Fixes ConcurrentModificationException in removeEmployee

A ConcurrentModificationException is raised when removing an
item from projectAssignments during its iteration. In order to
avoid this, a copy of the collection is made to iterate over it.

src/main/java/dgpena/siexample/persistence/Project.java

@@ -72,7 +72,9 @@ public class Project {
 	}
 
 	public void removeEmployee(Employee e) {
-		for (ProjectAssignment pa: this.projectAssignments) {
+		// create a copy of the this.projectAssignments in order to avoid ConcurrentModificationException
+		Set<ProjectAssignment> projectAssignmentsCopy = new HashSet(this.projectAssignments);
+		for (ProjectAssignment pa: projectAssignmentsCopy) {
 			if (pa.getEmployee().equals(e)) {
 				// this will call internalRemoveProjectAssignment
 				pa.setProject(null);
@@ -83,6 +85,7 @@ public class Project {
 	}
 
 	void internalRemoveProjectAssignment(ProjectAssignment projectAssignment) {
+		System.err.println("====>internal remove project assingment");
 		this.projectAssignments.remove(projectAssignment);
 	}
 

src/test/java/dgpena/siexample/persistence/ProjectsTest.java

@@ -77,9 +77,16 @@ public class ProjectsTest extends SQLBasedTest {
 		// insert an employee previously with JDBC
 		int employeeId = insertAnEmployee();
 
-		// assign the employee to the project (which should be removed due to CascadeType.REMOVE
-		// in Project.projectAssignments)
+		// insert a second employee previously with JDBC (this is the employee that will be removed from the project)
+		int employeeId2 = insertAnEmployee();
+
+
+		// assign those employees to the project
 		Statement statement = jdbcConnection.createStatement();
+		statement.executeUpdate("INSERT INTO ProjectAssignment(project_id, employee_id) values("+projectId+", "
+				+employeeId2+")", Statement
+				.RETURN_GENERATED_KEYS);
+		statement = jdbcConnection.createStatement();
 		statement.executeUpdate("INSERT INTO ProjectAssignment(project_id, employee_id) values("+projectId+", "
 				+employeeId+")", Statement
 				.RETURN_GENERATED_KEYS);
@@ -88,16 +95,16 @@ public class ProjectsTest extends SQLBasedTest {
 
 		em.getTransaction().begin();
 			Project p = new Projects(em).findById(projectId);
-			Employee e = new Employees(em).findById(employeeId);
+			Employee e = new Employees(em).findById(employeeId2);
 
 			p.removeEmployee(e);
 		em.getTransaction().commit();
 
 
-		// ensure that the project assignment does not exist
+		// ensure that the project assignment for employee 2 does not exist
 		statement = jdbcConnection.createStatement();
 		ResultSet res = statement.executeQuery("SELECT COUNT(*) as total from ProjectAssignment where employee_id = " +
-				""+employeeId+" and project_id = "+projectId);
+				""+employeeId2+" and project_id = "+projectId);
 		res.next();
 		assertEquals(0, res.getInt("total"));
 	}