Upgrading DB schema in Spring Boot projects

In this article we saw how to upgrade the DB schema in Spring Boot projects using the spring.jpa properties:

• spring.jpa.generate-ddl
• spring.jpa.hibernate.ddl-auto

There is, however, a far more powerful way to do the same upgrade. That is by using Liquibase.

• Add org.liquibase:liquibase-core to your classpath.
• Create a new changelog file (json):

 {
  "databaseChangeLog": [
    {
      "changeSet": {
        "id": "1",
        "author": "AUTHOR_NAME",
        "changes": [
          {
            "addColumn": {
              "columns": [
                {
                  "column": {
                    "name": "EMAIL",
                    "type": "VARCHAR(255)",
                    "defaultValue": email@email.com,
                    "constraints": {
                      "nullable": false
                    }
                  }
                }
              ],
              "schemaName": "MY_SHEMA_NAME",
              "tableName": "MY_TABLE_NAME"
            }
          }
        ]
      }
    }
  ]
}

• Run liquibase update (this will run automatically when you start your Spring Boot project (make sure you set the changelog's path correctly in application.properties (liquibase.change-log=classpath:db/changelog/db.changelog-master.json))

That was all. Schema upgraded. You may wish to run updateSQL first, to output the upgrade SQL in a file so that it can be inspected before applying it in the database.

Read more in the official Liquibase site.

Thymeleaf dropdown with selected option

Thymeleaf suggests dropdown creation as follows:

<select th:field="*{type}">
<option th:each="type : ${allTypes}"
             th:value="${type}"
             th:text="#{${'seedstarter.type.' + type}}">Wireframe
</option>
</select>

However, if you want to have a 'selected' option this would not work:

<select th:field="*{type}">
 <option th:each="type : ${allTypes}"
              th:value="${type}"
              th:text="#{${'seedstarter.type.' + type}}"
              th:selected="${myCondition}">Wireframe
</option>
</select>

Instead you should do:

<select name="type">
<option th:each="type : ${allTypes}"
             th:value="${type}"
             th:text="#{${'seedstarter.type.' + type}}"
             th:selected="${myCondition}">Wireframe
</option>
</select>

Sequence of characters separated by a delimiter and optionally starting with a supplied prefix and ending with a supplied suffix

If you have an array of Strings, say ["9", "30", "0"], and you wish to convert it to a String "[9, 30, 0]", do:

StringJoiner sj = new StringJoiner(",", "[", "]");
Arrays.asList(myArray).forEach(p -> sj.add(p));
sj.toString();

More about StringJoiner:
https://docs.oracle.com/javase/8/docs/api/java/util/StringJoiner.html