Some Background
I have a game database with a table called Games that has multiple attributes and one called Genres. The Genres attribute is defined as an integer[] in PostgreSQL. For the sake of simplicity, I'm not using any foreign key constraints, but essentially each integer in this array is a foreign key constraint on the id attribute in the Genres table. First time working with the NetBeans Master/Detail Sample Form and Java persistence and it's been working great so far except for 1 thing. I get this error when the program tries to display a column that has a 1-dimensional integer array. In this example, the value is {1, 11}.
Exception Description: The object [{1,11}], of class [class org.postgresql.jdbc3.Jdbc3Array], from mapping [oracle.toplink.essentials.mappings.DirectToFieldMapping[genres-->final.public.games.genres]] with descriptor [RelationalDescriptor(finalproject.Games --> [DatabaseTable(final.public.games)])], could not be converted to [class [B].
Exception [TOPLINK-3002] (Oracle TopLink Essentials - 2.0.1 (Build b09d-fcs (12/06/2007))): oracle.toplink.essentials.exceptions.ConversionException
My Research
From what I've been able to read, it looks like PostgreSQL arrays need something special done to them before you can display and edit them in this template. By default, the sample form uses TopLink Essentials (JPA 1.0) as its persistence library, but I can also use Hibernate (JPA 1.0).
Here is the code that needs to be changed in some way. From the Games.java file:
#Entity
#Table(name = "games", catalog = "final", schema = "public")
#NamedQueries({
// omitting named queries
#NamedQuery(name = "Games.findByGenres", query = "SELECT g FROM Games g WHERE g.genres = :genres")
})
public class Games implements Serializable {
#Transient
private PropertyChangeSupport changeSupport = new PropertyChangeSupport(this);
private static final long serialVersionUID = 1L;
// omitting other attributes
#Column(name = "genres")
private Serializable genres;
// omitting constructors and other getters/setters
public Serializable getGenres() {
return genres;
}
public void setGenres(Serializable genres) {
Serializable oldGenres = this.genres;
this.genres = genres;
changeSupport.firePropertyChange("genres", oldGenres, genres);
}
} // end class Games
Here are also some of the sites that might have the solution that I'm just not understanding:
https://forum.hibernate.org/viewtopic.php?t=946973
http://blog.xebia.com/2009/11/09/understanding-and-writing-hibernate-user-types/
// omitted hyperlink due to user restriction
Attempted Solutions
I'm able to get the data to display if I change the type of genres to String, but it is immutable and I cannot edit it. This is what I changed to do this:
#Column(name = "genres")
private String genres;
public String getGenres() {
return genres;
}
public void setGenres(String genres) {
String oldGenres = this.genres;
this.genres = genres;
changeSupport.firePropertyChange("genres", oldGenres, genres);
}
I also attempted to create a UserType file for use with Hibernate (JPA 1.0), but had no idea what was going wrong there.
I also attempted to use the #OneToMany and other tags, but these aren't working probably because I'm not using them properly.
What I'm Looking For
There has to be a simple way to get this data to display and make it editable, but since I'm completely new to persistence, I have no idea what to do.
The effort put into your question shows. Unfortunately JPA does not currently support PostgreSQL arrays. The fundamental problem is that arrays are not frequently used in many other databases frequently and so heavy reliance on them is somewhat PostgreSQL specific. Thus you can expect that general cross-db persistence API's are not generally going to support them well if at all. JPA is no exception, having currently no support for PostgreSQL arrays.
I have been looking at writing my own persistence API in Java that would support arrays, but it hasn't happened yet, would be PostgreSQL-only when written, and would be based on a very different principle than JPA and friends.
Related
I have a table which contains a column of type: integer[]
I'm trying to map my entity to this table and I've tried the following suggestion of:
#ElementCollection
private ArrayList<Integer> col;
public MyEntity() {
col = new ArrayList<>();
}
However I get the following error: Illegal attempt to map a non collection as a #OneToMany, #ManyToMany or #CollectionOfElements
Not sure how to get around this. I'm open to changing the entity's datatype, but I would prefer not to move this property into its own table/entity. Is there another solution? Thanks.
The field must be of type List<Integer>, not ArrayList<Integer>.
