[SalesForce] query locator with string query or sobject list

Using the Database.QueryLocator object bypasses the governor limit for the total number of records retrieved by SOQL queries. One could implement one of the following methods to get the QueryLocator:

global static Database.QueryLocator getQueryLocator(List<SObject> query){}

global static Database.QueryLocator getQueryLocator(String query){}

I see many examples in the salesforce site using Database.QueryLocator getQueryLocator(String query) instead of Database.QueryLocator getQueryLocator(List<SObject> query).

Why using Database.QueryLocator getQueryLocator(String query)? It is easier to make mistakes using a query string. Does Database.QueryLocator getQueryLocator(List<SObject> query) also retrieve at most 50 million records?

Best Answer

Database.QueryLocator getQueryLocator(List<SObject> query) only works with an inline query.

The following would compile:

public class SuperBatch implements Database.Batchable<SObject>, Database.Stateful {
    public Database.QueryLocator start(Database.BatchableContext param1) {
        return Database.getQueryLocator([SELECT Id FROM Account]);
    }

    public void execute(Database.BatchableContext param1, List<Account> accountsList) {
    }

    public void finish(Database.BatchableContext param1) {
    }
}

The following would NOT compile:

public class SuperBatch implements Database.Batchable<SObject>, Database.Stateful {
    public Database.QueryLocator start(Database.BatchableContext param1) {
        return Database.getQueryLocator(getAccounts());
    }

    public void execute(Database.BatchableContext param1, List<Account> accountsList) {
    }

    public void finish(Database.BatchableContext param1) {
    }

    private List<Account> getAccounts(){
        return [SELECT Id FROM Account];
    }
}

The last example would not compile and salesforce would show the error message:

Argument must be an inline query

Why using Database.QueryLocator getQueryLocator(String query)?

  • Using Database.QueryLocator getQueryLocator(String query) allows code reusability, since once could write a query string in a method and use it elsewhere.

Does Database.QueryLocator getQueryLocator(List<SObject> query) also retrieve at most 50 million records?

  • Yes, it does.
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