1. Generate Change Logs from an existing database
Generate change logs from an existing database. For instance, copy postgresSQL driver to %LINQUIBASE_HOME%/postgresql-8.3-603.jdbc3.jar. Run a following line command in console (single line).
java -jar liquibase.jar --classpath=postgresql-8.3-603.jdbc3.jar --driver=org.postgresql.Driver --changeLogFile=./structure.xml --url="jdbc:postgresql://abc.com:5432/store_db" --username=postgres --password=1234 generateChangeLog
If successful, liquibase will show a message “Liquibase ‘generateChangeLog’ Successful”
2. Check a table already presents
Using preCondition tag which follows some form of boolean evaluation to check a table exists. For example, not(tableExists) = not(true) = false, therefore the createTable would not execute.
<changeSet id="1" author="Khiem.Truong">
<preConditions onFail="MARK_RAN">
<not>
<tableExists tableName="trading"></tableExists>
</not>
</preConditions>
<createTable tableName="trading">
<column name="code" autoIncrement="true" type="BIGINT">
<constraints nullable="false" primaryKey="true"/>
</column>
...
</createTable>
</changeSet>
3. Insert a record to database.
Similarly, if the select query below >= 1, sqlCheck will return false and raise onFail
<changeSet id="9" author="Khiem.Truong">
<preConditions onFail="MARK_RAN">
<sqlCheck expectedResult="0">select count(*) from id_code_data
where symbol='gbst' and assigned_prefix='NAS'</sqlCheck>
</preConditions>
<insert tableName="id_code_data">
<column name="symbol" value="gbst"/>
<column name="name" value="Global banking settlement transaction"/>
<column name="assigned_prefix" value="NAS"/>
</insert>
</changeSet>
4. Change datatype.
A column updates to a new datatype if it already exists. Otherwise, the changeSet is ignore.
<changeSet id="change_eicc_sub_section_label" author="Khiem.Truong">
<preConditions onFail="MARK_RAN">
<columnExists tableName="id_code_data" columnName="name"/>
</preConditions>
<modifyDataType tableName="id_code_data" columnName="name" newDataType="text" />
</changeSet>
References:
- Liquibase | Database Refactoring | Preconditions. Accessed at http://www.liquibase.org/documentation/preconditions.html on Oct 13, 2016
- Generating change logs. Accessed at http://www.liquibase.org/documentation/generating_changelogs.html on Oct 13, 2016