The JPA engine must be able to use its own List implementation, used for lazy-loading, dirty checking, etc.
It's a good idea in general to program on interfaces rather than implementations, and it's a requirement to do it in JPA entities.
I've a legacy database that all sites have, it describes specific content in a number of catagory/subcatagory/child item format. Until now, adding/editing the content is either manual work in the tables OR raw sql Windows Forms tool (I built when I started out in the job!).
I would like Entity Framework style drag, drop, bind and run coding ability with WPF 4.5 and .net 4.5.
I hesitate to use NHibernate as EF5 is very simple to get going with, I understand Nhibernate is more work (albeit a faster ORM). Are there alternatives that work well? I'm trying to avoid too much manual setup, if possible. The editor isn't a mandatory project and I can't justify lots of extra work on it - but it would make my job easier for the next 2 years if a nice version of it was put together.
All the argument against Access I know really well :) - swapping this isn't an option for at least a year.
Having searched the StackOverflow site, I don't see too many questions asking for this, but apologies if I've missed a good one!
Update: I think I should refine my question slightly as really what I needed to get at what code generation so that I don't need to hand build all the classes for the Access database. From what I can see, Dapper's work is around efficiency but is distinct from generating code. Coming from a entity framework mindset, I can see where I've conjoined the tasks somewhat in my thinking :). So apart from boil my own - does anyone know a good code gen for use with Access. This I can marry to Dapper :).
You can't use Entity Framework, because it doesn't work with Access databases.
It's possible to use NHibernate with MS Access, although NH doesn't support Access out of the box.
You need NHibernate.JetDriver from NHContrib and here are example settings for the NH config file.
If I recall it correctly, NH Contrib needs to be compiled against the exact NH version you're using, so you probably need to download the source code and compile it by yourself.
As an alternative, you can use one of the many micro-ORMs, for example Stack Overflow's own Dapper.
Dapper is DB agnostic, so it can connect to everything including Access. Quote from the official site:
Will dapper work with my db provider?
Dapper has no DB specific implementation details, it works across all .net ado providers
including sqlite, sqlce, firebird, oracle, MySQL and SQL Server
The disadvantage is that because Dapper is DB agnostic, you have to implement some advanved stuff yourself, like paging.
EDIT:
IMO Dapper is in the "fairly easy to run quickly catagory".
Take a look at this:
(complete demo project here)
using System;
using System.Data.OleDb;
using Dapper;
namespace DapperExample
{
class Program
{
static void Main(string[] args)
{
using (var con = new OleDbConnection("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=test.mdb"))
{
var list = con.Query<Product>("select * from products");
Console.WriteLine("map to a strongly typed list:");
foreach (var item in list)
{
Console.WriteLine(item.ProductNumber + " : " + item.Description);
}
Console.WriteLine();
var list2 = con.Query("select * from products");
Console.WriteLine("map to a list of dynamic objects:");
foreach (var item in list2)
{
Console.WriteLine(item.ProductNumber + " : " + item.Description);
}
Console.ReadLine();
}
}
}
public class Product
{
public string ProductNumber { get; set; }
public string Description { get; set; }
}
}
There are two different queries in this example code.
The first one maps to a strongly typed list, e.g. the result is an IEnumerable<Product>. Of course it needs a Product class that it can map to.
The second query returns an IEnumerable<Dynamic> (>= .NET 4.0) which means that the properties are evaluated on the fly and you don't need to define a class before, but the disadvantage is that you lose type safety (and IntelliSense).
My personal opinion is that the missing type safety is a deal breaker for me (I prefer the first query syntax), but maybe this is something for you.
Hate to resurrect an old thread but I recently did a WPF project using PetaPoco, a micro-ORM, with MS Access so I thought I'd share my implementation.
