Simultaneous INSERTs with Heroku Connect in the same transaction

So had some fun working with Heroku Connect the other day writing some data from Heroku to Salesforce using Postgres. On Heroku that is easily done using Heroku Connect which is a turn-key solution we have for that. Easy to use and easy to setup. The way it works is that you configure a connection from Heroku to Salesforce, map it to a Postgres database on Heroku and selects the objects and fields from Salesforce to synchronize and Heroku Connect does the rest. Powerful stuff!

So what did I do and what did I learn…

In Salesforce I have two custom objects – a parent custom object (Parent__c) and a child custom object (Child__c) with a master-detail relation to the parent (Parent__r / Parent__c). Both the Parent and Child custom objects have an external ID (External_ID__c) to make writing back from Heroku easy.

Once the objects are mapped using Heroku Connect I get 2 new tables in the “salesforce”-schema in Postgres (“salesforce.parent__c” and “salesforce.child__c”) with the selected fields.

What I wanted to do was – in a transaction – write a new parent record and the associated child records. I’m using node.js but since I’m using raw SQL that shouldn’t be too different to any other language. What I did do however is use promises which is important for this post.

Below is some code to illustrate what I did. Basically the code does the following:

1. Starts a transaction (BEGIN)
2. Inserts the parent record (INSERT INTO salesforce.parent__c…)
3. Creates a promise to insert the 3 child records (INSERT INTO salesforce.child__c…) and resolves them all at once (i.e. the inserts will happen simultaneously)
4. Commits the transaction (COMMIT) if all is good or rolls it back (ROLLBACK)

// data to work with
const objData = {
   "id": "ffe16a92-0f22-4a16-947a-461d307b4905", 
   "text": "Some Parent Text...", 
   "children": [
      {"id": "ffe16a92-0f22-4a16-947a-461d307b5906", "text": "Child1"},
      {"id": "ffe16a92-0f22-4a16-947a-461d307c4907", "text": "Child2"},
      {"id": "ffe16a92-0f22-4a16-947a-461d307b3904", "text": "Child3"}
   ]
};

// start a new tx
pool.query("BEGIN").then(rs => {
   // insert parent record
   return pool.query(`INSERT INTO salesforce.parent__c 
      (External_ID__c, Text__c) 
      VALUES 
      ('${objData.id}', '${objData.text}');`);
}).then(rs => {
   // map each child to a promise to insert child record
   const promises = objData.children.map(child => {
      return pool.query(`INSERT INTO salesforce.Child__c 
         (parent__r__external_id__c, "External_ID__c", "Text__c") 
         VALUES 
         ('${objData.id}', '${child.id}', '${child.text}')`);
   return Promise.all(promises);
}).then(rs => {
   // commit tx
   console.log("Commiting tx");
   return pool.query("COMMIT");
}).catch(err => {
   // roll tx back
   console.log(`Rolling back tx: ${err.message}`);
   return pool.query("ROLLBACK");
})

The issue was that I kept seeing 2 errors in the log when the code ran as shown below. Funny thing is that I didn’t see any information about the transaction being rolled back.

2019-03-16T14:32:20-07:00 event="record 8 ERROR ↑SALESFORCE [SOAP] Foreign key external ID: ffe16a92-0f22-4a16-947a-461d307b4905 not found for field External_ID__c in entity Parent__c" addon_id=ba3d4995-092d-4095-aa5e-7ac41981bd93 object_type=sync object_id=ba3d4995-092d-4095-aa5e-7ac41981bd93 state=POLLING_DB_CHANGES level=debug  
22019-03-16T14:32:20-07:00 event="record 9 ERROR ↑SALESFORCE [SOAP] Foreign key external ID: ffe16a92-0f22-4a16-947a-461d307b4905 not found for field External_ID__c in entity Parent__c" addon_id=ba3d4995-092d-4095-aa5e-7ac41981bd93 object_type=sync object_id=ba3d4995-092d-4095-aa5e-7ac41981bd93 state=POLLING_DB_CHANGES level=debug  

Okay so clearly the insert fails because the foreign key of the child records cannot be resolved i.e. the ID pointing from salesforce.child__c to salesforce.parent__c. But why only 2 errors and not 3 errors? (I was attempting to insert 3 child records) I added an intermediate COMMIT before inserting the child records and started a new transaction and then all was well. So it had to do with the transaction… In Postgres the solution would be to defer the referential constraint check but I couldn’t do it. Why? Because Heroku Connect doesn’t use constraints as can be seen if inspecting the child table (psql: “\d salesforce.child__c”) but seems to do the referential integrity check using a trigger on the tables created by Heroku Connect. I’m guessing this is part of the magic that it Heroku Connect.

I played a bit more around with the code and finally solved the issue by doing the inserts in turn by resolving the promises sequentially. So instead of using Promise.all (that resolves the promises simultaneously) I resolved each promise in turn and then it worked.

My understanding of this is must be as follows. The triggers created by Heroku Connect that handles the underlying integration to Salesforce uses some log-tables (as described in the documentation) but the triggers must also employ some locking of the salesforce.parent__c table and hence the other inserts to salesforce.child__c running at the same time fails. Also this doesn’t cause my transaction to roll back which from my point of view is unfortunate as I really want the inserts to be atomic hence the use of a transaction. In this case there was a solution in doing the inserts sequentially. I’ll follow up internally in Salesforce and see if I can provide a better answer that the above.