Implementation of scenario 7

Author: bwajtr

src/main/java/com/clevergang/dbtests/Scenarios.java

@@ -110,8 +110,20 @@ public void scenarioSix() {
         logger.info("Department {} is in the {} company", softwareDevelopmentDepartment.getName(), company.getName());
     }
 
+    /**
+     * Fetch one-to-many relation (Departments for Company)
+     */
     public void scenarioSeven() {
+        Company company = repository.findCompany(1);
+
+        // For one-to-many relations the situation is quite similar to many-to-one relations (scenario six). In JPA this
+        // is "easy" - you define @OneToMany relation in the Company entity and then you just call getDepartments() method ->
+        // a lazy select is issued and Departments are fetched from DB. However you can also use EAGER FetchType strategy which
+        // causes the relation to load along with the primary entity - this behavior is (by our opinion) the source of all evil
+        // in JPA... So, in non-JPA approach, we don't have any "eager" loads, just explicit calls for data:
+        List<Department> departments = repository.getDepartmentsForCompany(company.getPid());
 
+        logger.info("There are {} departments in {} company", departments.size(), company.getName());
     }
 
     public void scenarioEight() {

src/main/java/com/clevergang/dbtests/repository/DataRepository.java

@@ -8,6 +8,10 @@
 import com.clevergang.dbtests.model.Project;
 
 /**
+ * In "normal" application we would rather split the repository to multiple classes based on entity
+ * we want to work with (CompanyRepository, DepartmentRepository etc.). We decided
+ * to create just a single interface in this project, so different implementations are more easily compared...
+ *
  * @author Bretislav Wajtr <bretislav.wajtr@clevergang.com>
  */
 public interface DataRepository {
@@ -23,4 +27,6 @@ public interface DataRepository {
     List<Integer> insertAllProjects(List<Project> projects);
 
     void updateEmployee(Employee employeeToUpdate);
+
+    List<Department> getDepartmentsForCompany(Integer pid);
 }

src/main/java/com/clevergang/dbtests/repository/impl/jdbctemplate/JDBCDataRepositoryImpl.java

@@ -138,4 +138,16 @@ public void updateEmployee(Employee employeeToUpdate) {
 
         jdbcTemplate.update(updateStatement, params);
     }
+
+    @Override
+    public List<Department> getDepartmentsForCompany(Integer pid) {
+        String query = "SELECT pid, company_pid, name" +
+            "           FROM department " +
+            "           WHERE company_pid = :pid";
+
+        Map<String, Object> params = new HashMap<>();
+        params.put("pid", pid);
+
+        return jdbcTemplate.query(query, params, new BeanPropertyRowMapper<>(Department.class));
+    }
 }

src/main/java/com/clevergang/dbtests/repository/impl/jooq/JooqDataRepositoryImpl.java

@@ -126,5 +126,13 @@ public void updateEmployee(Employee employeeToUpdate) {
             .execute();
     }
 
+    @Override
+    public List<Department> getDepartmentsForCompany(Integer pid) {
+        return create.
+            selectFrom(DEPARTMENT)
+            .where(DEPARTMENT.COMPANY_PID.eq(pid))
+            .fetchInto(Department.class);
+    }
+
 }