I know how to use this function as a black box, aka, what goes in, what comes out, but I cannot figure out how the heck this function actually works.

In short, .eq() takes in 3 parameters, a condition, a functional interface, and a value. If the condition is true, the function generates a SQL string similiar to where column_name = value. However, I am trying to figure out how it infers the column name from the functional interface.

This is where the function is used,

public class MyImpl extends ServiceImpl<MyEntityDao, MyEntity> implements MyService {

    // function in question
    public MyEntity select(MyEntity condition) {
        LambdaQueryWrapper<MyEntity> wrapper = Wrappers.lambdaQuery();
        wrapper.eq(Objects.nonNull(condition.getId()), MyEntity::getId, condition.getId());
        ...
    }
}

where

public interface MySerivce extends IService<MyEntity> { }

First of all, getId() is a simple getter/setter of the form public int getId() { return this.id; }. How would a static method MyEntity::getId be allowed when I have only defined getters/setters for instances. In fact, a simple check Arrays.asList(1, 2, 3).forEach(MyEntity::getId); gives the compile error Non-static method cannot be referenced from a static context. Apparently, JAVA complains that I am using a non-existant static class method. So, why is there no warning when I used it on the provided .eq() method?

Similarly, when digging throught the source code, MyBatis tries to parse the functional interface as a string,

protected String columnToString(SFunction<T, ?> column) {...}

this is where I am starting to suspect that MyBatis was generating some methods without my knowledge. It somehow transforms the supplier myinstance.getId() into a function Y <- MyEntity.getId(X). But again, I cannot find a way to test my hypothesis, or I could be completely wrong from the get go.

Anyway, looking for some insights. Thanks beforehand.