DML Statements vs. Database Class Methods
Apex offers two ways to perform
DML operations: using DML statements or Database class methods. This provides
flexibility in how you perform data operations. DML statements are more
straightforward to use and result in exceptions that you can handle in your
code. This is an example of a DML statement to insert a new record.
// Create the list of sObjects to insert
List<Account> acctList = new
List<Account>();
acctList.add(new Account(Name='Acme1'));
acctList.add(new Account(Name='Acme2'));
// DML statement
insert acctList;
insert acctList;
This is an equivalent example to the previous
one but it uses a method of the Database class instead of the DML verb.
// Create the list of sObjects to insert
List<Account> acctList = new
List<Account>();
acctList.add(new Account(Name='Acme1'));
acctList.add(new Account(Name='Acme2'));
// DML statement
Database.SaveResult[] sr = Database.insert(acctList, false);
// Iterate through each returned result
for (Database.SaveResult sr : srList) {
for (Database.SaveResult sr : srList) {
if (sr.isSuccess()) {
// Operation was
successful, so get the ID of the record that was processed
System.debug('Successfully inserted account. Account ID: ' + sr.getId());
}
else {
// Operation
failed, so get all errors
for(Database.Error err : sr.getErrors()) {
for(Database.Error err : sr.getErrors()) {
System.debug('The following error has occurred.');
System.debug(err.getStatusCode() + ': ' + err.getMessage());
System.debug('Account fields that affected this error: ' + err.getFields());
}
}
}
One difference between the two options
is that by using the Database class method, you can specify whether or not to
allow for partial record processing if errors are encountered. You can do so by
passing an additional second Boolean parameter. If you specify false for this
parameter and if a record fails, the remainder of DML operations can still
succeed. Also, instead of exceptions, a result object array (or one result
object if only one sObject was passed in) is returned containing the status of
each operation and any errors encountered. By default, this optional parameter
is true, which means that if at least one sObject can’t be processed, all
remaining sObjects won’t and an exception will be thrown for the record that
causes a failure.
The following helps you decide when you
want to use DML statements or Database class methods.
· Use DML statements if
you want any error that occurs during bulk DML processing to be thrown as
an Apex exception that immediately interrupts control flow (by
using try. . .catch blocks). This behavior is similar to the way exceptions are
handled in most database procedural languages.
·
Use Database class methods if you want
to allow partial success of a bulk DML operation—if a record fails, the
remainder of the DML operation can still succeed. Your application can then
inspect the rejected records and possibly retry the operation. When using this
form, you can write code that never throws DML exception errors. Instead, your
code can use the appropriate results array to judge success or failure. Note that
Database methods also include a syntax that supports thrown exceptions, similar
to DML statements.
Note
Most operations overlap between the
two, except for a few.
·
The convertLead operation is
only available as a Database class method, not as a DML statement.
The Database class also
provides methods not available as DML statements, such as methods transaction
control 
