<changeSet id="1" author="nvoxland">
<createTable tableName="company">
<column name="address" type="varchar(255)"/>
</createTable>
</changeSet>Talking to a relational database with Clojure is relatively easy. There’s a great library next.jdbc for that. In legacy applications, you may encounter an older library, clojure.java.jdbc.
Liquibase is a well-know tool for tracking, versioning, and deploying database schema changes.
It uses changelog files to list database changes in the form of changesets (SQL, XML, YAML, JSON), which consists of Change Types. Standard changsets use SQL or a DB-agnostic equivalent written in XML, YAML, or JSON.
Here’s an example of a very simple changset adding a new table with a single column:
<changeSet id="1" author="nvoxland">
<createTable tableName="company">
<column name="address" type="varchar(255)"/>
</createTable>
</changeSet>Sometimes, there’s a more complicated migration that’s very difficult or impossible to express in SQL (or its Xml/YAML/JSON equivalent). That is, you need to write actual code to perform the migration. In that case, Liquibase offers customChange Change Type.
To implement a custom migration you need to:
Create a Java class that implements the liquibase.change.custom.CustomSqlChange or liquibase.change.custom.CustomTaskChange interface
(showing only a subset of methods here):
public class ExampleCustomTaskChange implements CustomTaskChange, CustomTaskRollback {
private String helloTo;
@SuppressWarnings({"UnusedDeclaration", "FieldCanBeLocal"})
private ResourceAccessor resourceAccessor;
@Override
public void execute(Database database) throws CustomChangeException {
Scope.getCurrentScope().getLog(getClass()).info("Hello "+getHelloTo());
}
@Override
public void rollback(Database database) throws CustomChangeException, RollbackImpossibleException {
Scope.getCurrentScope().getLog(getClass()).info("Goodbye "+getHelloTo());
}
...
}Compile the created class, package it into a JAR file, and then add it to a Liquibase classpath.
Reference the class in your changelog:
...
<changeSet id="21" author="nvoxland">
<customChange class="liquibase.change.custom.ExampleCustomTaskChange">
<param name="helloTo" value="world"/>
</customChange>
</changeSet>
...Persuading your ssh client to use one and only one SSH key may be tricky. In any case, it may help to understand what keys/identities are actually used when you connect to the remote host.
Here’s a small Keyboard Maestor macro I made today:
This is gonna be a rather short and trivial post but I wanted to share it anyway because it can be useful, ocassionally.