== Why is this an issue?

In order to protect shared resources, Salesforce enforces a maximum number of DML statements which can be executed inside a single https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_transaction.htm[transaction]. This is part of https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/apex_gov_limits.htm[Governor limits]. If a DML statement is nested inside a loop's body (For/While/Do-While) it might be executed more times than the Governor limit allows, making the code fail.


Thus it is a best practice to not have DML statements nested in the body of loops and instead perform the DML operation on a list of sObjects.


This rule raises an issue when it detects DML statements inside a loop.


=== Noncompliant code example

[source,apex]
----
public class myDMLLoop {
    public static void myFunction() {
        for (Task task: [Select Id, subject from Task]) {
            if (task.subject == 'foo') {
                task.subject = 'bar';
                update task; // Noncompliant
            }
        }
    }
}
// Query in a while loop
public class myDMLLoop {
    public static void myFunction(Task[] tasks) {
        Integer i = 0;
        while ( i < 1000) {
            Task task = tasks[i];
            if (task.subject == 'foo') {
                task.subject = 'bar';
                update task; // Noncompliant
            }
        }
    }
}

// Query in a do-while loop
public class myDMLLoop {
    public static void myFunction(Task[] tasks) {  
        Integer i = 0;
        do {
            Task task = tasks[i];
            if (task.subject == 'foo') {
                task.subject = 'bar';
                update task; // Noncompliant
            }
            i++;
        } while (i < 1000);
    }
}
----


=== Compliant solution

[source,apex]
----
public class myDMLLoop {
  	public static void myFunction() {
		List<Task> updatedTasks = new List<Task>();
        for (Task task: [Select Id, subject from Task]) {
            if (task.subject == 'foo') {
                task.subject = 'bar';
                updatedTasks.add(task);
            }
        }
        update updatedTasks;
    }
}
----


== Resources

* https://developer.salesforce.com/index.php?title=Apex_Code_Best_Practices&oldid=26951[Apex Code Best Practices]
* https://developer.salesforce.com/docs/atlas.en-us.apexcode.meta/apexcode/langCon_apex_loops_for_SOQL.htm[SOQL For Loops]


ifdef::env-github,rspecator-view[]

'''
== Implementation Specification
(visible only on this page)

=== Message

Move this DML statement out of the loop or process sObjects by batch.


'''
== Comments And Links
(visible only on this page)

=== on 5 Jul 2019, 17:35:38 Nicolas Harraudeau wrote:
If the rule raise false positives one possible exception is:


=== Exceptions

No issue will be raised when the DML statement is executed on a collection returned by a for loop. In this case the for loop already executed the DML statement in bulk.


----
public class myDMLLoop {
    public static void myFunction() {
        for (Task[] task: [Select Id, subject from Task]) { // Ok. The SOQL query is processing a batch of Tasks instead of a single one
        	task.subject = task.subject + ' processed';
        	update task; // This update a batch of Tasks
        }
        for (List<Task> tasks: [Select Id, subject from Task]) { // Same here
            for (Task task: tasks) {
        		task.subject = task.subject + ' processed';
            }
            update tasks;
         }
    }
}
----

endif::env-github,rspecator-view[]