I'm using MS SQL Server + Hibernate (JPA, more precisely, with EntityManager) and i faced with the problem: I need to store entity into appropriate table in my DB; this table has uniqueidentifier as primary key; and storing entity already has UUID (it's primary key), with witch it should be inserted into the DB.
Problem is that when i try to merge my entity, hibernate do some magic and store my entity with another UUID value. So, when I fetch this entity from db and take a look on it ID, I see inappropriate value.
So, I want to tell hibernate not to do that (or, maybe, there is another solution?).
My entity class:
public class Entity extends BaseEntity {
#Id
#GeneratedValue(generator = "uuid2")
#GenericGenerator(name = "uuid2", strategy = "uuid2")
#Column(name = "id_column")
private UUID uuId;
// other fields, getters, setters
}
Also, I have one more 'annoyance': my IDE and my DB browser shows me another ID in that column. I mean, when I stop my app in the debug mode and look at the id of an entity, I see different value from a value in the database.
Thanks in advance!
Related
Method to store entity:
PoolDef poolDef = new PoolDef();
poolDef.setDate_from(date);
poolDef.setName(poolList.getPoolList().get(i).getName());
poolDefRepository.save(poolDef);
Entity itself:
#Setter
#Getter
#EqualsAndHashCode(of = {"Id"})
#Transactional
#Entity
public class PoolDef {
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
private Long Id;
private String name;
#Column(name = "date_from", columnDefinition = "timestamp with time zone not null")
private OffsetDateTime date_from;
}
The only value that varies is the date_from. I do not know, why new entries are being added to the database and not just get updated. I have the #EqualsAndHashcode that are being built based on primary Id key, so the date_from should not matter. Every method invocation creates a new entry with a completely new Id...
your problem is your
GenerationType.IDENTITY
the documentation says:
Indicates that the persistence provider must assign primary keys for
the entity using a database identity column.
Now the key question is, what SQL is getting generated. Can you please trace the insert SQLs generated?
Also I would prefer to use SEQUENCES of databases. So I do not have to mess around with the Identities of the persistence provider and any application will behave the same against the database if you use the SEQUENCES of databases for your ID/primary key columns.
Also a issue could be your DDL for the table creation, but I assume you know how to define the database tables with the given constraints.
I am trying to have separate auto incremented id generator for each of my entities.
The target database is a SQL Server database, and I am using Hibernate 5.2.4.Final. Also I am generating the tables from code.
I have an abstract BaseEntity and other child entities like below, and thus, I am aiming for TABLE_PER_CLASS.
#Entity
#Inheritance(strategy = InheritanceType.TABLE_PER_CLASS)
public abstract class BaseEntity {
protected long id;
#Id
#GeneratedValue(strategy = GenerationType.XXX)
#Column(name = "Id")
public long getId() {
return id;
}
}
#Entity
#Table(name = "Tags")
public class Tag extends BaseEntity {
}
Below are the different scenarios that I have faced so far:
setting XXX to AUTO: Creates a hibernate_sequence table in database, which I assume, will not provide separate id sequence for separate table.
setting XXX to SEQUENCE: Same as above. Referred this, while doing it.
setting XXX to TABLE: Creates a hibernate_sequences table, which can provide separate id sequence for separate table. However, I have found out that this is quite expensive (same reference as above), and also not my preferred strategy.
setting XXX to TABLE: Does not work for TABLE_PER_CLASS.
What I actually want to use is the native identity column of SQL Server. However, using the SEQUENCE is also an option, but I am not sure how to create and use one for each table from hibernate. Please suggest how either one of these two can be achieved.
Update on the answer by Khalil M. I tried it in 2 possible ways:
applying on BaseEntity -> does not create a separate sequence for each table, and rather creates a ID_SEQNCE, which queried before saving every new entity. So, I am not sure how this is any different than using GenerationType.TABLE.
applying it on each individual entity class -> while saving, the generator creates duplicate id.
for creating a sequence use this
#Id
#GeneratedValue(generator = "ID_SEQ", strategy = GenerationType.SEQUENCE)
#SequenceGenerator(name = "ID_SEQ", sequenceName = "ID_SEQNCE",allocationSize=1)
Edit:
You have to make it by yourself because what you are asking is not supported in Table per class
the id has to be shared across several tables. Consequently, when
using this strategy, you should not use AUTO nor IDENTITY.
for more info
Use strategy = GenerationType.IDENTITY
A short example is below
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Column(name = "id", updatable = false, nullable = false)
private Long id;
The GenerationType.IDENTITY is the easiest to use but not the best one from a performance point of view. It relies on an auto-incremented database column and lets the database generate a new value with each insert operation. From a database point of view, this is very efficient because the auto-increment columns are highly optimized, and it doesn’t require any additional statements.
I have two tables (say table A and table B). Table B has foreign key from table A primary key. I generated my java entities using netbeans IDE and i now have something like:
For table A:
#Entity
#Table(name = "WORKFLOW_TRANSACTION")
public class WorkflowTransaction implements {
#OneToMany(mappedBy = "wtId")
private Collection<WorkflowTask> workflowTaskCollection;
#Id
#Basic(optional = false)
#NotNull
#Column(name = "APP_ID")
private BigDecimal appId;
.
