MyBatis DB_VENDOR doesn't work - spring

Question

can you please help me figure out what is wrong with the DB_VENDOR in MyBatis? I'm using mybatis 3.4.2, mybatis-spring 1.3.1, spring 4.3.6.RELEASE.
Everything, but the vendor dependent queries, works fine. The example query is not vendor dependent, this is only for the sake of this example. If I remove the databaseId attribute from it and remove the duplicated one, this query works.
I need to support Oracle and PostgreSQL and have already checked the metadata getDatabaseProductName() directly within my test scope, getting "Oracle" and "PostgreSQL". So if I got the documentation right, it should work, shouldn't it?
All I get with the databaseId in place is:
org.apache.ibatis.binding.BindingException: Invalid bound statement (not found): mappers.ConfigurationMapper.containsKey
test-mybatis-config.xml:
<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE configuration PUBLIC "-//mybatis.org//DTD Config 3.0//EN" "Http://mybatis.org/dtd/mybatis-3-config.dtd">
<configuration>
<databaseIdProvider type="DB_VENDOR">
<property name="PostgreSQL" value="postgres"/>
<property name="Oracle" value="oracle"/>
</databaseIdProvider>
<mappers>
<mapper resource="mybatis/ConfigurationMapper.xml"/>
</mappers>
</configuration>
test-context.xml (having another one with PostgreSQL datasource)
<mybatis:scan base-package="mappers" annotation="org.apache.ibatis.annotations.Mapper" factory-ref="sqlSessionFactory"/>
<bean id="dataSource" class="org.springframework.jdbc.datasource.DriverManagerDataSource">
<property name="driverClassName" value="oracle.jdbc.OracleDriver"/>
<property name="url" value="jdbc:oracle:thin:#localhost:1521:XE"/>
<property name="username" value="test"/>
<property name="password" value="test"/>
</bean>
<bean class="org.mybatis.spring.SqlSessionFactoryBean" id="sqlSessionFactory">
<property name="dataSource" ref="dataSource"/>
<property name="configLocation" value="classpath:test-mybatis-config.xml"/>
</bean>
<bean id="transactionManager" class="org.springframework.jdbc.datasource.DataSourceTransactionManager">
<property name="dataSource" ref="dataSource"/>
</bean>
ConfigurationMapper.xml
<?xml version="1.0" encoding="UTF-8" ?>
<!DOCTYPE mapper PUBLIC "-//mybatis.org//DTD Mapper 3.0//EN" "http://mybatis.org/dtd/mybatis-3-mapper.dtd">
<mapper namespace="mappers.ConfigurationMapper">
<select id="containsKey" resultType="string" parameterType="string" databaseId="oracle">
SELECT '1' AS test FROM config_keys WHERE key = #{configKey}
</select>
<select id="containsKey" resultType="string" parameterType="string" databaseId="postgres">
SELECT '1' AS test FROM config_keys WHERE key = #{configKey}
</select>
</mapper>
mapper interface:
#Mapper
public interface ConfigurationMapper {
String containsKey(#Param("configKey") String configKey);
}

Answer 1

Found it. The answer is in the XMLConfigBuilder:
Environment environment = configuration.getEnvironment();
if (environment != null && databaseIdProvider != null) {
String databaseId = databaseIdProvider.getDatabaseId(environment.getDataSource());
configuration.setDatabaseId(databaseId);
}
The environment must be configured in order to make the databaseId work.
Here is how to use multi-db support in spring environment: http://www.mybatis.org/spring/factorybean.html
<bean id="vendorProperties" class="org.springframework.beans.factory.config.PropertiesFactoryBean">
<property name="properties">
<props>
<prop key="SQL Server">sqlserver</prop>
<prop key="DB2">db2</prop>
<prop key="Oracle">oracle</prop>
<prop key="MySQL">mysql</prop>
</props>
</property>
</bean>
<bean id="databaseIdProvider" class="org.apache.ibatis.mapping.VendorDatabaseIdProvider">
<property name="properties" ref="vendorProperties"/>
</bean>
<bean id="sqlSessionFactory" class="org.mybatis.spring.SqlSessionFactoryBean">
<property name="dataSource" ref="dataSource" />
<property name="mapperLocations" value="classpath*:sample/config/mappers/**/*.xml" />
<property name="databaseIdProvider" ref="databaseIdProvider"/>
</bean>