I'm trying to annotate my JPA-Entity. In the entity I want to map another Entity which should be loaded by values of the root entity.
Example:
Entity A has the fields key1 & key2.
I want to map Entity B which should be loaded by the filter b.key1 = a.key1 & b2.key2 = a.key2
Can anyone help?
I got the solution. I just used #ManyToOne and #JoinColumns:
#ManyToOne
#JoinColumns(
{
#JoinColumn(name="key1", referencedColumnName="refKey1"),
#JoinColumn(name="key2", referencedColumnName="refKey2")
}
)
private EntityB entityB;
Related
I have a table Person and now I want to express a relation like "best friend". Assuming a person can only have one best friend I don't want to alter the Person table to add a best friend column, rather I want to have an additional mapping table, e.g.:
Table Person (id name):
1 foo
2 bar
3 somebody
4 somebodyelse
Table BestFriendMapping (personId bestfriendId):
1 2
3 4
I was doing something like this:
class Person {
#OneToOne()
#Fetch(FetchMode.SELECT)
#JoinTable(name = "BestFriendMapping",
joinColumns = #JoinColumn(name = "personId", referencedColumnName = "id"),
inverseJoinColumns = #JoinColumn(name = "bestfriendId",
referencedColumnName = "id"))
private Person bestFriend;
}
The problem is, that now when I add a new Person, the mapping table is populated with two entries, for example the newly added Person is having id=10 and his bestFriend 20, then the entries are:
10 20
20 10
I would like to have just one entry, but still be able to get the best friend of a person no matter which I have in my hand currently. I found out that I probably have done two unidirectional instead of one bi-directional mapping, so I have to use mappedBy, but I am not sure what is the syntax when it is about the one and the same entity object, thus one and the same field inside the object. The examples on the internet are always showing the mapping of two entities via a mapping table.
Or maybe something like this?!? In addition to the JoinColumns and InverseJoinColumns to add mappedBy to the OnetoOne just like this #OneToOne(mappedBy="bestFriend"), kind of weird :)
I annotated my fields with only #OneToOne and when I check the database (generated using liquibase) saw that there are unique constraints on database columns.
Does this mean #OneToOne implies uniqueness just by itself, eg. one Building can only be in one city, and no other Buildings can be in the same city?
What do I do when I want to tell that there may be other other buildings in the same city?
add #JoinColumn(unique = false),
only use #JoinColumn(unique = false) without #oneToOne,
or use #ManyToOne?
or leave it without any annotations?
I don't want to put a Buildings field in the city class, because I wouldn't ever call city.getBuildings();. Does any of the below require a bidirectional reference?
class Building {
#OneToOne(optional = false)
City city;
}
class Building {
#OneToOne(optional = false)
#JoinColumn(unique = false)
City city;
}
class Building {
#JoinColumn(unique = true)
City city;
}
class Building {
#ManyToOne
City city;
}
The JPA specification says that for a bidirectional OneToOne relationship (2.10.1 Bidirectional OneToOne Relationships):
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 has the same type as the primary key of table B and there is a unique key constraint on it.
In case of unidirectional OneToOne relationship (2.10.3.1 Unidirectional OneToOne Relationships):
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 has the same type as the primary key of table B and there is a unique key constraint on it.
If you have a City-Building relationship, then for any reasonable city it would be a OneToMany/ManyToOne relationship, since a given city can have multiple buildings, but a given building can be only in one city.
I've two entities, let's call them entityA and entityB, entityA has a not nullable attribute entityBID. In my form for entityA creation I'd like to add a select with some entityB names ( not id ) that I would select in a function ( which would be in Repository/entityBRepository if possible ).
Thanks :)
I'm not sure of what you're asking, but i guess you are making a choice (or entity) field type of entityB class.
Those kind of field use the __toString() function of entity class (or getId() by default).
So just add in your entityB class
public function __toString()
{
return $this->getName();
}
Maybe this is a question with an easy answer ... but I don't get it running. At persist() I get the exception that the referential key in the child table is null (which of course is not allowed by the database). I have a recipe and some steps for preparation.
I'm using EclipseLink 2.4.1
Recipe.java (rcpid is autoset by JPA)
#Entity
public class Recipe {
#Id
long rcpid;
List<Recipestep> recipesteps = new ArrayList<>();
#OneToMany(
cascade=CascadeType.ALL,
fetch=FetchType.EAGER,
mappedBy="recipe",
targetEntity=Recipestep.class )
// This does NOT work. Following line tries to access a join-table !!!
// #JoinColumn(name="rcpid", referencedColumnName="rcpid")
public List<Recipestep> getRecipesteps() { return recipesteps; }
// some more attributes, getters and setters
}
Recipestep.java (rpsid is autoset by JPA)
#Entity
public class Recipestep {
#Id
long rpsid;
Recipe recipe;
#ManyToOne( targetEntity=Recipe.class )
#JoinColumn( name="rcpid" )
public Recipe getRecipe() { return recipe; }
// some more attributes, getters and setters
}
The code above is a valid workaround. However to have clean (and supportable) code, the relationship should be only one-way with a collection in the parent which references all its children.
You have mapped this as a unidirectional one to many, but have two mappings for the recipestep rcpid database column. Try changing the long rcpid to
#ManyTOne
Recipe rcp;
And then remove the joincolumn definition from the oneToMany and make it bidirectional by marking it as mappedby the rcp manyToOne relation. An example is posted here http://wiki.eclipse.org/EclipseLink/UserGuide/JPA/Basic_JPA_Development/Mapping/Relationship_Mappings/Collection_Mappings/OneToMany
Eclipselink will always insert nulls on unidirectional oneToMany relations using a joincolumn when first inserting the target entity, and then update it later when it processes the Recipe entity. Your rcpid mapping in Recipestep is also likely null, which means you have two write able mappings for the same field which is bad especially when they conflict like this.
You are experiencing the default JPA behaviour. Adding an entity to the recipesteps list is not sufficient to create a bidirectional relation.
To solve the issue you need to set the rcpid explicitly on every element in the list.
EDIT: I think the issue is that JPA does not know where to store the id of the Recipe in the Recipestep table. It assumes a name ("recipebo_rcpid"), but your table seems to lack it.
Try adding the column "recipe_id" to the Recipestep table and a mappedBy attribute to the #OneToMany annotation:
#OneToMany(
cascade=CascadeType.ALL,
fetch = FetchType.EAGER,
mappedBy = "recipe" )
You probably do not need the targetEntity attribute in the annotation- the List is typed already.
I am trying to map an Address entity and a Person entity using a OneToMany mapping: "Each person has only one address but an Address can have many people".
#RooJavaBean
#RooToString
#RooEntity(identifierColumn = "addressID")
public class Address {
#OneToMany(cascade = CascadeType.ALL, **mappedBy = "address**")
private Set<Person> persons = new HashSet<Person>();
}
I cannot figure out what to map the Address entity with (bold), i have very little experience with JPA(Eclipse Link) and Spring roo but i thought the mappedBy should equal addressID and for a bidirectional ManyToOne on my Person entity mappedBy should equal personID?
As any JPA docs would tell you (all JPA implementations provide them), mappedBy is the name of the field of type "Address" in Person class. If you don't have a field of that type in Person, then the relation is not bidirectional and so you don't use "mappedBy"