[SalesForce] Calling Batch class dynamically using custom Interface

I had a business case to run Batch class concurrently, I was successfully able to accomplish that by writing another Batch class which creates chunks of data and call main Batch class n number of times. Now I am trying to make that concurrent class generic so that it can work with any sObject and be able to call any Batch class whose name I will be passing through custom setting.

I am using Type class to implement this.

I have used this in past and it works fine with Apex classes but in case of Batch class I am getting below error:

Compile Error: Argument must be an object that implements Database.Batchable at line 87 column 17

Type classType = Type.forName('MyBatchClassName');
MyInterFaceName obj = (MyInterFaceName)classType.newInstance();
obj.runBatchConcurrently(); // This is the method which I declared in Interface and implemented in Batch class               
system.debug('### obj'+obj); // In debug I am able to see instance of my Batch class
database.executeBatch(obj, 200); // Compile error is coming here

Best Answer

You must cast your instance to a Database.Batchable if you want to pass it to a Database.executeBatch call, even if you additionally implement a custom interface.

Type classType = Type.forName('MyBatchClassName');
MyInterfaceName instance = (MyInterfaceName)classType.newInstance();
// custom interface methods

Database.executeBatch((Database.Batchable<sObject>)instance, 100);

Related Solutions

[SalesForce] Argument must be an object that implements Database.Batchable

Your class has to implement the interface, so that the platform can cast it to Database.Batchable and pass it to the Database.executeBatch method (which requires a parameter of this type).

global class CBatchCalculateRatingsHistoricalData implements Database.Batchable<sObject>

Note: Also you no longer need to make the class and its methods global, unless you want to expose the class to code outside your package.

This is a really useful topic in the developers guide, it also covers best practices on testing Batch Apex.

[SalesForce] simple way to serialize execution of Batchable class

I think using Batch Apex chaining is closer to what your aiming for here, though not as bullet proof as a scheduled job reviewing records that have yet to have a Geocode calculated. As while this is not as immediate, it does, as you've said give more predictable processing (may need to still consider schedule overlaps though) and has some built in error handling and retry semantics to it.

That said some notes on the chaining approach...

Ensuring there can be only one! You could query the AsyncApexJob by class Id to determine if a job is already running before starting another. Though there is still a small concurrency issue, as you cannot guarantee at that precise moment another parallel trigger invocation does not make the same query and arrive at the same answer (since there is no lock on the AsyncApexJob records). This could be quite a high likelihood if your hammering in a lot of Accounts. What you could do if you are concerned about this is use a custom object as a semaphore, this object has a unique constraint field on it, preventing multiple inserts if duplicates records are found. If you fail to insert into it, prior to attempting to star the job, you can take this as a sign the job is still running. When your job is completely done (see below) this record is removed.
Chainging the jobs. As you mentioned in the finish method you can start a new batch job if you determine new unprocessed Accounts have been inserted in the meantime. Be sure not to delete the semaphore record though, until you know you've not got any more work to do. As other trigger invocations maybe attempt to start a new job inbetween the transition between the current job ending and the new one starting. There is one other consideration here as well, only a maximum of 5 batch jobs can be queued/running in the org, so the chain could get broken. One solution to this is to query as per this answer and schedule a job in the future (using the new batch schedule feature) to try again, see this answer for more detail Cascading batch jobs.

Risk Management. As you can see there is some risk in the above, its a mater of judging the likelihood vs the overhead of the users in resolving the effects of the processing not occurring. For example you could have a button on the Account page as fall back to calculate as and when needed. Or have a scheduled job act as a secondary sweeper kicking off your job every day to check for records that have not been processed (again using the semaphore). Thus giving the users a near realtime update, with the added security in knowing the sweeper will pick up instances where the chaining fails due to fringe cases such as batch apex job governor and/or remaining concurrency issues in the solution.

When all is said and done... At the end of the day, triggers and batch jobs (or @future for that matter) don't mix that well. The advice in the Apex docs to think carefully about using them is a little to tame when you really start to think about all the considerations of starting jobs from a trigger context. That said, if you known and accept the potential points of failure and have some plan to observe and address them if they occur it can be acceptable.

Use extreme care if you are planning to invoke a batch job from a trigger. You must be able to guarantee that the trigger will not add more batch jobs than the five that are allowed. In particular, consider API bulk updates, import wizards, mass record changes through the user interface, and all cases where more than one record can be updated at a time.

Hope this helps!

Best Answer

Related Solutions

[SalesForce] Argument must be an object that implements Database.Batchable

[SalesForce] simple way to serialize execution of Batchable class

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