.
.
For table B:
#Entity
#Table(name = "WORKFLOW_TASK")
public class WorkflowTask implements Serializable {
#JoinColumn(name = "WT_ID", referencedColumnName = "APP_ID")
#ManyToOne
private WorkflowTransaction wtId;
#Id
#Basic(optional = false)
#NotNull
#Column(name = "TASK_ID")
private BigDecimal taskId;
#Column(name = "STEP_NUM")
private BigInteger stepNum;
.
.
.
Now my questions are:
What is the correct way to save data, should I create object for table B entity and set it in table A entity and then save table A?
I am generating entity beans using netbeans IDE feature. Are there any known disadvantages of it?, if yes, what?
You have bi-directional association, so you need to setTable B property in Table A entity class and also vice-versa. Since you have not declared cascading, you need to save the Table A entity first and then Table B entity.
Alternatively, if you save Table B and then Table A entity classes, the hibernate generates an extra SQL update command to maintain the relationship.
But if you want hibernate to save Table B entity when you save Table A entity then you need to add Cascade property:
#OneToMany(mappedBy = "wtId", cascade=CascadeType.ALL)
I don't think you will have any disadvantages if you use Netbeans for generating the entity classes, it save you time in writing the entities. But if you want to learn then writing entities without Netbeans is good.
To achieve this you can use two type of techniques XML mapping or Annotations
In both these techniques the common point is use
cascade="save-update"
What happens is that you set an attribute in one table getter and it will automatically insert into the many relation when inserting into one relation table
Could somebody help me in setting appropriate annotation in hibernate for following case:
I have three tables:
Account, Card and AccountCard.
AccountCard is joining table for OneToMany relationship between Card and Account (account has many cards, card is attached to only one account).
I need to add to Account a List cards property and to Card model Account account property. This is the easy thing.
The problem is that I get "Cannot insert null value to AccountCard.id" while persisting Account with Cards.
Also I need to use sequence to generate IDs for joining table but don't know how.
Any help would be very appreciated.
Here is the code in Card:
#ManyToOne(fetch = FetchType.LAZY)
#JoinTable(name = "account_card", joinColumns = #JoinColumn(name = "crd_id"), inverseJoinColumns = #JoinColumn(name = "acc_id"))
private Account account;
I don't want to have a mapping in Account class so List cards is not added.
In your #JoinTable annotation, I see reference to an account_name table and not AccountCard. Is there actually an AccountCard table somewhere?
A join table usually doesn't need an id key of its own, and if you have hibernate autogenerate your table DDL it won't include one.
If you do indeed need an id on the join table, I don't think there's a way or a need to make hibernate aware of it, but you should make the column NOT NULL AUTO_INCREMENT in your SQL DDL.
Did you try to generate the tables first in the database (in my case mysql) and then create the entity with an ide like nebans? An auto increment id column in mysql then ends with:
#Id
#GeneratedValue(strategy = GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "ID")
private Integer id;
Check out http://netbeans.org/kb/docs/javaee/ecommerce/entity-session.html for a sample how to use netbeans to create entities from database
I'm using JPA toplink-essential and SQL Server 2008
My goal is to get auto-increment primary key value of the data that is going to be inserted into the table. I know in JDBC, there is getInsertedId() like method that give you the id of auto-increment primary id (but that's after the insert statement executed though)
In JPA, I found out #GenratedValue annotation can do the trick.
#Entity
#Table(name = "tableOne")
public class TableOne implements Serializable {
private static final long serialVersionUID = 1L;
#Id
#GeneratedValue(strategy=GenerationType.IDENTITY)
#Basic(optional = false)
#Column(name = "tableId")
private Integer tableId;
Now if I run the code below it should give me the auto incremented id but it returns NULL...
EntityManager em = EmProvider.getInstance().getEntityManagerFactory().createEntityManager();
EntityTransaction txn = em.getTransaction();
txn.begin();
TableOne parent = new TableOne();
em.persist(parent); //here I assume that id is pre-generated for me.
System.out.println(parent.getTableId()); //this returns NULL :(
The problem is you are using IDENTITY id generation. IDENTITY id generation cannot do preallocation as they require the INSERT to generate the id. TABLE and SEQUENCE id generation support preallocation, and I would always recommend usage of these, and never using IDENTITY because of this issue and because of performance.
You can trigger the id to be generated when using IDENTITY id generation by calling flush().
just simply do this :
public void create(T entity) {
getEntityManager().persist(entity);
getEntityManager().flush();
getEntityManager().refresh(entity);
}
After refreshing the entity you have the ID field with proper value.
We are also using SQL Server 2008 and it never worked for me so I always execute separate query "SELECT ##IDENTY" to get the inserted id.
The reason I found on the net was that auto id (IDENTITY) is managed by database and never fetched in Entity until unless you commit the row or manually retrieve the info from database.