LiquiBase预判断

预判断解决的问题：运行liquibase之前，DB中已经存在一个table，所以需要加上预判断；

完整的一个例子：

<?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-3.1.xsd">

    <property name="now" value="now()" dbms="mysql,h2"/>

    <property name="now" value="current_timestamp" dbms="postgresql"/>

    <property name="now" value="sysdate" dbms="oracle"/>

     

    <changeSet id="20151108112500" author="WWW">

<!-- 预判断-->

        <preConditions onFail="MARK_RAN">

            <not>

                <tableExists tableName="MYTABLE"/>

            </not>

        </preConditions>

        <createTable tableName="MYTABLE">

           <column name="id" type="bigint" autoIncrement="true">

                <constraints primaryKey="true" nullable="false"/>

            </column>

            <column name="title" type="varchar(100)"/>

            <column name="content" type="text">

                <constraints nullable="false" />

            </column>

            <column name="course_id" type="bigint"/>

            <column name="chapter_id" type="varchar(40)"/>

            <column name="user_id" type="bigint">

                 <constraints nullable="false" />

            </column>

             <column name="reply_count" type="int"/>

             <column name="same_ask_count" type="int"/>

             <column name="browse_count" type="int"/>

             <column name="time" type="bigint"/>

            <column name="status" type="varchar(10)"/>

            <column name="created_by" type="varchar(50)">

                <constraints nullable="false"/>

            </column>

            <column name="created_date" type="timestamp" defaultValueDate="${now}">

                <constraints nullable="false"/>

            </column>

            <column name="last_modified_by" type="varchar(50)"/>

            <column name="last_modified_date" type="timestamp"/>

        </createTable>

    </changeSet>

</databaseChangeLog>