To add MS Access support to PetaPoco, you just need to add a couple of bits of code:
First add an AccessDatabaseType class. All of the DataBaseType classes are at the end of the PetaPoco.cs file. Just add the new class after SqlServerDatabaseType.
class AccessDatabaseType : DatabaseType
{
public override object ExecuteInsert(Database db, IDbCommand cmd, string PrimaryKeyName)
{
db.ExecuteNonQueryHelper(cmd);
return db.ExecuteScalar<object>("SELECT ###IDENTITY AS NewID;");
}
}
Next, modify PetaPoco.Internal.DatabaseType.Resolve() to support the AccessDatabaseType. (This code assumes you are using the Jet OLEDB provider)
public static DatabaseType Resolve(string TypeName, string ProviderName)
{
//...
if (ProviderName.IndexOf("Oledb", StringComparison.InvariantCultureIgnoreCase) >= 0)
return Singleton<AccessDatabaseType>.Instance;
// Assume SQL Server
return Singleton<SqlServerDatabaseType>.Instance;
}
Finally, to instantiate PetaPoco use this:
Db = New PetaPoco.Database("Provider=Microsoft.Jet.OLEDB.4.0;Data Source=C:\db.mdb", "System.Data.Oledb")
Limitations:
PetaPoco assumes your primary keys are autonumber/identity fields. If you have a PK that's not an autonumber or you have a composite PK, you'll need to implement your own insert & save logic.
I didn't need paging in my application so I didn't implement it.
We are using
Jet Entity Framework Provider. That way we can easily port to another database later.
It does not have all the limitations mentioned above and works great.
Tortuga Chain fully supports Access.
https://docevaad.github.io/Chain/Introduction.htm
I am using Objectify to manage GAE Datastore for my GWT app. The problem is that I am not using queries properly and I get UmbrellaExceptions as per below:
Caused by: java.lang.RuntimeException: Server Error: java.lang.String cannot be cast to java.lang.Number
at com.google.web.bindery.requestfactory.shared.Receiver.onFailure(Receiver.java:44)
Say that I have a class Box with a unique field String id. I want to get the Box object whose id == "cHVQP6zZiUjM"
This is how I do it now:
public Box getBox(String boxId)
{
Objectify ofy = ObjectifyService.begin();
Query<Box> q=ofy.query(Box.class).filter("id",boxId);
Box targetBox = q.get();
return targetBox;
}
#Entity
public class Box extends DatastoreObject{
private String id;
private String title;
}
I tried doing this with ofy.load() but that method is not defined in my class Objectify (I don't know why).
Your key is encoded. Try using:
Box targetBox = ofy.get(Box.class, KeyFactory.stringToKey(boxId));
To decode your key.
The short answer: You are missing the #Id annotation in your entity.
The long answer: Id fields are special in the datastore. The id is not a real property, but rather a part of the Key that identifies the entity. You can't really filter on id fields, but you can filter on a special field called __key__. Objectify is somewhat clever about letting you filter by the id field and converting this to a __key__ filter under the covers, but it can't do it if you don't annotate the entity properly!
Actually I'm a little confused because Objectify shouldn't let you register the entity without an #Id field.
By the way, there are two sections of the documentation: Objectify4 (release coming soon) and Objectify3. Since you're using Ofy3, there is no load() method.
Another thing: Get-by-key operations are strongly preferred to queries when the operations are equivalent (as they are in your example).
This is my first question on any of these websites so pardon my unprofessionalism.
I use playframework with SIENA module (with GAE) and I came accross the following problem:
Given 3 entities:
public class Meeting extends Model{
#Id
public Long id;
public String place;
#Owned
Many<MeetingUser> users;
.
.
.
}
public class User extends Model{
#Id
public Long id;
public String firstName;
public String lastName;
#Owned
Many<MeetingUser> meetings;
.
.
.
}
public class MeetingUser extends Model{
#Id
public Long id;
public Meeting meeting;
public User user;
.
.
.
public User getUser(){
return Model.all(User.class).filter("id", user).get();
}
public Meeting getMeeting(){
return Model.all(Meeting.class).filter("id", meeting).get();
}
}
For instance I am listing a meeting and all their users:
public static void meetingInfo(Long meetingId){
Meeting meeting = Models.all(Meeting.class).filter("id",meetingId);
List<MeetingUser> meetingusers = meeting.asList();
List<User> users = new ArrayList<User>();
for(MeetingUser mu: meetingusers){
users.add(mu.getUser());
}
render(users);
}
This is done(is there any better way here?) however when it comes to filtering (especially dynamic filtering for many many fields) I can not use the Query's filter method on the MeetingUser as I need to filter on a MeetingUser's field's field (firstName). The same problem arise for ordering. I need the solution for both problems.
