Question

I’m trying to have a conditional query fragment, based upon a parameter which comes from the mybatis configuration, rather than a query parameter. Something like this:

<sql id="frag">
    <if test="col_name != null">
        SELECT * FROM TABLE WHERE ${col.name}=#{value}
    </if>
    <if test="col_name == null">
        SELECT * FROM TABLE WHERE SAMPLECOL=#{value}
    </if>
</sql>

where the value of col_name is a global parameter, specified inside the .properties file read by the mybatis configuration.

Apparently this does not work; looking at the source code, it seems that the OGNL expression evaluator is not aware of the configuration properties (which instead are working when I have the parameter substitution, through ${...} inside the SQL). Did anybody find a way to do this?

Answer 1

I found out this is not currently possible; the OGNL has effectively no access to configuration properties.

As a workaround, as suggested in this post on the mybatis mailing list, I wrote a simple interceptor which reads configuration parameters and adds them to the query parameter map. Not exactly clean, but it works.

Interceptor code:

@Intercepts({
    @Signature(type = Executor.class,
    method = "query",
    args = {MappedStatement.class, Object.class, RowBounds.class, ResultHandler.class})})
public class ConfigPropInterceptor implements Interceptor {

    private final Map<String, Object> properties = new HashMap<String, Object>();

    @Override
    public Object intercept(Invocation invocation) throws Throwable {
        Object param = invocation.getArgs()[1];
        if (param instanceof Map) {
            ((Map<String, Object>)param).putAll(properties);
        }
        return invocation.proceed();
    }

    @Override
    public Object plugin(Object target) {
        return Plugin.wrap(target, this);
    }

    @Override
    public void setProperties(Properties properties) {
        for (String p : properties.stringPropertyNames()) {
            this.properties.put(p, properties.getProperty(p));
        }
    }
}

Example usage in configuration .xml:

<plugins>
    <plugin interceptor="...ConfigPropInterceptor">
        <property name="_issuerLocation" value="${issuer.location}"/>
    </plugin>
</plugins>

With this setting, I was able to test the _issuerLocation variable in OGNL expressions like everything else.