I have 3 tables working as LetterOfCredit has many ProformatInvoice which has many PurchaseOrder.
I would like to get in my entity LetterOfCredit the list of all the PurchaseOrder linked via ProformatInvoice.
In SQL it looks like :
SELECT *
FROM purchase_order
JOIN proformat_invoice pi ON pi.id = pi_id
JOIN letter_of_credit lc ON lc.id = pi.lc_id
WHERE lc_id = 3;
But in LetterOfCredit.java, I tried to use proformat_invoice as a jointable but I get an empty list....
#OneToMany(fetch = FetchType.LAZY)
#JoinTable(
name="proformat_invoice",
joinColumns = #JoinColumn(name="lc_id", referencedColumnName = "id"),
inverseJoinColumns = #JoinColumn(name="id", referencedColumnName = "pi_id")
)
private List<PurchaseOrder> purchaseOrders;
Could you tell me what I did wrong?
We can fetch the grand children efficiently by using hibernate annotation ---- #OneToMany( mappedBy = "category", fetch = FetchType.LAZY ).
So in this case this will not give an exception if its unable to fetch the sub children till session is open.
We can manually pull the sub children by using the getters in our code without getting any exception , as we have already told the compiler that it will be lazy loading because there are child elements and there sub child elements.
Related
I have 2 entities with oneToMany relationship. I want to maintain the insertion order for child entity. I used #orderColumn for that. Code:
Parent Class:
#Entity
public class Order{
private String orderId;
#OneToMany(mappedBy = "order", cascade = CascadeType.ALL, fetch = FetchType.LAZY, orphanRemoval = true)
#NotEmpty
#OrderColumn
private List<OrderItem> orderItems = new ArrayList<>();
}
Child class:
#Entity
public class OrderItem{
#Id
private String orderItemId;
#ManyToOne
#JoinColumn(name = "order_id", nullable = false)
private Order order;
}
The issue that I'm facing here is orderColumn is not backward compatible. i.e. it adds an column in the child table with name "order_item_order". It works fine for the records that are getting created after this change but for the previous records, the column is null and it results in below exception:
org.hibernate.HibernateException: null index column for collection
I have tried setting the default value to 0 for the column. In that case it returns only one record for child.
Suggestions please.
You have two solutions :
Proceed with the #OrderColumn but fill it with the right values : index starting at 0, incrementing by 1 (migrate your data thanks to a sql scripts or a two steps migration from java)
Proceed with #OrderBy annotation : add a creation_date column, fill it when you store the object (like in the create(ModelClass model) method of your repository) and set it to a default value in the past
Hello how can I put "unassigned" value on a table that has a join with cascade on delete with an other table instead of leaving it in null in an entity?
#OneToMany(fetch = FetchType.LAZY,cascade= CascadeType.ALL)
#JoinColumn(name = "departmentName")
I have the following hibernate entity:
#Entity
public class Customer {
#OneToMany(mappedBy = "customer", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private List<Address> addresses = new ArrayList<>();
#OneToMany(mappedBy = "customer", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private List<Contact> contacts = new ArrayList<>();
#OneToMany(mappedBy = "customer", cascade = CascadeType.ALL, fetch = FetchType.EAGER)
private List<Name> names = new ArrayList<>();
// Many more, including a primary key
}
Starting the application, I got the following exception:
org.hibernate.loader.MultipleBagFetchException: cannot simultaneously fetch multiple bags
If I remove one arbitary OneToMany association, or if I add a #Fetch(value = FetchMode.JOIN) to an arbitary OneToMany association, everything works fine.
Is this a hibernate bug, a hibernate limitation, or is there anything wrong with my entity? TIA!
It is not a bug. It is because of Hibernate uses a one select with a join to fetch all the data. Hibernate can join three and more tables, but the result of joining will have duplicates of, for example, Address columns. Hibernate needs to remove duplicates — it is a reason why Set works.
Possible workarounds:
Use Set<Address> instead of List<Address>. You should use Set for all collections.
Use lazy fetching fetch = FetchType.LAZY
Use #Fetch(value = FetchMode.SUBSELECT)
Some additional reading:
A beginner’s guide to Hibernate Set and List behavior
Hibernate does not return distinct results for a query with outer join fetching enabled for a collection (even if I use the distinct keyword)?
