multiple ds springboot

Author: msdalp

_posts/2019-10-12-Multiple-Datasources-with-Spring-Boot-and-Hibernate.markdown

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+---
+layout: post
+title:  "Multiple Datasources with Spring Boot and Hibernate"
+date:   2019-10-12 12:00:00
+categories:
+---
+
+Adding two database connection to a Spring Boot application is quite straightforward unless you are using `JpaRepositories`. Simple task of adding urls and giving JdbcTemplate different identifier names become an annoying task.
+
+Starting with adding configurations of two different Datasource to the project: 
+
+{% highlight yaml %}
+app.datasource.backup.url=jdbc:mysql://backup_db
+app.datasource.backup.username=user
+app.datasource.backup.password=password
+app.datasource.backup.maximum-pool-size=10
+
+app.datasource.main.url=jdbc:mysql://main_db
+app.datasource.main.username=user
+app.datasource.main.password=password
+app.datasource.main.maximum-pool-size=10
+{% endhighlight %}
+
+These will be used for datasource creation initially and later identifiers will be enough. 
+
+{% highlight java %}
+    @Bean
+    @Primary
+    @ConfigurationProperties("app.datasource.main")
+    public DataSourceProperties mainDataSourceProperties() {
+        return new DataSourceProperties();
+    }
+
+    @Bean(name = "dbMain")
+    @Primary
+    public DataSource mainDataSource() {
+        return mainDataSourceProperties().initializeDataSourceBuilder().build();
+    }
+
+    @Bean(name = "jdbcMain")
+    @Autowired
+    public JdbcTemplate mainJdbcTemplate(@Qualifier("dbMain") DataSource dsMain) {
+        return new JdbcTemplate(dsMain);
+    }
+
+
+    @Bean(name = "jdbcBackup")
+    @Autowired
+    public JdbcTemplate slaveJdbcTemplate(@Qualifier("dbBackup") DataSource dsSlave) {
+        return new JdbcTemplate(dsSlave);
+    }
+
+    @Bean
+    @ConfigurationProperties("app.datasource.backup")
+    public DataSourceProperties backupDataSourceProperties() {
+        return new DataSourceProperties();
+    }
+
+
+    @Bean(name = "dbBackup")
+    public DataSource backupDataSource() {
+        return backupDataSourceProperties().initializeDataSourceBuilder().build();
+    }
+{% endhighlight %}
+
+In a configuration file or in the SpringBoot main class define these datasource beans. 
+* Read configuration information for resources
+* Create a datasource with a name from that configuration
+* Set the datasource created to a JdbcTemplate. The name given here will be used for accessing to the different JdbcTemplate beans as `@Qualifier("jdbcMain") JdbcTemplate jdbcTemplate`
+
+While defining a jdbc repository give the identifier to access a specific database. 
+
+{% highlight java %}
+@Repository
+public class GameRepository {
+
+    private final JdbcTemplate jdbcTemplate;
+
+    @Autowired
+    public GameRepository(@Qualifier("jdbcMain") JdbcTemplate jdbcTemplate) {
+        this.jdbcTemplate = jdbcTemplate;
+    }
+    ...
+{% endhighlight %}
+
+What if we want to use JPA and define our objects with `Entity`. Datasource definitions and initialization will not change. However different `EntityManagers` and `TransactionManagers` must be defined.