So I have the follow entity with the following code to create and update the object. The resulting data after calling the method is that the field Value has the value of 1 in the Datastore running at my local computer. Why? Isn't the object JPA-managed (or attached as described in this article) and supposed to update itself upon em2.close()?
Entity:
#Entity
public class MyObj {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
public Long Id;
public int Value = 0;
}
Code:
public void createAndUpdate() {
Long id = null;
// Line below calls Persistence.createEntityManagerFactory("transactions-optional").createEntityManager()
EntityManager em1 = Database.getEntityManager();
MyObj obj = new MyObj();
obj.Value = 1;
em1.persist(obj);
em1.close();
id = obj.Id;
EntityManager em2 = Database.getEntityManager();
obj = (MyObj) em2.find(MyObj.class, id);
obj.Value = 2;
// NOTE1
em2.close();
}
On the line marked NOTE1 I have tried inserting em2.persist(obj) and em2.merge(obj) (even though from what I've read, that should not be neccessary since find() returns an attached object). None of them helped.
I'm using JPA v1.
As the JPA spec says, you cannot directly update fields of Entity objects, yet in your posted code you do just that (so the persistence provider has no way of knowing that something has changed, and so can't flush those changes to the datastore).
DataNucleus JPA does actually allow you to update the field directly if you enhance the class that does it to be "PersistenceAware".
Solution : use setters to update fields
Related
I want to save both child and parent entities whenever a POST call is made. I have an Item entity with a one to one mapping to a parent table Attribute:
#Entity
#Table(name="Item")
#JsonIgnoreProperties(ignoreUnknown = true)
public class Item
{
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name="id")
private Long id;
#OneToOne(fetch=FetchType.LAZY)
#JoinColumn(name="attr_id")
private Attribute attribute;
#OneToMany(mappedBy = "item", cascade = CascadeType.ALL, orphanRemoval=true)
private List<ValueSet> valueSets = new ArrayList<>();
// Other fields, getters, setters, overriding equals and hashcode using Objects.equals() and Objects.hashCode() for all the fields, helper for adding and removing ValueSet
}
The Attribute entity looks like this:
#Entity
#Table(name="Attribute")
#JsonIgnoreProperties(ignoreUnknown = true)
public class Attribute
{
#Id
#Column(name="id")
private Long id;
// Other fields, getters, setters, NOT overriding equals hashCode
}
Whenever an Item gets saved I need the Attribute to get saved as well. I've my postman sending JSON POST data as follows:
{
"attribute":{
"id":"6"
},
"valueSets":[
{
"value":"basic"
}
]
}
My handler looks like this:
#PostMapping("/item")
public void postItems(#RequestBody Item item)
{
itemRepository.save(item);
}
ItemRepository is just a one liner with #Repository annotation:
public interface ItemRepository extends CrudRepository<Item, Long>
When I try to save the Item I run into - Cannot insert the value NULL into column 'attr_id', table 'Item'; column does not allow nulls. INSERT fails.
I can't figure out why is it unable to take the id value of 6 that I am supplying as part of my POST invocation. The id value 6 already exists on the Attribute table. I have also tried making the relationship bi-directional using mappedBy and CASCADE.ALL but still get the same error.
Any thoughts/suggestions on what I'm messing/missing? Also, is there a better approach to handle nested entities? Should I try to save each of them individually? In that case can the #RequestBody still be the parent entity?
I have built an example project, and try to replicate your situation, not successful. I am able to insert the "item" without any issue.
I placed the project under this repository https://github.com/hepoiko/user-5483731-1
Hope this help you to troubleshooting further or let me know If I miss anything in there.
I am using Objectify to store data on Google App Engine's datastore. I have been trying to implement a one-to-many relationship between two classes, but by storing a list of parameterised keys. The method below works perfectly some of the time, but returns an empty array other times - does anyone know why this may be?