Try to use:
#OneToMany
#LazyCollection(value=LazyCollectionOption.TRUE)
private Collection<Name> names = new ArrayList<>();
When I persist a list which has an order, the result in the database has a different order. How can I persist a many-to-many relationship with list order in JPA?
#Entity
#Table(name = "house")
public final class House {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long id;
#Basic(optional = false)
#Column(name = "name")
private String name
#ManyToMany(cascade = CascadeType.ALL)
#JoinTable(name = "house_room",
joinColumns =
#JoinColumn(name = "id_house", referencedColumnName = "id"),
inverseJoinColumns =
#JoinColumn(name = "id_room", referencedColumnName = "id"))
private List<Room> rooms;
}
House object:
Room room1 = new Room();
room1.setName("Kitchen");
Room room2 = new Room();
room2.setName("Bathroom");
Room room3 = new Room();
room3.setName("Bedroom");
List<Run> runs = new ArrayList<Run>();
rooms.add(0,room2);
rooms.add(1,room1);
rooms.add(2,room3);
House cottage = new House();
cottage.setRooms(rooms);
persist(cottage); // order in database should be "room2", "room1" then "room3" but it is saved as "room1", "room2" then "room3"
There are 2 ways to order list in JPA using #OrderBy and #OrderColumn annotations. #OrderColumn is perhaps what you are looking for.
#OrderBy
Specify an ordering rule based on the comparison of a particular attribute of the entity or element
Example:
#OrderBy("name ASC")
private List<Room> rooms;
By adding an #OrderBy annotation on the mapping, we can indicate that we want the rooms to be ordered in ascending alphabetical order by its name attribute.
Note: We needn’t have included the ASC in the #OrderBy annotations because it would be ascending by default.
Simply changing the order of the items in a List in memory will not cause that order to be stored in the database at commit time.
The annotation applies only when collection is retrieved from the database. That means, the order will not be stored in the database but when data is retrieved from the DB and stored to the List collection in memory, they will be ordered.
#OrderColumn
The OrderColumn annotation specifies a column that is used to maintain the persistent order of a list. Example:
#OrderColumn(name="ROOM_ORDER")
private List<Room> rooms;
This means you have an additional column named "ROOM_ORDER" that will indicate the order of your items in your table.
Relational databases do not store order of referenced data. In order to store the order of elements in a list, JPA needs another column in DB table. You may map the column with #OrderColumn in the same ways, as you mapped #JoinColumn (you just need single #OrderColumn, even when you used multiple #JoinColumn annotations)
I jave the following mapped superclass that provides a basic implementation for a parent/child self relationship to create a parent/child list for unlimited nesting of items (i.e. Categories)
#MappedSuperclass
public abstract class ParentChildPathEntity<N extends ParentChild> implements MaterializedPath<N> {
#ManyToOne(fetch=FetchType.LAZY)
#JoinColumn(name = "parent_id")
private N parent;
#Column(name = "name", unique = true)
private String name;
#OneToMany(mappedBy = "parent", fetch = FetchType.LAZY, cascade = CascadeType.ALL)
private Set<N> children = new HashSet<N>();
If I load the entire table with fetch join on the parent and children, a single select loads all the records and i can happily traverse the tree. my problem comes in when i specify to retrieve a node on the tree. i want the node and all its children in a single select. below is the hql for loading the entire table:
hql.append(String.format("tree from %s tree ", tableName));
hql.append("left join fetch tree.parent ");
hql.append("left join fetch tree.children ");
if i specify the node name, i.e.:
where tree.name = :name
then hibernate retrieves the node, but when i access the children i get the SELECT N+1 issue. I realize why this is happening, (because of the tree.name = :name) but is there a way to write the HQL so it loads the specified node and all its children?
I'm just trying to figure out a way to support a simple nested item's list where i can retrieve any parent node and its children with a single select
thanks in advance,
Have you tried using the #BatchSize annotation?
#BatchSize(size = 20)
Ex:
#OneToMany(mappedBy = ..., fetch = FetchType.LAZY)
#BatchSize(size = 20)
public SortedSet<Item> getItems() { ... }
Then, if you specify the join to children in your HQL, you should be able to avoid n+1 select. I am not sure, offhand, if there is a way to specify the batch size in the HQL statement.