Getting Column Names Or Table Dynamically in MyBatis

Most of the time, you know exactly the column names of a database table you are retrieving the data from. But there might be times when you just want to display the table dynamically without knowing the column names beforehand, for instance when you need to write an admin module.

If you use normal JDBC, you normally use the ResultSetMetaData object to achieve that and you can get all the column names from there. But how are you gonna do it in MyBatis? There are some other more complicated ways to do it but this is the simplest and the most straight forward.

The solution is to use resultType instead of resultMap in MyBatis mapping config as the following.

<select resultType="java.util.LinkedHashMap" id="getTableData " parameterType="String">
        ${queryString}
</select>

We use java.util.LinkedHashMap for resultType. You can also use normal HashMap but you might not wanna use that because HashMap doesn't maintain the insertion order. That's about it for the configuration. You do not need to configure the mapper for the resultType like resultMap because MyBatis automatically populates the results in LinkedHashMap for you.

So let's suppose, this is the MyBatis DAO interface.

public interface Xyz {
     public List<Map> getTableData(Query query);
}

Note the return type. It must be a List. MyBatis returns a list of Map objects. One Map object represents one row of data.
In a Map object, the "key" is column name and the value is the value of that column in the respective row.

This is it. Call the method and now you've got all the column names and values.
If you need column names, you can just call keySet() from the Map object and you will get all the column names in a Set.

Just iterate through the List, iterate through each Map object inside, print it out and experiment with it. You will know what you have to do next.