It will either return the correct list of CourseYears, or
{
"items": [
]
}
Here is the method:
#ApiMethod(name = "getCourseYears") #ApiResourceProperty(ignored = AnnotationBoolean.TRUE)
public ArrayList<CourseYear> getCourseYears(#Named("name") String name){
Course course = ofy().load().type(Course.class).filter("name", name).first().now();
System.out.println(course.getName());
ArrayList<CourseYear> courseYears = new ArrayList<CourseYear>();
for(Key<CourseYear> courseYearKey: course.getCourseYears()){
courseYears.add(ofy().load().type(CourseYear.class).id(courseYearKey.getId()).now());
}
return courseYears;
}
The Course class which stores many CourseYear keys
#Entity
public class Course {
#Id
#Index
private Long courseId;
private String code;
#Index
private String name;
#ApiResourceProperty(ignored = AnnotationBoolean.TRUE)
public List<Key<CourseYear>> getCourseYears() {
return courseYears;
}
#ApiResourceProperty(ignored = AnnotationBoolean.TRUE)
public void setCourseYears(List<Key<CourseYear>> courseYears) {
this.courseYears = courseYears;
}
#ApiResourceProperty(ignored = AnnotationBoolean.TRUE)
public void addCourseYear(Key<CourseYear> courseYearRef){
courseYears.add(courseYearRef);
}
#Load
#ApiResourceProperty(ignored = AnnotationBoolean.TRUE)
List<Key<CourseYear>> courseYears = new ArrayList<Key<CourseYear>>();
...
}
I am debugging this on the debug server using the API explorer. I have found that it will generally work at the start for a few times but if I leave and return to the API and try and run it again, it will not start working again after that.
Does anyone have any idea what might be going wrong?
Many thanks.
You might want to reduce the amount of queries you send to the datastore. Try something like this:
Course course = ofy().load().type(Course.class).filter("name", name).first().now();
ArrayList<CourseYear> courseYears = new ArrayList<CourseYear>();
List<Long> courseIds = new List<>();
for(Key<CourseYear> courseYearKey: course.getCourseYears()){
courseIds.add(courseYearKey.getId());
}
Map<Long, Course> courses = ofy().load().type(CourseYear.class).ids(courseIds).list();
// add all courses from map to you courseYears list
I also strongly recommend a change in your data structure / entities:
In your CourseYears add a property Ref<Course> courseRef with the parent Course and make it indexed (#Index). Then query by
ofy().load().type(CourseYear.class).filter("courseRef", yourCourseRef).list();
This way you'll only require a single query.
The two most likely candidates are:
Eventual consistency behavior of the high replication datastore. Queries (ie your filter() operation) always run a little behind because indexes propagate through GAE asynchronously. See the GAE docs.
You haven't installed the ObjectifyFilter. Read the setup guide. Recent versions of Objectify throws an error if you haven't installed it, so if you're on the latest version, this isn't it.
I have two tables: Word and Adjective, both with some properties. Primary key of both tables is ID, Adjective.ID also references Word.ID as foreign key so there is a 1-1 relationship.
I also have a repository for any kind of table with an Update function.
public void Update(T entity) {
var entry = DatabaseContext.Entry(entity);
DatabaseSet.Attach(entity);
entry.State = EntityState.Modified;
}
I take a value from the database, convert it into a ViewModel looking like this (of course it's actually a little more complex):
public class WordModel {
public int ID { get; set; }
public string OriginalWord { get; set; }
}
public class AdjectiveModel : WordModel {
public string Translation { get; set; }
}
Then I alter the values of properties Word and Translation, convert and write it back. After conversion I have an object like this:
Word = {
ID = 1
OriginalWord = y
Adjective = {
ID = 1
Translation = z
}
}
Upon updating however, only one table gets updated.
Database.Words.Update(Word) only updates the OriginalWord value in the Word table,
Database.Adjectives.Update(Word.Adjective) only updates the Translation value in the Adjective table.
