4. More on CrudRepository

In the previous post, we used the CrudRepository interface. We only used the methods already provided by the interface. In this post, we look at how we can extend the interface with custom queries. Let's go back to our UserEndpoint. In the GET method, we can currently get the details of a user given his id. This is an impractical scenario. Most users' would not know what their id is. It is an internal identifier generated by our service and it makes no sense for our users.
Let's say we want to extend the existing GET/DELETE interface to allow query by id, username, and email address. Since we intend to query the table using the username and email columns, we need some kind of index on those columns. Since these fields are expected to be unique, we put a unique constraint in the @Table annotation.

When this change is deployed, the corresponding changes in database schema would be as below.

mysql> desc user;
+----------+--------------+------+-----+---------+-------+
| Field    | Type         | Null | Key | Default | Extra |
+----------+--------------+------+-----+---------+-------+
| id       | bigint(20)   | NO   | PRI | NULL    |       |
| email    | varchar(255) | YES  | UNI | NULL    |       |
| fullname | varchar(255) | YES  |     | NULL    |       |
| password | varchar(255) | YES  |     | NULL    |       |
| username | varchar(255) | YES  | UNI | NULL    |       |
+----------+--------------+------+-----+---------+-------+
5 rows in set (0.01 sec)
mysql> show create table user\G
*************************** 1. row ***************************
       Table: user
Create Table: CREATE TABLE `user` (
  `id` bigint(20) NOT NULL,
  `email` varchar(255) DEFAULT NULL,
  `fullname` varchar(255) DEFAULT NULL,
  `password` varchar(255) DEFAULT NULL,
  `username` varchar(255) DEFAULT NULL,
  PRIMARY KEY (`id`),
  UNIQUE KEY `uq_email` (`email`),
  UNIQUE KEY `uq_username` (`username`)
) ENGINE=MyISAM DEFAULT CHARSET=utf8
1 row in set (0.00 sec)

As we can see from the schema both the columns have unique constraints attached to them. The next step is to add methods in the UserRepository.java to query the user for a given username or email.

Now that we have all the required changes in place, we modify the UserEndpoint to handle the changes. We first create a private method retrieveUser which will retrieve a user from repository given an id, username or email.

In this method, we take an argument of type String, we first assume it to be the id if id fails we try with email and then with the username.

$ curl -X GET http://localhost:8080/user/jdoe@example.com
{"id":6,"fullname":"John Doe","username":"jdoe","password":"JohnDoe123","email":"jdoe@example.com"}

Here is the complete UserEndpoint class after modification.