Constraints in liquibase - liquibase

Question

<?xml version="1.0" encoding="UTF-8"?>
<databaseChangeLog
xmlns="http://www.liquibase.org/xml/ns/dbchangelog"
xmlns:xsi="http://www.w3.org/2001/XMLSchema-instance"
xsi:schemaLocation="http://www.liquibase.org/xml/ns/dbchangelog
http://www.liquibase.org/xml/ns/dbchangelog/dbchangelog-3.8.xsd">
<changeSet id="0.1.1.0" author="Bob" failOnError="true">
<createTable tableName="roles">
<column name="id" type="bigint" autoIncrement="true">
<constraints primaryKey="true"/>
</column>
<column name="name" type="varchar(1024)">
<constraints nullable="false" unique="true"/>
</column>
<column name="fam" type="varchar(1024)">
<constraints nullable="false"/>
</column>
</createTable>
<rollback>
</rollback>
I have such migrations to create a table, now I have changes and need to make other migrations. In the table, the name field is unique, I should get rid of this, that is, the name should not be unique and I need to impose a restriction on the fam. One fam should not be assigned to two roles with the same name. But roles with different names can contain the same fam. thanks in advance

Answer 1

If you want to add changes to the existing schema, you should keep your existing changes the way they are and write new changeSets.
So in order to implement requirement
the name field is unique, I should get rid of this
you could have used <dropUniqueConstraint> change, but it requires a constraintName attribute. But you didn't provide a uniqueConstraintName for the name's unique constraint when you were creating it, which makes implementation tricky. it's always a good practice to give your constraints and indexes names.
So, you may do the following:
create a new column, e.g. non_unique_name
copy all the data from name to non_unique_name
drop name column
rename non_unique_name column to name
The changeSets could look like this:
<changeSet id="0.1.1.1" author="Bob">
<preConditions onFail="MARK_RAN">
<tableExists tableName="roles"/>
<not>
<columnExists tableName="roles" columnName="non_unique_name"/>
</not>
</preConditions>
<comment>create a new column, e.g. non_unique_name</comment>
<addColumn tableName="roles">
<column name="non_unique_name" type="varchar(1024)">
<constraints nullable="false"/>
</column>
</addColumn>
</changeSet>
<changeSet id="0.1.1.2" author="Bob">
<preConditions onFail="MARK_RAN">
<tableExists tableName="roles"/>
<columnExists tableName="roles" columnName="non_unique_name"/>
<columnExists tableName="roles" columnName="name"/>
</preConditions>
<comment>copy all the data from name to non_unique_name</comment>
<update tableName="roles">
<column name="non_unique_name" valueComputed="name"/>
</update>
</changeSet>
<changeSet id="0.1.1.3" author="Bob">
<preConditions onFail="MARK_RAN">
<tableExists tableName="roles"/>
<columnExists tableName="roles" columnName="name"/>
</preConditions>
<comment>drop name column</comment>
<dropColumn tableName="roles" columnName="name"/>
</changeSet>
<changeSet id="0.1.1.4" author="Bob">
<preConditions onFail="MARK_RAN">
<tableExists tableName="roles"/>
<columnExists tableName="roles" columnName="non_unique_name"/>
</preConditions>
<comment>rename non_unique_name column to name</comment>
<renameColumn tableName="roles" oldColumnName="non_unique_name" newColumnName="name"
columnDataType="varchar(1024)"/>
</changeSet>
And in order to implement the requirement:
One dealer should not be assigned to two roles with the same name. But
roles with different names can contain the same dealer.
You may use <addUniqueConstraint> change, with it you can add composite unique constraints. The changeSet could look like this:
<changeSet id="0.1.1.5" author="Bob">
<preConditions onFail="MARK_RAN">
<tableExists tableName="roles"/>
<columnExists tableName="roles" columnName="dealer"/>
<columnExists tableName="roles" columnName="name"/>
</preConditions>
<comment>add unique constraint for roles.dealer and roles.name</comment>
<addUniqueConstraint tableName="roles" columnNames="dealer, name"
constraintName="roles_dealer_name_unique" />
</changeSet>