Liquibase Preconditions changeLogPropertyDefined

Sometimes a common property is used multiple times in a ChangeLog file, so writing a common property in multiple places is redundant and error-prone. a good solution is to keep common property in one place and then refer from there so that if in the future, common property can be changed in one place and will be reflected everywhere.

some properties can be dynamic and can only pass at run time. Liqubase allows to dynamically substitute a property. a placeholder is defined on top and can be accessed later by using the ${property} syntax.

in the Below example, the table name is defined in a property at the top and is accessed in ChangeLog files.

<?xml version="1.1" encoding="UTF-8" standalone="no"?>
<databaseChangeLog xmlns="http://www.liquibase.org/xml/ns/dbchangelog" xmlns:ext="http://www.liquibase.org/xml/ns/dbchangelog-ext" xmlns:pro="http://www.liquibase.org/xml/ns/pro" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog-ext http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-ext.xsd http://www.liquibase.org/xml/ns/pro http://www.liquibase.org/xml/ns/pro/liquibase-pro-latest.xsd http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
	<property name="table.name" value="apple" />
	<changeSet author="wesome" id="1692599548266-1">
		<createTable catalogName="appledb" tableName="${table.name}">
			<column autoIncrement="true" name="apple_id" type="BIGINT">
				<constraints nullable="false" primaryKey="true" />
			</column>
			<column name="apple_name" type="VARCHAR(255)" />
			<column defaultValueComputed="CURRENT_TIMESTAMP" name="current_date_time" type="datetime" />
		</createTable>
	</changeSet>
	<changeSet author="wesome" id="1692599548266-2">
		<insert catalogName="appledb" tableName="apple">
			<column name="apple_id" />
			<column name="apple_name" value="Fuji" />
			<column name="current_date_time" valueDate="now()" />
		</insert>
	</changeSet>
</databaseChangeLog>

liquibase.properties (update changeLog File file format with SQL, XML, YAML, JSON as per changelog.mysql.)

changeLogFile=changelog.mysql.xml
liquibase.command.url:jdbc:mysql://localhost:3306/appleDb?createDatabaseIfNotExist=true&autoReconnect=true&useSSL=false&allowPublicKeyRetrieval=true
liquibase.command.username : root
liquibase.command.password : rootroot

Dynamic properties can be passed in multiple ways.

1. attribute to Liquibase runner.
2. As a JVM system property.
3. As an environment variable.
4. As a CLI attribute,
5. In the property element of the changelog file itself.

changeLogPropertyDefined is a Preconditions that checks if the property is defined before executing the changeset

<?xml version="1.1" encoding="UTF-8" standalone="no"?>
<databaseChangeLog xmlns="http://www.liquibase.org/xml/ns/dbchangelog" xmlns:ext="http://www.liquibase.org/xml/ns/dbchangelog-ext" xmlns:pro="http://www.liquibase.org/xml/ns/pro" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog-ext http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-ext.xsd http://www.liquibase.org/xml/ns/pro http://www.liquibase.org/xml/ns/pro/liquibase-pro-latest.xsd http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
	<property name="table.name" value="apple" />
	<changeSet author="wesome" id="1692599548266-1">
		<preConditions >
			<changeLogPropertyDefined property="table.name" />
		</preConditions>
		<createTable catalogName="appledb" tableName="${table.name}">
			<column autoIncrement="true" name="apple_id" type="BIGINT">
				<constraints nullable="false" primaryKey="true" />
			</column>
			<column name="apple_name" type="VARCHAR(255)" />
			<column defaultValueComputed="CURRENT_TIMESTAMP" name="current_date_time" type="datetime" />
		</createTable>
	</changeSet>
	<changeSet author="wesome" id="1692599548266-2">
		<insert catalogName="appledb" tableName="apple">
			<column name="apple_id" />
			<column name="apple_name" value="Fuji" />
			<column name="current_date_time" valueDate="now()" />
		</insert>
	</changeSet>
</databaseChangeLog>

liquibase.properties (update changeLog File file format with SQL, XML, YAML, JSON as per changelog.mysql.)

changeLogFile=changelog.mysql.xml
liquibase.command.url:jdbc:mysql://localhost:3306/appleDb?createDatabaseIfNotExist=true&autoReconnect=true&useSSL=false&allowPublicKeyRetrieval=true
liquibase.command.username : root
liquibase.command.password : rootroot

changeLogPropertyDefined provides an value attribute, that matches the value of dynamic property as well.

<?xml version="1.1" encoding="UTF-8" standalone="no"?>
<databaseChangeLog xmlns="http://www.liquibase.org/xml/ns/dbchangelog" xmlns:ext="http://www.liquibase.org/xml/ns/dbchangelog-ext" xmlns:pro="http://www.liquibase.org/xml/ns/pro" xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance" xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog-ext http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-ext.xsd http://www.liquibase.org/xml/ns/pro http://www.liquibase.org/xml/ns/pro/liquibase-pro-latest.xsd http://www.liquibase.org/xml/ns/dbchangelog http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-latest.xsd">
	<property name="table.name" value="apple" />
	<changeSet author="wesome" id="1692599548266-1">
		<preConditions>
			<changeLogPropertyDefined property="table.name" value="apple1" />
		</preConditions>
		<createTable catalogName="appledb" tableName="${table.name}">
			<column autoIncrement="true" name="apple_id" type="BIGINT">
				<constraints nullable="false" primaryKey="true" />
			</column>
			<column name="apple_name" type="VARCHAR(255)" />
			<column defaultValueComputed="CURRENT_TIMESTAMP" name="current_date_time" type="datetime" />
		</createTable>
	</changeSet>
	<changeSet author="wesome" id="1692599548266-2">
		<insert catalogName="appledb" tableName="apple">
			<column name="apple_id" />
			<column name="apple_name" value="Fuji" />
			<column name="current_date_time" valueDate="now()" />
		</insert>
	</changeSet>
</databaseChangeLog>

liquibase.properties (update changeLog File file format with SQL, XML, YAML, JSON as per changelog.mysql.)

changeLogFile=changelog.mysql.xml
liquibase.command.url:jdbc:mysql://localhost:3306/appleDb?createDatabaseIfNotExist=true&autoReconnect=true&useSSL=false&allowPublicKeyRetrieval=true
liquibase.command.username : root
liquibase.command.password : rootroot