Dynamically select mapped class constructor in `SimplePropertyRowMapper`

[hansdesmet]

When I have a class with multiple constructors:

class Person {
  private int id;
  private String name;
  Person(int id, String name) {
    this.id = id;
    this.name = name;
  }
  Person(String name) {
    this(0, name);
  }
}

I can't use it as a parameter of the method query of JdbcClient:

jdbcClient.sql("select id,name from persons").query(Person.class).list();

It causes an exception:

java.lang.IllegalStateException: No primary or single unique constructor found

This is a pity: when i make a new Person somewhere in my code, i can't type:

new Person("John");

but I must type (id is an autonumber in the database):

new Person(0, "John"); // a surrogate value for id

Is it possible to relax this one-constructor restriction a bit?

• If JdbcClient detects multiple constructors, it counts the number of columns in the ResultSet of the query.
• If there is only one constructor with the same number of parameters as this number of columns, it uses that constructor.

[sbrannen]

FYI: The reason for the current behavior is that SimplePropertyRowMapper eagerly resolves the mappedConstructor and caches it.

Thus, the proposal here is effectively for SimplePropertyRowMapper.mapRow(ResultSet, int) to dynamically choose an appropriate constructor for the current ResultSet.

[hansdesmet]

Perhaps you can cache multiple constructors in a Map where the key of the map is the number of constructor parameters.