External Datasource are the source of truth for the external objects in Salesforce.
For Example, you are having customer data in an MySQL server out of your Salesforce Environment then MySQL is the External Data source and the tables inside external data source are known as External Objects
- External objects are similar to custom objects, except that they map to data that’s stored outside your Salesforce org.
- Each external object relies on an external data source definition to connect with the external system’s data
- Each org can have up to 200 external objects. External objects don’t count toward the amount for custom objects.
SOQL Considerations for Salesforce Connect
- Each SOQL query can have up to 4 joins across external objects and other types of objects.
- External objects don’t support the following aggregate functions and clauses.
- AVG() function
- COUNT(fieldName) function (however, COUNT() is supported)
- HAVING clause
- GROUP BY clause
- MAX() function
- MIN() function
- SUM() function
Page Layout Limit for External Object
- You can’t rename a page layout if you’re using Salesforce Professional Edition.
- In Lightning Experience, page layouts support up to 55 lookup fields. In Salesforce Classic, page layouts support up to 40 lookup fields.
1 – Link to External DataSource – https://orderdb.herokuapp.com/orders.svc
2 – https://trailhead.salesforce.com/content/learn/projects/quickstart-lightning-connect
3 – https://help.salesforce.com/articleView?id=platform_connect_considerations.htm&type=0
4 – https://developer.salesforce.com/docs/atlas.en-us.object_reference.meta/object_reference/sforce_api_objects_external_objects.htm