How To Write A Batch Class For Scheduled Deletion?

Question

I have a custom object and I have created a lot of records in past days, now I want to delete the records which have been created before 7 days. How can I do it?

Answer 1

You can just run an anonymous script if "a lot of records" is less than 10k.

delete [SELECT Id FROM MyObject__c WHERE CreatedDate < LAST_N_DAYS:7];

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If you have more records than that, I recommend plugging the above SOQL into Data Loader. Export all matching records, then upload the resulting CSV in a delete job.

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If you're dead set on writing a batch, you can create a QueryLocator with that query.

public Database.QueryLocator start(Database.BatchableContext context)
{
    return Database.getQueryLocator([/*above query*/]);
}

And your execute method should be pretty straightforward...

public void execute(Database.BatchableContext context, List<SObject> records)
{
    delete records;
}

Answer 2

Not sure if this applies, but if it should be scheduled in the sense of: Everyday, delete all records that are more than 7 days old, you can write the batch with the start and execute methods specified by Adrian Larson. In addition, have the batch class implement Schedulable and add a second execute method, like so

global class OldDataDeleter implements Database.Batchable<sObject>,Schedulable{
    static Date today7 = Date.today().addDays(-7);

    public Database.QueryLocator start(Database.BatchableContext context)
    {
        return Database.getQueryLocator('Select ID from Custom_Object__c where CreatedDate < :today7');
    }

    public void execute(Database.BatchableContext context, List<SObject> records)
    {
        delete records;
    }

    global void execute(SchedulableContext ctx) 
    {
        Database.executeBatch(new OldDataDeleter());
    }
}

You can then schedule this batch to run daily within Salesforce setup - there's a button in the Apex Classes section to do so.