When running the updates for both tables sequentially I get an InvalidOperationException: An object with the same key already exists in the ObjectStateManager. The ObjectStateManager cannot track multiple objects with the same key.
Creating a new database entry works perfectly.
I cannot believe I have to update both tables on their own and then save the context for each. I have created the database Repository via a Tutorial that obviously didn't explain well enough what's going on with the DbSet and the DbContext, which leaves me a little helpless here.
Sadly I have no link (it is quite a while ago I created the database project)
So, what am I doing wrong here?
You entity Word contains an entity Adjective, it is then the root of the object graph. Now generally here's what you should keep in mind in the following situations :
All objects in the graph are new (new word and new adjective)
use myDbContext.Words.Add(myNewWordObjectGraph); to have the correct state you want.
Only root is new (new word and a pre-existing non modified adjective)
use myDbContext.Entry(myNewWord).state = EntityState.Added; to have the correct state you want.
Root is modified and some nodes are modified (word and adjective both exist in the DB and both have been modified)
use myDbContext.Entry(myWord).State = EntityState.Modified; and myDbContext.Entry(myAdjective).State = EntityState.Modified; to have the correct state you want. i.e. call myDbContext.Entry(myObject).State = EntityState.Modified; for each modified object in the graph whether it's the root or some other node.
Root is unchanged and/or Modified and some nodes are added, others are also unchanged and/or modified
use myDbContext.MyRootObjectDbSet.Add(myRootObject); ; this will mark all the objects in the graph as EntityState.Added including the unchanged and/or modified objects. so the next call should be for each unchanged and/or modified object in order to correct its state : myDbContext.Entry(myObject).State = ThisObjectSCorrectState;.
I Hope that helps
EDIT
Calling DbSet.Attach(...) just adds the object to the objects tracked by EF. If you modify an object before calling DbSet.Attach(...), the modifications won't be persisted to DB when you call SaveChages(), so attaching an object as is before modification, calling DbSet.Attach(...) and then modifying the object is the way to make EF aware of the modifications.
Based on the way your update method's defined I would assume your repository looks something like this maybe?
//Not threadsafe as it contains a transient object 'DbContext'.
public class Repository<T> : IRespository<T> where T : class
{
private readonly MyDbContext context;
public Repository(MtDbContext context)
{
this.context = context
}
//...
public void Update(T entity) {... }
public void Commit() { context.SaveChanges(); }
}
I would suggest changing the update method to the following :
public void Update(T entity)
{
context.Entry(entity).State = EntityState.Modified;
}
And this update method would be called for each object you updated in the graph using the same instance of the repository enclosing the DbContext.
I'm currently developing a mobile application who uses a Google App Engine-hosted web service.
But i'm facing an issue. I just want to add a field in one my database's table.
App Engine doesn't use classic SQL syntax, but GQL. So i cannot use the ALTER TABLE statement. How can i do this with GQL ? I looked for a solution on the web, but there's not a lot of help.
public MyEntity() {
}
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private Key idStation;
private String name;
private double longitude;
private double latitude;
private java.util.Date dateRefresh = new Date(); //the field i want to add in DB
So, now when i create a "MyEntity" object, it should add the "dateRefresh" field into the database... I create my object like this:
MyEntity station = new MyEntity();
station.setName("test");
station.setLatitude(0);
station.setLongitude(0);
station.setDateRefresh(new Date("01/01/1980"));
DaoFactory.getStationDao().addStation(station);
addStation method:
#Override
public MyEntity addStation(MyEntity station) {
EntityManager em = PersistenceManager.getEntityManagerFactory().createEntityManager();
try {
em.getTransaction().begin();
em.persist(station);
em.getTransaction().commit();
} finally {
if(em.getTransaction().isActive()) em.getTransaction().rollback();
em.close();
}
return station;
}
The field "dateRefresh" is never created into my DB...
Someone to help me please ?
