How to get Salesforce REST API to paginate? - python-3.x

Question

I'm using the simple_salesforce python wrapper for the Salesforce REST API. We have hundreds of thousands of records, and I'd like to split up the pull of the salesforce data so all records are not pulled at the same time.
I've tried passing a query like:
results = salesforce_connection.query_all("SELECT my_field FROM my_model limit 2000 offset 50000")
to see records 50K through 52K but receive an error that offset can only be used for the first 2000 records. How can I use pagination so I don't need to pull all records at once?

Answer 1

Your looking to use salesforce_connection.query(query=SOQL) and then .query_more(nextRecordsUrl, True)
Since .query() only returns 2000 records you need to use .query_more to get the next page of results
From the simple-salesforce docs
SOQL queries are done via:
sf.query("SELECT Id, Email FROM Contact WHERE LastName = 'Jones'")
If, due to an especially large result, Salesforce adds a nextRecordsUrl to your query result, such as "nextRecordsUrl" : "/services/data/v26.0/query/01gD0000002HU6KIAW-2000", you can pull the additional results with either the ID or the full URL (if using the full URL, you must pass ‘True’ as your second argument)
sf.query_more("01gD0000002HU6KIAW-2000")
sf.query_more("/services/data/v26.0/query/01gD0000002HU6KIAW-2000", True)
Here is an example of using this
data = [] # list to hold all the records
SOQL = "SELECT my_field FROM my_model"
results = sf.query(query=SOQL) # api call
## loop through the results and add the records
for rec in results['records']:
rec.pop('attributes', None) # remove extra data
data.append(rec) # add the record to the list
## check the 'done' attrubite in the response to see if there are more records
## While 'done' == False (more records to fetch) get the next page of records
while(results['done'] == False):
## attribute 'nextRecordsUrl' holds the url to the next page of records
results = sf.query_more(results['nextRecordsUrl', True])
## repeat the loop of adding the records
for rec in results['records']:
rec.pop('attributes', None)
data.append(rec)
Looping through the records and using the data
## loop through the records and get their attribute values
for rec in data:
# the attribute name will always be the same as the salesforce api name for that value
print(rec['my_field'])
Like the other answer says though, this can start to use up a lot of resources. But it what you're looking for if want to achieve page nation.
Maybe create a more focused SOQL statement to get only the records needed for your use case at that specific moment.

Answer 2

LIMIT and OFFSET aren't really meant to be used like that, what if somebody inserts or deletes a record on earlier position (not to mention you don't have ORDER BY in there). SF will open a proper cursor for you, use it.
https://pypi.org/project/simple-salesforce/ docs for "Queries" say that you can either call query and then query_more or you can go query_all. query_all will loop and keep calling query_more until you exhaust the cursor - but this can easily eat your RAM.
Alternatively look into the bulk query stuff, there's some magic in the API but I don't know if it fits your use case. It'd be asynchronous calls and might not be implemented in the library. It's called PK Chunking. I wouldn't bother unless you have millions of records.