Loan externalId unique validation

fineract-provider/src/main/java/org/apache/fineract/portfolio/loanaccount/domain/LoanRepository.java

@@ -161,4 +161,6 @@ public interface LoanRepository extends JpaRepository<Loan, Long>, JpaSpecificat
     @Query(FIND_BY_ACCOUNT_NUMBER)
     Loan findLoanAccountByAccountNumber(@Param("accountNumber") String accountNumber);
 
+    boolean existsByExternalId(@Param("externalId") String externalId);
+
 }

fineract-provider/src/main/java/org/apache/fineract/portfolio/loanaccount/domain/LoanRepositoryWrapper.java

@@ -240,6 +240,10 @@ public class LoanRepositoryWrapper {
         return this.repository.findNonClosedLoanByAccountNumber(accountNumber);
     }
 
+    public boolean existLoanByExternalId(final String externalId) {
+        return this.repository.existsByExternalId(externalId);
+    }
+
     // Looks like we need complete entity
     @Transactional(readOnly = true)
     public Loan findNonClosedLoanThatBelongsToClient(@Param("loanId") Long loanId, @Param("clientId") Long clientId) {

fineract-provider/src/main/java/org/apache/fineract/portfolio/loanaccount/service/LoanApplicationWritePlatformServiceJpaRepositoryImpl.java

@@ -303,6 +303,16 @@ public class LoanApplicationWritePlatformServiceJpaRepositoryImpl implements Loa
 
             this.fromApiJsonDeserializer.validateForCreate(command.json(), isMeetingMandatoryForJLGLoans, loanProduct);
 
+            // Validate If the externalId is already registered
+            final String externalId = this.fromJsonHelper.extractStringNamed("externalId", command.parsedJson());
+            if (StringUtils.isNotBlank(externalId)) {
+                final boolean existByExternalId = this.loanRepositoryWrapper.existLoanByExternalId(externalId);
+                if (existByExternalId) {
+                    throw new GeneralPlatformDomainRuleException("error.msg.loan.with.externalId.already.used",
+                            "Loan with externalId is already registered.");
+                }
+            }
+
             final List<ApiParameterError> dataValidationErrors = new ArrayList<>();
             final DataValidatorBuilder baseDataValidator = new DataValidatorBuilder(dataValidationErrors).resource("loan");