MyBatis - defining a global parameter

问题:

First the problem: I'm using XML-defined queries and the SQL contains database name as part of a table name. For example: SELECT * from mydb.bar. Unfortunately, databases are created/named all over the place and mudb part is really dynamic and can change at any moment. So I wanted to replace it with a property so it would look like SELECT * FROM ${dbname}.bar and then I defined the following section in mybatis-config.xml:

<properties>
    <property name="dbname" value="mydb"/>
</properties>

But when I run the query ${dbname} evaluates to null. Same happens if I define this property in the properties file. I would hate to pass this as part of the each call parameters since this is truly a global property. Can this be done? And if yes - how?

回答1:

Yes, you can! This is kind of a weird undocumented feature maybe. When building your Configuration object, do something like this. (org.apache.ibatis.session.Configuration)

configuration.getVariables().put("global_param", "123");

Then in your XML map, you can reference.

    select * from ${global_param}

回答2:

I had the same issue using Spring+MyBatis, and solved it by setting 'configurationProperties' using my Spring XML definition for sqlSessionFactory. My example below shows how to set a custom global property named 'encryptionKey', with a value which you can either hard-code in the XML file, or load from an external file using the context:property-placeholder tag (as below).

<context:property-placeholder location="/WEB-INF/spring/config-datasource.properties" />

<beans:bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
    <beans:property name="dataSource" ref="dataSource" />
    <beans:property name="typeAliasesPackage" value="com.example.model" />
    <beans:property name="configurationProperties">
        <beans:props>
            <beans:prop key="encryptionKey">${jdbc.encryptionKey}</beans:prop>
        </beans:props>
    </beans:property>
</beans:bean>

回答3:

I was using an XML configuration but not Spring and set a property inside the Configuration object but discovered that had to be done before the mapper files are loaded (see here). I abandoned the Configuration object approach and went with this approach, which worked for me:

  Reader reader = Resources.getResourceAsReader("..../mybatis-config.xml");
  Properties properties = new Properties();
  properties.setProperty("dbname", "mydb");
  SqlSessionFactory.factory = new SqlSessionFactoryBuilder().build(reader, "development", properties);

Then, as Andy Pryor posted, use select * from ${dbname} in the XML mapper.