Objectify: Unable to evaluate the expression Method threw 'com.googlecode.objectify.LoadException' exception

Question

i am learning how to store and retrieve data with the google app engine and objectify, and set up a test project in intellij-idea. i created a simple entity that looks like this:

ContactType

@Entity
public class ContactType {

@Id
public Long id;
public String name;

    public ContactType(String name){
        this.name = name;
    }
}

before i start testing i delete all saved instances i created before in my servlet:

deleting old data

Objectify ofy = ObjectifyService.ofy();
ObjectifyService.register(ContactType.class);

List<Key<ContactType>> contactTypes = ofy.load().type(ContactType.class).keys().list();
    ofy.delete().keys(contactTypes).now();

after that i save this entity like this:

saving new data

ContactType contactType1 = new ContactType("contactType1");
ContactType contactType2 = new ContactType("contactType2");
ofy.save().entity(contactType1 ).now();
ofy.save().entity(contactType2 ).now();

then i retrieve the objects i just saved like this:

retrieving data

 List<ContactType> list= ofy
                .load()
                .type(ContactType.class)
                .list();

and get the 2 expected objects. but when i comment out the lines that delete and save the old entries, and just want to retrieve the entries that i saved last time (and which i can still see in the development console), and inspect the returned entries with the intellij-idea debugger, i just get this small error message and no stacktrace in the console at all.:

debugging error message

Unable to evaluate the expression Method threw 'com.googlecode.objectify.LoadException' exception.

and when i change the "view as" option from "list" to "toString" in the intellij-idea debugger i get only following information:

so my questions are:

how can i save and retrieve data with objectify?
how can i see a detailed error stacktrace when something goes wrong?

richard richard · Accepted Answer · 2016-09-04T10:26:16

i finally fixed this problem. when i try to get the size of the returned list and put a try/catch around it then i get an error message that my entity does not have a default constructor without parameters.

    try{
        List<ContactType> list= ofy
            .load()
            .type(ContactType.class)
            .list();  
        int size = list.size();
    }catch(LoadException e){
        String message = e.getMessage();
    }

after adding following construtor everything works fine:

public ContactType(){
    name = "";
}

Objectify: Unable to evaluate the expression Method threw 'com.googlecode.objectify.LoadException' exception

2 Answers