Add a DAO for User objects and fix up the User DB object (#1765)

First, we create a sequence of User IDs in Postgres and assign it to the
User ID field, meaning that Hibernate can autogenerate IDs.

Next, add an update timestamp.

Next, add a constraint that we can't have multiple Users with the same
email address.

Finally, create a DAO since we'll usually want to query by that email
address (at least for now).

core/src/main/java/google/registry/model/console/User.java

@@ -22,10 +22,12 @@ import static google.registry.util.PasswordUtils.SALT_SUPPLIER;
 import static google.registry.util.PasswordUtils.hashPassword;
 import static google.registry.util.PreconditionsUtils.checkArgumentNotNull;
 
+import google.registry.model.BackupGroupRoot;
 import google.registry.model.Buildable;
-import google.registry.model.ImmutableObject;
 import javax.persistence.Column;
 import javax.persistence.Entity;
+import javax.persistence.GeneratedValue;
+import javax.persistence.GenerationType;
 import javax.persistence.Id;
 import javax.persistence.Index;
 import javax.persistence.Table;
@@ -37,10 +39,12 @@ import javax.persistence.Table;
       @Index(columnList = "gaiaId", name = "user_gaia_id_idx"),
       @Index(columnList = "emailAddress", name = "user_email_address_idx")
     })
-public class User extends ImmutableObject implements Buildable {
+public class User extends BackupGroupRoot implements Buildable {
 
   /** Autogenerated unique ID of this user. */
-  @Id private long id;
+  @Id
+  @GeneratedValue(strategy = GenerationType.IDENTITY)
+  private Long id;
 
   /** GAIA ID associated with the user in question. */
   @Column(nullable = false)
@@ -63,7 +67,7 @@ public class User extends ImmutableObject implements Buildable {
   /** Randomly generated hash salt. */
   String registryLockPasswordSalt;
 
-  public long getId() {
+  public Long getId() {
     return id;
   }
 

core/src/main/java/google/registry/model/console/UserDao.java

@@ -0,0 +1,57 @@
+// Copyright 2022 The Nomulus Authors. All Rights Reserved.
+//
+// Licensed under the Apache License, Version 2.0 (the "License");
+// you may not use this file except in compliance with the License.
+// You may obtain a copy of the License at
+//
+//     http://www.apache.org/licenses/LICENSE-2.0
+//
+// Unless required by applicable law or agreed to in writing, software
+// distributed under the License is distributed on an "AS IS" BASIS,
+// WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+// See the License for the specific language governing permissions and
+// limitations under the License.
+
+package google.registry.model.console;
+
+import static com.google.common.base.Preconditions.checkArgument;
+import static google.registry.persistence.transaction.TransactionManagerFactory.jpaTm;
+
+import java.util.Optional;
+
+/** Data access object for {@link User} objects to simplify saving and retrieval. */
+public class UserDao {
+
+  /** Retrieves the one user with this email address if it exists. */
+  public static Optional<User> loadUser(String emailAddress) {
+    return jpaTm()
+        .transact(
+            () ->
+                jpaTm()
+                    .query("FROM User WHERE emailAddress = :emailAddress", User.class)
+                    .setParameter("emailAddress", emailAddress)
+                    .getResultStream()
+                    .findFirst());
+  }
+
+  /** Saves the given user, checking that no existing user already exists with this email. */
+  public static void saveUser(User user) {
+    jpaTm()
+        .transact(
+            () -> {
+              // Check for an existing user (the unique constraint protects us, but this gives a
+              // nicer exception)
+              Optional<User> maybeSavedUser = loadUser(user.getEmailAddress());
+              if (maybeSavedUser.isPresent()) {
+                User savedUser = maybeSavedUser.get();
+                checkArgument(
+                    savedUser.getId().equals(user.getId()),
+                    String.format(
+                        "Attempted save of User with email address %s and ID %s, user with that"
+                            + " email already exists with ID %s",
+                        user.getEmailAddress(), user.getId(), savedUser.getId()));
+              }
+              jpaTm().put(user);
+            });
+  }
+}