postgresql - How can I create triggers for a postgreSQL db using liquibase?

Question

I'm using the dropwizard-migrations module for liquibase db refactoring. See the guide here: http://dropwizard.codahale.com/manual/migrations/

When I run java -jar my_project.jar db migrate my_project.yml

I get the following error:

ERROR [2013-09-11 20:53:43,089] liquibase: Change Set migrations.xml::11::me failed. Error: Error executing SQL CREATE OR REPLACE TRIGGER add_current_date_to_my_table BEFORE UPDATE ON my_table FOR EACH ROW EXECUTE PROCEDURE change_update_time();: ERROR: syntax error at or near "TRIGGER" Position: 19

Here are some relevant changesets from my migrations.xml file:

<changeSet id="1" author="me">
    <createProcedure>
        CREATE OR REPLACE FUNCTION change_update_time() RETURNS trigger
        LANGUAGE plpgsql
        AS $$
        BEGIN
        NEW.updated_at := CURRENT_TIMESTAMP;
        RETURN NEW;
        END;
        $$;
    </createProcedure>
    <rollback>
        DROP FUNCTION change_update_time();
    </rollback>
</changeSet>        

<changeSet id="2" author="me">
    <preConditions>
        <not>
            <tableExists tableName="my_table"/>
        </not>
    </preConditions>

    <createTable tableName="my_table">
        <column name="_id" type="integer" defaultValue="0">
            <constraints nullable="false"/>
        </column>
        <column name="updated_at" type="timestamp without time zone" defaultValue="now()">
            <constraints nullable="false"/>
        </column>
    </createTable>
</changeSet>

<changeSet id="3" author="me">
    <sql splitStatements="false">
        CREATE OR REPLACE TRIGGER add_current_date_to_my_table BEFORE UPDATE ON my_table FOR EACH ROW EXECUTE PROCEDURE change_update_time();
    </sql>
    <rollback>
        DROP TRIGGER add_current_date_to_my_table ON my_table;
    </rollback>
</changeSet>

Is there any way I can create the trigger add_current_date_to_my_table? Is this redundant with the "RETURNS trigger" from creating the function?

Answer 1

解决方案是：

<changeSet id="3" author="me">
    <sql>
        DROP TRIGGER IF EXISTS add_current_date_to_my_table ON my_table;
        CREATE TRIGGER add_current_date_to_my_table BEFORE UPDATE ON my_table FOR EACH ROW EXECUTE PROCEDURE change_update_time();
    </sql>
    <rollback>
        DROP TRIGGER add_current_date_to_my_table ON my_table;
    </rollback>
</changeSet>

H/T 延斯。

Answer 2

Ann Kilzer 提供了正确的答案，因为 Postgres 中没有CREATE OR REPLACE语句，这与 PL/SQL 不同。

所以我们需要把这条语句拆分成2个原子操作：

1. DROP TRIGGER
2. CREATE TRIGGER