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How to Pass Specific Pair from Hibernate Many-to-Many Relationship

I am setting up a Many-to-Many relationship similar to the example here: https://dzone.com/tutorials/java/hibernate/hibernate-example/hibernate-mapping-many-to-many-using-annotations-1.html.
If I want to create another entity called Grade that contains a specific Student-Course pair, how can I do that? I know I can have Grade reference Student and Course individually, but that doesn't reference the STUDENT_COURSE table. Ideally I would be able to have a StudentCourse object in my Grade class, but I don't know how to do that without creating a StudentCourse entity myself.

Hibernate Mapping

I have an issue in performing Hibernate Mapping. The scenario is as follows:
There is a User class which has username, name, dateofbirth, image and other information pertaining to a user with username as the primary key.
Second class is Product class which has product id and other information related to a product with primary key as product key.
The third class is Order class which has OrderId, OrderDate, Username- should be foriegn key-referring to the User class username and finally a Set of type Product- because one order can have many products.
Now I want the primary key of the Order class as a composite key (OrderId, ProductID) and this productID should be reference from Product Class.
The relationships that I want to create are as follows:
1. One order can belong to only one User
2. One order can have many products
Can someone lead me on how to go about it? Any kind of help will be great.

I think most likely you are thinking similar relationship. Difference in your requirement is you need One to Many mapping from Order/PurchaseOrder to Product/Item and you don't want Shipment.
My suggestion would be:
Create bi-directional one-to-many relationship b/w User and Order. Benefit for bidirectional is you can access User Object from Order Object, if not required, you can keep it unidirectional from User to Order.
Create one-to-many relationship b/w Order and Product.
Instead of composite key in order, keep the primary key as just OrderID. You can still fetch list of products from your order object and order object from user object.
The whole point in making this decision is from which object you derive remaining objects. With ORMs you should know from which object you would derive rest and so my suggestion is based on assumption that you will have User object available as attached entity, so you can get list of orders (defined as set) and from a particular order find out list/set of Products.
In case you have Order object available first, then create a bidirectional with User. So that you can find list/set of Products at one end, and Customer associated at other.
For ORM mappings refer Hibernate Mapping Examples.
Hope this clarifies.

Is it common to have for the fields in a form to have its own class?

sample:
I have 2 tables, department and employees (these 2 table is link via the department_id foreign key in employees). and obviously, department has a one-to-many relationship with the employees table.
I need to create a form that has a subset of data from both tables.
These are fields in the web form.
family/surname (from employees table)
first name (from employees table)
employment start date (from employees table)
department (drop-down list of the various departments with department_id as the value return and obviously from the departments table).
I'm wondering if creating a new class for these 4 fields is "best practice"? Thanks! :)

If you are just returning one of each, you can simply add them to the Model. If you are returning a bunch of "rows" of these things, then I would say it makes more sense to wrap the values in a Bean and pass back a collection of instances of that bean. It makes it easier to look through them on the view-side.

access data from table in many to many relationship in hibernate

I have three table's student , course , student_course
table student
{
student_id(PK)
}
table course
{
course_id(PK)
}
table student_course
{
student_id(PK+FK)
course_id(PK+FK)
}
I created model class's and configuration files using Hibernate Generation Tool.
It create following files-
1) student.java & student.hbm.xml
2) course.java & course.hbm.xml
And for student_course it creates set in each hbm file with Many-to-Many relationship.
So I want Course object's related to student, for this i want to access student_course table separately.
Right Now i access Course object related to student by accessing set of student_course through student object.I think it is not efficient one.
What is the efficient way to this?
Can i do this
by writing sql query or
by manually creating studentCourse.java & studentCourse.hbm.xml
please suggest me efficient way to access course object's related to student object.

please suggest me efficient way to access course object's related to
student object.
I think what you've got it the right approach. There is a link table but Hibernate has hidden it through the use of a ManyToMany - this is the correct modelling for this relationship. A student can take many courses and a course has many students.

JPA to retrieve name-value from child table without using model for child

This is something I'd really like to be able to do - resolve names based on id values without fetching the whole child model.
Here is an example of what I have, a Table say Employee and a Name_Details table
The Employee may look like this
Create Table Employee {
emp_idinteger not null generated by default as identity; -- generated pk
Department varchar(44);
emp_name_id Integer; -- fk to Name_Details table
...other details such as hire_date etc..
}
now emp_id is a foreign key to the name_details table which may look like this:-
Create Table Name_Details {
id Integer;
Name varchar(32);
Address Varchar(127);
Postcode Varchar(10);
--other details..
}
My question is that I'd like to model the first table Employee with a Java class but I am not interested in setting up a one-to-one relationship between the Employee class and the Name_Details table to fetch that whole Name_details table (as its quite large) the only information I want from this second class is just the Name field (found by joining the emp_name_id column with the Name_Details.id column.
So is it possible in JPA to say declare something like a transient variable in my Employee class called say String employeeName and have this retrieved by JPA based on the above relationShip?
This is a simplified example of what I have wgere there are several tables with name-value pairs and the master table has the values. I need this for reading and not updating/deleting etc.
I am not using JPA v1.x with EJB3 (and not hibernate) on WPS 6.1
Thx G

There are a few options.
The first is to just create a Name class that maps to Name_Details but only maps the name and id fields. Employee would then have a OneToOne to Name, and only the name would be read.
A second option is define Name_Details as a #SecondaryTable in Employee and map only the name from it. The JPA spec restricts the secondary table join to have to share the same id, but depending on what JPA provider you are using, using the 1-1 foreign key may be possible (EclipseLink does support this). You could also define a view the does the join and map to the view.
A third solution is to still map all of the Name_Details fields but define them as LAZY. If your JPA provider supports LAZY basics (or fetch groups), then these will not be fetch unless accessed.