Lightning Connect is a Salesforce feature that allows integrations with external systems. Before Winter 16 release, it only read-only capabilities were provided. Since Winter 16, writable datasources were delivered, making Lightning Connect a very interesting option to think about.
In order to work with Lightning Connect you have to declare an External Datasource, and a way to access this external datasource. This is, if your datasource understands the OData protocol, Salesforce provides OData adapters. In addition, Salesforce gives us the capability of writing a custom adapter in Apex for reading any kind of datasources. You can take a look at this interesting post about how to create a custom adapter.
Playing with External Datasources, I found an interesting option that you can use, which is declaring it as a “High Data Volume External Datasource“. This option is available with OData adapters as well as with custom adapters:
What does this option mean? Well, as everything in Salesforce, accessing external objects through external datasources has limits. The general external data integration limits can be seen here.
However, if your external datasource is hitting rate limits, you have the option of transforming it into a High-Volume one.
The documentation says that doing so bypasses most of the rate limits. However, external objects that are associated with high-data-volume external data sources aren’t available in Salesforce1 and don’t support record feeds.
In addition, doing some tests with High-Volume datasources I have found some interesting facts:
Using a Non High-Volume Datasource, I noticed that Salesforce assigns an Id over the scenes to each one of the external objects you access in the system (I guess it stores an equivalence between the real ExternalIds of the objects and the “virtual” Ids it had assigned to them somehow).
This is, each time a new external object is retrieved, Salesforce will assign an Id for each external object, as we can see in the following listview:
Knowing a record’s Id, then, we can then perform SOQL queries based on that Id, even if we don’t know its ExternalId:
[SELECT Id FROM Restaurant__x WHERE Id = 'x0058000000CaiD']
Salesforce will automatically translate this query to a query which filters by the related ExternalId, which is the query that will arrive in the end to your custom adapter implementation (if you are using a custom one, which is my case):
[SELECT Id FROM Restaurant__x WHERE ExternalId = 'ChIJvZ8va577cQ0RsMv3_vNLzz0']
However, if the datasource is a High-Volume one, no Ids are set and the Id field is not available for being added to the list view! So the only possible queries we could do will be ExternalId based queries.
This fact has implications when developing a pair of Visualforce pages for having a customized list – detail navigation.
In the first case (Non High-Volume datasource), we are able to add Id-based detail navigation links to the list page, and query the detail page information through the object Id, as Salesforce is able to translate this “virtual ” Id to an ExternalId field. For example having this link:
In the controller of your detail page you can query your object’s information using the Id:
However, in the second case (High-Volume datasource), if we have the same implementation, all links will point to Id “
000000000000000AAA“, which is an standard empty key Id from Salesforce.
Then, in that case, one option is to create your detail links based on ExternalIds, and parse the ExternalId parameter in your detail page controller for querying your detail page information through the received ExternalId.
Indeed, if we retrieve the metadata that defines an External Datasource, we find that setting a datasource as a High-Volume one at metadata level is done adding the next property:
To finish I just want to add that according to the documentation, High-data-volume external data sources are still limited to 10,000 OData queries per hour for Enterprise, Performance, and Unlimited Editions for OData adapters, but higher limits are available on request.