Course initial

Description

Closes #187 (closed), #183 (closed) A working backend support for courses. This includes a new repository and controller which manages the courses.

A course has the following structure (when serialized):

{
    "id": "5cf028357fc2582206be877b",
    "name": "Complexity Theory",
    "courseCode": "TI3306",
    "year": 2019,
    "instructorSet": [],
    "taSet": [
        "ta"
    ],
    "assignmentIds": [
        "5ce653c5ff1dbf1ab679583d"
    ]
} 

The following actions can be performed

• Retrieve the list of all courses
• Add a new course
• Add an assignment to a course
• Add a user to a course (with proper authentication)

Changes

• Refactored the getUser method to return an optional
• General refactoring of the DatabaseConnection to not throw more sensible exceptions (e.g. when a user cannot be found)

Additions

• A CourseRepository, Course and CourseController

Test and Review

To be filled in by the reviewers

• All of the methods are commented to expectation

• The methods are tested to satisfaction

• There are no unnecessary files present in the MR

• The continuous integration has no problems with the MR

• The MR is filled in as requested (including labels, milestones, and reviewers)

• The documentation is up-to-date

• All nullable parameters are marked as such

core/src/main/java/nl/tudelft/ewi/auta/core/authentication/DatabaseConnection.java

@@ -9,7 +9,9 @@ import java.util.ArrayList;
 import java.util.Collection;
 import java.util.HashSet;
 import java.util.List;
+import java.util.Optional;
 
+import nl.tudelft.ewi.auta.core.response.exception.DuplicateUserException;
 import org.springframework.data.domain.Page;
 import org.springframework.data.domain.PageImpl;
 import org.springframework.data.domain.PageRequest;
@@ -48,8 +50,13 @@ public class DatabaseConnection implements AutoCloseable {
      * Creates a new user.
      * @param user the user
      * @throws SQLException if the SQL goes wrong
+     * @throws DuplicateUserException if the user already exists
      */
     public void register(final User user) throws SQLException {
+        final var username = user.getUsername();
+        if (this.hasUser(username)) {
+            throw new DuplicateUserException("User with username " + username + " already exists");
+        }
         try (var userStatement = this.connection.prepareStatement(
                 "INSERT INTO users (username, password, enabled) values (?, ?, ?)"
         ); var authStatement = this.connection.prepareStatement(
@@ -112,7 +119,7 @@ public class DatabaseConnection implements AutoCloseable {
      * @return the user
      * @throws SQLException if the SQL goes wrong
      */
-    public User getUser(final String username) throws SQLException {
+    public Optional<User> getUser(final String username) throws SQLException {
         try (var userStatement = this.connection.prepareStatement(
                   "SELECT users.password, users.enabled, authorities.authority "
                 + "  FROM users "
@@ -122,15 +129,17 @@ public class DatabaseConnection implements AutoCloseable {
         )) {
             userStatement.setString(1, username);
             try (var userRes = userStatement.executeQuery()) {
+                if (!userRes.next()) {
+                    return Optional.empty();
+                }
                 final var password = userRes.getString("password");
                 final var enabled = userRes.getBoolean("enabled");
-
                 final var authorities = new HashSet<GrantedAuthority>();
-                while (userRes.next()) {
+                do {
                     authorities.add(new SimpleGrantedAuthority(userRes.getString("authority")));
-                }
-
-                return new User(username, password, enabled, true, true, true, authorities);
+                } while (userRes.next());
+                return Optional.of(new User(username, password, enabled, true, true, true,
+                        authorities));
             }
         }
     }