Add sql comment with distributed tracing id globally on mybatis - mybatis

Question

Is there a cool way to add sql comment like below on Mybatis.
SELECT * FROM users; /* TraceID: foo-bar-baz */
I would like to add sql comment with TraceID/RequestID/CorrelationID in the context of distributed tracing to all executed sql.
This comment enables to identify a transaction from the comment of a slow query.
I found Interceptor API, but I seem that cannot add commnet.
I seem that we can use scripting like thymeleaf-scripting in this way.
But, We need to add sql comment in all sql...
Any advice will be appreciated.

Answer 1

In your case, a custom language driver might be a good fit.
Implementation
The below implementation is mostly the same as the default XMLLanguageDriver.
import org.apache.ibatis.builder.xml.XMLMapperEntityResolver;
import org.apache.ibatis.mapping.SqlSource;
import org.apache.ibatis.parsing.PropertyParser;
import org.apache.ibatis.parsing.XNode;
import org.apache.ibatis.parsing.XPathParser;
import org.apache.ibatis.scripting.defaults.RawSqlSource;
import org.apache.ibatis.scripting.xmltags.DynamicSqlSource;
import org.apache.ibatis.scripting.xmltags.TextSqlNode;
import org.apache.ibatis.scripting.xmltags.XMLLanguageDriver;
import org.apache.ibatis.session.Configuration;
public class CommentLanguageDriver extends XMLLanguageDriver {
#Override
public SqlSource createSqlSource(Configuration configuration,
XNode script, Class<?> parameterType) {
// Append comment
script.getNode().setTextContent(
script.getNode().getTextContent() + getComment());
return super.createSqlSource(configuration, script,
parameterType);
}
#Override
public SqlSource createSqlSource(Configuration configuration,
String script, Class<?> parameterType) {
if (script.startsWith("<script>")) {
XPathParser parser = new XPathParser(script, false,
configuration.getVariables(), new XMLMapperEntityResolver());
return createSqlSource(configuration,
parser.evalNode("/script"), parameterType);
} else {
// Append comment
script = PropertyParser.parse(script + getComment(),
configuration.getVariables());
TextSqlNode textSqlNode = new TextSqlNode(script);
if (textSqlNode.isDynamic()) {
return new DynamicSqlSource(configuration, textSqlNode);
} else {
return new RawSqlSource(configuration, script, parameterType);
}
}
}
private String getComment() {
// OGNL expression invoking the static method
return " /* ${#org.slf4j.MDC#get(\"requestid\")} */";
}
}
The appended comment contains an OGNL expression invoking the static method.
This expression is evaluated at runtime.
Configuration
To register the custom language driver globally, you need to set defaultScriptingLanguage in the config.
<settings>
<setting name="defaultScriptingLanguage"
value="pkg.CommentLanguageDriver" />
</settings>
If you are using mybatis-spring-boot-starter, add the following line to your application.properties.
default-scripting-language-driver=pkg.CommentLanguageDriver