CODEWITHSUNDEEP
google-app-engineobjectify
MPKenning
MPKenning

Reputation: 569

Why does this get method stop returning correctly?

I am trying to write an app engine application for my university. What I am trying to achieve right now, is to create a method which takes in a Course name, and returns a list of all the CourseYears (think of that as being like a link table e.g. if Maths is the course, and it has Year 1, year 2 and Year 3; MathsYear1, MathsYear2 and MathsYear3 would be the names of the CourseYears).

This is the code for the module (WARING: super dirty code below!):

    @ApiMethod(name = "courseYears") 
public ArrayList<CourseYear> courseYears(@Named("name") String name){
    DatastoreService datastore = DatastoreServiceFactory.getDatastoreService();

    Query.Filter keyFilter = new Query.FilterPredicate("name", Query.FilterOperator.EQUAL, name);

    Query query = new Query("Course").setFilter(keyFilter);
    PreparedQuery preparedQuery = datastore.prepare(query);

    List<Entity> resultList = preparedQuery.asList(FetchOptions.Builder.withLimit(1));

    Course course = ofy().load().type(Course.class).id(resultList.get(0).getKey().getId()).now();

    ArrayList<String> courseYearNames = course.getAllCourseYearNames();

    System.out.println(course.getName());

    ArrayList<CourseYear> courseYears = new ArrayList<CourseYear>();

    for(String courseYearName: courseYearNames){
        Query.Filter courseNameFilter = new Query.FilterPredicate("name", Query.FilterOperator.EQUAL, courseYearName);
        Query query2 = new Query("CourseYear").setFilter(courseNameFilter);
        List<Entity> resL = preparedQuery.asList(FetchOptions.Builder.withLimit(1));

        System.out.println("test");

        CourseYear courseYear = ofy().load().type(CourseYear.class).id(resL.get(0).getKey().getId()).now();
        courseYears.add(courseYear);
    }

    return courseYears;
}

It basically takes a Course name in, applies a filter on all courses to get the corresponding Course object, and then calls getAllCourseYearNames() on the course to get an array list containing all its CourseYears' names. (I would have loved to do this using Keys, but parameterised Objectify keys don't seem to be supported in this version of App Engine).

I then try and get the CourseYears by looping through the arraylist of names and applying the filter for each name. I print "test" each time to see how many times it is looping. Like I said, a super dirty way of doing it.

When I try passing a few course names as a parameters, it loops the correct number of times only once or twice, and after that does not loop at all (doesn't print "test"). I could understand if it never looped, but not doing it correctly once or twice and then never again. It doesn't successfully return a list of CourseYears when it does work, but rather the relevant number of NULLs - I don't know if this is relevant. I believe it successfully retrieves the course every time, as I print the name of the course after loading and it never fails to do this.

If anyone has ANY suggestions for why this may be happening, I would be incredibly grateful to hear them!

Thanks

Upvotes: 0

Views: 35

Answers (1)

Andrei Volgin
Andrei Volgin

Reputation: 41089

query2 is never used in your code. You reuse preparedQuery from your previous query, which runs on a different entity kind.

Upvotes: 2

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