I hope my problem is clear and I appreciate any kind of help here.
Remember that you are in GAE which is a NoSQL DB.
So you can't do Join request as in RDBMS.
Yet, this is not really the pb you have so this was just to be sure you are aware of it ;)
So if you want to find the person having given firstname in a given meeting, can you try the following:
List<MeetingUser> meetingusers = meeting.users.asQuery().filter("firstname", "XXX");
(you can also order)
Nevertheless, knowing that you can't join, remember that you can't write a query searching for a meeting in which there are users whose firstname is XXX as it would require some joins and it doesn't exist in GAE. In this case, you need to change your model following NoSQL philosophy but this is another subject
regards
Let's try to give a way to do what you want...
Your relation is a Many-to-Many which is always the worst case :)
You want to filter Meeting by User's firstname.
It requires a join request which is not possible in GAE. In this case, you must change your model by denormalizing it (sometimes use redundancy also) and manage the join by yourself. Actually, you must do the job of the RDBMS by yourself. It seems overkill but in fact, it's quite easy. The only drawback is that you must perform several requests to the DB. NoSQL means No Schema (& No Join) so there are a few drawbacks but it allows to scale and to manage huge data load... it depends on your needs :)
The choice you did to create the MeetingUser which is a "joined" table and a kind of denormalization is good in GAE because it allows to manage the join yourself.
Solution:
// fetch users by firstname
List<User> users = users.all().filter("firstName", "John").fetch();
// fetch meetingusers associated to these users (verify the "IN" operator works because I didn't use that for a long time and don't remember if it works with this syntax)
List<MeetingUser> meetingusers = MeetingUser.all().filter("user IN", users);
// now you must fetch the whole meeting because in MeetingUser, only the Meeting ID is stored (other fields are Null or O)
List<Meeting> meetings = new ArrayList<Meeting>()
for(MeetingUsers mu:meetingusers) {
meetings.add(meetingusers.meeting);
}
// use the batch feature to fetch all objects
Meeting.batch(Meeting.class).get(meetings);
// you have your meetings
Hope this helps!
I'm pretty new to JPA/JDO and the whole objectdb world.
I have an entity with a set of strings, looks a bit like:
#Entity
public class Foo{
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
private Key id;
private Set<String> bars;
public void setBars(Set<String> newBars){
if(this.bars == null)
this.bars = new HashSet<String>;
this.bars = newBars;
}
public Set<String> getBars(){
return this.bars;
}
public void addBar(String bar){
if(this.bars == null)
this.bars = new HashSet<String>;
this.bars.add(bar);
}
}
Now, in another part of the code, I'm trying to do something like this:
EntityManager em = EMF.get().createEntityManager();
Foo myFoo = em.find(Foo.class, fooKey);
em.getTransaction().begin();
myFoo.addBar(newBar);
em.merge(myFoo);
em.getTransaction().commit();
When, of course, newBar is a String.
But, what I get is:
javax.jdo.JDODetachedFieldAccessException: You have just attempted to access field "bars" yet this field was not detached when you detached the object. Either dont access this field, or detach it when detaching the object.
I've searched for an answer, but I couldn't find one.
I've seen someone ask about a Set of strings, and he was told to add an #ElementCollection notation.
I tried that, but I got an error about the String class Metadata (I don't really understand what it means.)
I would really appreciate some help on this thing, even a good reference to someone explaining this (in simple English).
OK,
So I found the answer in some blog.
So for anyone who's interested:
In order to use a Collection of simple data types (in JPA), a
#Basic
notation should be added to the collection. So from my example at the top, It should've been written:
#Basic
private Set<String> bars;
So you are using JPA, right? (I see EntityManager rather than JDO's PersistenceManager.) Since you are getting a JDO error, I suspect that your app isn't configured properly for JPA.
JPA docs: http://code.google.com/appengine/docs/java/datastore/jpa/overview.html
JDO docs: http://code.google.com/appengine/docs/java/datastore/jdo/overview.html
You need to pick one datastore wrapper and stick with it. The default new app with the Eclipse tools is configured for JDO, and it is a reasonable choice, but you'll have to change your annotations around a little bit.