Employment_Website__c>();

        for(Integer i=0; i<10; i){
            testPositions.add(new Position__c(Name = 'Test '+ i, Status__c = 'Closed - Filled'));
            insert testPositions;
            testEmploymentWebsites.add(new Employment_Website__c(Name = 'Test' +i));
            insert testEmploymentWebsites;
            testPostings.add(testPostions, testEmploymentWebsites);

        }
        return testPostings;

I know my insertion of into testPostings is wrong but how would I insert both into it. I know both Position and EmploymentWebsites will share a name. So would I insert that way?

Answer 1

You would create the parents first, then children later. This means using multiple for loops and moving the DML operations out of the loop. Here's a basic modification with some assumptions thrown in.

List<Job_Posting__c> testPostings = new List<Job_Posting__c>();
List<Position__c> testPositions = new List<Position__c>();
List<Employment_Website__c> testEmploymentWebsites = new List<Employment_Website__c>();

for(Integer i=0; i<10; i){
    testPositions.add(new Position__c(Name = 'Test '+ i, Status__c = 'Closed - Filled'));
    testEmploymentWebsites.add(new Employment_Website__c(Name = 'Test' +i));
}
insert testPositions;
insert testEmploymentWebsites;
for(Integer i=0; i<10; i){
    testPostings.add(new Job_Posting__c(Position__c=testPositions[i].Id, Employment_Website__c=testEmploymentWebsites[i].Id));
}
insert testPostings;
return testPostings;

This code assumes that Job Posting is a many-to-many relationship object, and the field names match the object names. You may need to adjust the field names accordingly.