Thanks in advance
Just add another field to your data structure, maybe providing a default clause, and that's all. For example, if you have a UserAccount:
class UserAccount(db.Model):
user = db.UserProperty()
user_id = db.StringProperty()
you may easily add:
class UserAccount(db.Model):
user = db.UserProperty()
user_id = db.StringProperty()
extra_info = db.IntegerProperty(default=0)
timezone = db.StringProperty(default="UTC")
and let it go.
While the datastore kinda mimics tables, data is stored on a per entity basis. There is no schema or table.
All you need to do is update your model class, and new entities will be saved with the structure (fields) of the new entity.
Old entities and indexes, however, are not automatically updated. They still have the same fields as they had when they were originally written to the datastore.
There's two ways to do this. One is to make sure your code can handle situations where your new properties are missing, ie make sure no exceptions are thrown, or handle the exceptions properly when you're missing the properties.
The second way is to write a little function (usu a mapreduce function) to update every entity with appropriate or null values for your new properties.
Note that indexes are not updated unless the entity is written. So if you add a new indexed property, old entities won't show up when you query for the new property. In this case, you must use the second method and update all the entities in the datastore so that they are indexed.
I have an entity in my app engine datastore. There's actually only one instance of this entity. I can see it in my admin console. Is it possible to add a new attribute to the entity via the admin console (using gql perhaps)?
Right now it looks something like:
Entity: Foo
Attributes: mName, mAge, mScore
and I'd like to add a new boolean attribute to this entity like "mGraduated" or something like that.
In the worst case I can write some code to delete the entity then save a new one, but yeah was just wondering.
Thanks
-------- Update ---------
Tried adding the new attribute to my class (using java) and upon loading from the datastore I get the following:
java.lang.NullPointerException:
Datastore entity with kind Foo and key Foo(\"Foo\") has a null property named mGraduated.
This property is mapped to com.me.types.Foo.mGraduated, which cannot accept null values.
This is what my entity class looks like, I just added the new attribute (mGraduated), then deployed, then tried loading the single entity from the datastore (which produced the above exception):
#PersistenceCapable
public class Foo
{
#PrimaryKey
private String k;
/** Some old attributes, look like the following. */
#Persistent
#Extension(vendorName = "datanucleus", key = "gae.unindexed", value="true")
private String mName;
...
/** Tried adding the new one. */
#Persistent
#Extension(vendorName = "datanucleus", key = "gae.unindexed", value="true")
private boolean mGraduated;
The only way to implement this is to use Boolean as the type for the new property..
Than in set method you can accept boolean value, that's no issue.
If you want the get method to also return boolean.. you also can, but be sure to check if the value is null and if so.. return default value (e.g. true)
so
private Boolean newProp = null; // can also assing default value .. e.g. true;
public void setNewProp(boolean val)
{
this.newProp = val;
}
public boolean getNewProp()
{
if(this.newProp == null)
return true; // Default value if not set
return this.newProp.booleanValue();
}
I recommend you not to migrate your data in this case - it can be very costly and can deplete your quota easily (read old data, create new, delete old = 3 operations for every entry in you data store)
You can't do this through the admin console, but you shouldn't have to delete the entity. Instead just update it- the Datastore does not enforce schemas for Kinds.
E.g., if Foo is a subclass of db.Model (Python), change your model subclass to include the new property; fetch the model instance (e.g., by its key), update the instance, including setting the value of the new field; and save the modified instance. Since you just have one instance this is easy. With many such instances to update you'd probably want to do this via task queue tasks or via a mapreduce job.
You have declared the new mGraduated field using the primitive type boolean, which cannot be null. The existing entity can't be loaded into the model class because it doesn't have this property. One option is to declare this property using the Boolean class, which can accept a null value.
The Admin Console only knows about properties in existing entities. You cannot use the Admin Console directly to create a new property with a name not used by any existing entities. (This is just a limitation of the Console. App code can do this easily.)