When creating an #Entity mapping a table my IDE notifies me: Persistent entity '*******' should have primary key.
But the table in the DB doesn't have an ID (I think it's bad but it's legacy which I've no permissions to fix)
What should I do? Will it work if I just omit the ID field? Or should I make up an ID which is not mapped on the table but satisfy the code?
Every JPA entity must have a primary key.
You can find the documentation here.
From the Java Persistence book: Identity and Sequencing: here
If your object does not have an id, but its table does, this is fine.
Make the object an Embeddable object, embeddable objects do not have
ids. You will need a Entity that contains this Embeddable to persist
and query it.
Try also to read the answers here
Related
I am not familiar with Hibernate. I am trying to understand the purpose of defining a primary key class in Hibernate and where it would be appropriate.
I have to add new classes to some old code (early versions of Hibernate). I have a table called LOG which has the following fields among other fields
ID NUMBER
TRANS_ID VARCHAR2(40)
ID is the primary key (populated by oracle sequence). TRANS_ID is unique and populated by the application. Only search needed is by the TRANS_ID. There are no composite keys.
I believe I will need to define an entity class called Log.java and DAO class called LogDAO.java but do I need to define a LogPK.java for the Id field? I would not like to define one if this is not needed in my situation.
I am using hibernate and i mapped my table with my bean. If i am not assign any particular column value as #id, it throws "No identifier specified for entity" error, however it is not primary key in my data table. I want to add multiple records with same data. how can i do it? When i annotated my product Name column with #id my code runs perfect.
Hibernate requires an identifier for each entity. However, it is possible to use native queries to insert new records. And, in the same way, to recover them.
I have a data model in which a number of entities inherit some common attributes from a single superclass entity. I am using InheritanceType.JOINED on the superclass, which causes Hibernate to create a single table for attributes defined in the superclass, with subclass tables containing only columns that are added by the subclass (so to load the attributes for a subclass instance, a join is performed between the two tables). That is all working fine.
What I'd like to do, however, is specify a unique constraint that includes fields in both the subclass and superclass tables. For instance, say that my superclass entity is something like:
Thing: {id, name}
...and then I have some subclass entities like:
Company: {address} //inherits 'id' and 'name' from 'Thing'
Employee: {company} //inherits 'id' and 'name' from 'Thing'
...and I want to configure Hibernate to automatically enforce that a given Company cannot have two Employee's with the same name. The company field is in the Employee table, but the name field is in the Thing table, so is there any way to get Hibernate to enforce this constraint, or do I need to do it programmatically whenever I add a new Employee?
If it's not possible in the Database it won't be possible with Hibernate. You can't create one constraint on multiple tables with SQL so neither in Hibernate.
You could work around this by creating a new Entity holding only the company and employee id and setting a unique constraint on those 2 fields but I would recommend enforcing this programmatically.
You could not use InheritanceType.JOINED, then everything ends up in a huge table, and you could write your constraint. As said before: What you want is just not possible in a relational DB.
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.
I have a MySQL table without primary key, and I have to map it into a JPA entity. I cannot modify the table in any way.
Because entities must have a primary key, I have to specify one. If I'm certain that the field I use as a primary key in the entity (or the fields, should I opt for using composite primary key) will always be unique (and not null) in table, can the fact that the table doesn't have a primary key specified in CREATE TABLE cause any issues?
That's correct. JPA has no way of knowing if the column(s) it is using as a PK is actually a real PK in the database. If those column(s) are, in practice, a PK, then it should be fine.
You may potentially get some performance problems if the pseudo-PK columns are not correctly indexed, though - JPA will execute queries against the PK on the assumption that it will perform well.
JPA itself doesn't analyze your database. Just don't use common methods using primary key (find/merge/...) instead use named queries, for example using jpql update syntax.
#Entity
#Table(name = "login")
#NamedQueries({
#NamedQuery(name = "Login.updateLastOnline",
query = "UPDATE Login l SET l.lastOnline = :newDate WHERE l.loginId = :loginId")
})
public class Login implements Serializable
{
It doesn't matter if loginId is primary key