Test.loadData() - undocumented (but useful) behavior loading relationships

Moving question into answer

And the answer appears to be yes (a tip to a colleague of mine who discovered this) and it works for master-detail relationships too

The Proof

• Account
• Contact with lookup relationship AccountId and custom lookup Alternate_Account__c

Here's the CSV file for the Account - note the values of 0 and 1 for the test Account.ID rows:

And here's the CSV for the Contacts - note the values in the AccountId column and Alternate_Account__c column reference the artificial IDs of Account CSV rows:

Using this Apex testmethod, I loaded the Accounts data from the static resource first and then the Contacts data from its static resource. I displayed the constructed SObject relationships using System.debug:

@isTest
private class TestStaticResourceDataLoad {
    private static void testStaticResourceDataLoadMasterDetail() {
        List<SObject> aList = Test.loadData(Account.sObjectType,'testAccounts');
        List<SObject> cList = Test.loadData(Contact.sObjectType,'testContacts');

        String res = '';
        for (Account a: [select id, name, (select id, firstname, lastName,email, 
                                 reportsTo.lastname, alternate_account__r.name from Contacts) 
                             from Account where id IN :aList]) {
            String cRes = '';
            for (Contact c: a.contacts)
                cRes += '\n...name= ' + c.firstName + ' ' + c.lastName + ' ' + c.email + 
                             ' altAcct=' + c.alternate_account__r.name;
            res += '\n account id/name: ' + a.id + ' ' + a.name + ' w/ contacts: ' + cRes;
        }
        System.debug(LoggingLevel.INFO,'res='+res);
    }
}

And here are the results:

13:11:43.657 (3657616477)|USER_DEBUG|[15]|INFO|res=
 account id/name: 001m0000007pN6hAAE 00AccountName w/ contacts: 
   name= 0.0fname 0.0lname [email protected] altAcct=01AccountName
   name= 0.1fname 0.1lname [email protected] altAcct=01AccountName
 account id/name: 001m0000007pN6iAAE 01AccountName w/ contacts: 
   name= 1.0fname 1.0lname [email protected] altAcct=00AccountName

The Contacts are appropriately parented and the Contact.alternate_account__c lookup is also accurate.

Side note - what does not work is references within a StaticResource dataset. For example, I tried to use the Contact.ReportsToId field to have one Contact be a child of another in the same batch as shown here:

This isn't surprising as the Sobjects are inserted as a batch and the intra-Sobject reference is not resolvable yet. No different than using DataLoader.

Side note 2 Another use case I couldn't get to work via this approach was loading PricebookEntry rows for the standard pricebook unless you used the actual ID of the standard Pricebook as you can't insert a standard pricebook via testmethods. This can have some portability issues

Summary

What is striking to me is that across Apex statement executions (the successive Test.loadData(..) lines), SFDC keeps track of a mapping between real IDs of the loaded Sobject and the fake ID you specify in the CSV file so you can build relationships. None of this is documented in the Apex Developer's Guide and the casual developer could easily assume that Test.loadData(..) can only load top level SObjects or otherwise force the developer to post-process and add the relationships later.

For the Side Note: Its is valid. There is no way to populate self lookups. But that can be feasible if SFDC can start supporting batch number as parameter to this method Test.loadData ( even in that case first record will be left out )

It is a good observation to see that ID field can be manipulated and relationship between the parent and child can be maintained. I think Salesforce should update this behavior as it is a key feature to use the full capability of Test.loadData method. Missing in documentation has resuilted in this post for Fake Fields https://help.salesforce.com/apex/HTViewSolution?id=000167032&language=en_US Actually if documentation is added for this then workaround of the above post is not needed.

You can check this and see if it deserves to vote this idea https://success.salesforce.com/ideaView?id=08730000000kxHhAAI

Thanks Amit