I am working on a EJB/JPA project.
I have two tables:
BusinessOwner and Clients.
Each of these tables has a super class, Person.
I have a table that keeps all their transactions, both BusinessOwner and Clients.
In the Transaction table, I have a field UserID, that points to the primary key of both BusinessOwners and Clients, as a foreign key.
How do i map these as in my entity class.
You should be able to have a OneToMany from Person to Transaction and a ManyToOne from Transaction to Person, but this depends on how you have mapped inheritance?
Related
I am using Spring data JPA(Hibernate).
I am trying to join my tables (Table A & Table B) but on Non-Primary Columns. Is it possible to actually do that? I am trying to use referenceColumnName, but it seems to not working, giving error :
Cannot set int to Integer.
When I am removing referenceColumnName, then it is working but obviously it is joining with Primary Key. Also in case of One-to-one Bidirectional, where should I place mappedBy & JoinColumn?
The annotation #JoinColumn indicates that this entity is the owner of the relationship (that is: the corresponding table has a column with a foreign key to the referenced table), whereas the attribute mappedBy indicates that the entity in this side is the inverse of the relationship, and the owner resides in the "other" entity.
Regarding the other question of using joining tables on Non-Primary columns, there are plenty of threads why don't you go through. for example
Does the JPA specification allow references to non-primary key columns?
Is there a way to map multiple foreign keys to the same navigation property of an entity? I have a table with a self-referencing many to many relationship defined by a relationship table.
For example, I have a Person table and I want to define the different related people. I created another table, PersonRelationship, that defines those relationships with 2 foreign keys to the Person table. It doesn't matter if the person is referenced in the first or the second foreign key just that the person is in one. I would like my Person entity to have a list of all the relationships but instead it has two lists of relationships: one in which the person is in the first foreign key and another where it is the second foreign key.
How can I map these two foreign keys so that they map to the same list in the Person entity? (I am using a database first approach)
how to implement Foreign key relation in JPA side ( There is no foreign key for this relation in db, Db owned by another application , i cant able to change db structure( SW vendor not allowing me to do it)
Is there just no foreign key constraint, or nothing referencing the id at all?
If there is just no constraint, then it does not matter, JPA does not care if there is a constraint or not, just use the column that references the id.
If there is nothing referencing the id, then you cannot have a relationship with nothing store it. If you cannot alter the table, then perhaps you can add a new table that defines the join between the two tables (similar to a many to many, but JPA also allows a join table to be used for a one to one).
I'm new to Entity Framework and just experimenting...
Consider 3 db tables where Person is a base table. I want the Employe table to enherit from Person, storing employee specific info. It seems that EF requires that PersonId also be the PK of the Employee table, so I made EmployeeID a unique index.
Next I added a table, Application, which stores one record for every software application that the Employee supports, creating a foreign key from Application.EmployeeId to Employee.EmployeeId.
However, EF doesn't seem to recognize relationships that involve unique indexes, but only Primary Keys.
What I can do is create a relationship from Application.PersonId to Person.PersonId, however, only Employees can be responsible for an Application, so it seems more natural to me to have Application as a "child" of the Employee table rather than the Person table.
Is this possible in EF?
You can build your relation between Employee (PersonId) and Application (EmployeeId). In such case the integrity should work as you expect because only PersonIds in Employee table will be only for existing employees. EF has currently no support for unique keys.
Is it possible to create associates b/t 2 non-key fields in the Entity Framework?
Example: Take the 2 tables in a legacy application (i.e. keys/structure cannot change)
Order (
OrderId : int : PK
OrderNo : varchar
)
OrderDetails (
DetailRecordId : int : PK
OrderNo : varchar
)
In the Entity Framework, I want to create an association b/t Order and OrderDetails by the OrderNo field, which is not a primary key on either table or a FK relationship in the database.
This seems to me as not only should it be easy to do, but one reasons to use something like EF. However, it seems to only want to allow me to create associations using entity keys.
The Entity Framework allows you to claim that columns are keys and that FK constraints exist where none actually exist in the database.
That is because the SSDL (StorageModel part of the EDMX) can if necessary be manipulated by you and lie about the database.
The EF will then interact with the database as if the keys and foreign keys really do exist.
This should work, but all the normal caveats about referential integrity apply.
See my Entity Framework Tips
Hope this helps.
The problem with using non-key fields to define relationships is that the keys are not guaranteed to be properly navigatable. That could lead to a situation where you have a one to one relationship between two entities where there are more than one possible rows that fufill the relationship.
...when relating data from a database, the relationships should always be based on keys. The keys enforce the referential integrity.
One more workaround:
create view vOrder which will not include PK and create Entity from it.
Set PK in this entity to OrderNo
Now you will be able create association