[FIXED] I'm getting error when i tried List<Entity> to Dto with MapStruct

Issue

public class Account {

    private String accountId
    private List<Transaction> transactions = new ArrayList<>();

---

public abstract class Transaction {
    private double amount;

---

public class AccountEntity extends BaseEntity{
    @OneToMany
    private List<TransactionEntity> transactions;

---

public class TransactionEntity extends BaseEntity{
    @Id
    private String transactionId;
    private double amount;
    private String type;

    @ManyToOne
    @JoinColumn(name = "accountId", referencedColumnName = "accountNumber")
    private AccountEntity account;

---

@Mapper(componentModel = "spring")
public interface AccountMapper {
    
    Account AccountEntityToAccount(AccountEntity accountEntity);

    AccountEntity AccountToAccountEntity(Account account);

My AccountEntityToAccount method is getting error which is The return type Transaction is an abstract class or interface. Provide a non abstract / non interface result type or a factory method. Account AccountEntityToAccount(AccountEntity accountEntity);

how could i solve this problem. My Transaction class should be abstract i can not change abstract keyword

Solution

Add a method to create the correct Transaction from the TransactionEntity supplied.

Reading the code you probably want to have something like the following:

Transaction fromTransactionEntity(TransactionEntity entity){
  if (entity == null){
    return null;
  }
  if ( entity.getType().equals("something") ) {
    return toSomethingTransaction(entity);
  }
  if ( entity.getType().equals("other") ) {
    return toOtherTransaction(entity);
  }
  throw new IllegalStateException("unsupported transaction found, cannot instantiate object.");
}

SomethingTransaction toSomethingTransaction(TransactionEntity entity);

OtherTransaction toOtherTransaction(TransactionEntity entity);

In the other direction you probably want to do the same thing. (when 1.5.0 is released you can use @SubclassMapping for this instead of manually writing the instanceof. currently at 1.5.0.RC1 stage.)

TransactionEntity toTransactionEntity(Transaction transaction){
  if (transaction == null){
    return null;
  }
  if (transaction instanceof SomethingTransaction){
    return fromSomethingTransaction(transaction);
  }
  if (transaction instanceof OtherTransaction){
    return toOtherTransaction(entity);
  }
  throw new IllegalStateException("unsupported transaction found, cannot store it.");
}

@Mapping( target = "type", constant = "something" )
TransactionEntity fromSomethingTransaction(SomethingTransaction transaction);

@Mapping( target = "type", constant = "other" )
TransactionEntity fromOtherTransaction(OtherTransaction transaction);

Answered By - Ben Zegveld
Answer Checked By - Cary Denson (JavaFixing Admin)