In JPA project, when I generate tables for entities I can't see any table foreign key constraints created on database side.
I concluded that JPA cannot create table foreign key constraints in database and that referential integrity is enforced in JPA (on application side) and not by database.
Can someone confirm if this is so?
According to the JPA 2.2 specification, the persistence manager should create foreign key constraints. For example in the case of a one-to-one mapping:
Assuming that:
Entity A references a single instance of Entity B.
Entity B references a single instance of Entity A.
Entity A is specified as the owner of the relationship.
The following mapping defaults apply:
Entity A is mapped to a table named A.
Entity B is mapped to a table named B.
Table A contains a foreign key to table B. The foreign key column name is formed as the concatenation of the following: the name of the relationship property or field of entity A; the name of the primary key column in table B. The foreign key column has the same type as the primary key of table B and there is a unique key constraint on it.
Related
The entity A has an OneToMany relation with the entity B. I would like to use a composite primary key for the entity B, where one of the columns is the same as the the primary key of the entity A and the second column should be generated. How can the second column be started from 1 whenever the the other involving column within the composite primary key changes?
I use Oracle data bank and could not find any solution.
Thanks in advance!
I'm trying to understand On Delete and On Update foreign key functions in Entity Framework.
I have a database first (sqlite) model consisting of two tables:
Control
ID
Name
ControlTypeID
and
ControlType
ID
Name
The foreign key constraints on ControlTypeID are set to "On Delete Set Default" and "On Update Cascade." Default is set to "1" on ControlTypeID
The tables are bound to a datagridview. When I delete a ControlType (say, ID=2) rather than Control.ControlTypeID being set to 1, it is set to null.
Does entity framework not preserve the database foreign key constraint rules when it constructs the entity model?
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?
I have a database that has a table with a 2-column primary composite key (one int, one bigint.) I have two tables that have a composite foreign key, referencing the first table's composite primary key. The relationships are (as far as I know,) fine and dandy on the database itself.
When generating a DB context via DB-first EF6, these relationships/navigation properties are not represented in the generated models (No virtual members in the two child tables referencing the parent table.)
Since it's db-first, I can't modify the models.
In this case you can put those relationships into the onmodelcreating function in db context. We can put constraint there.
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).