can someone please explain me @MapsId in hibernate?

mapsid vs joincolumn
mapsid vs primarykeyjoincolumn
manytoone
mapsid onetoone example
mapsid multiple columns
mapsid with composite key
embeddable
mapsid baeldung

Can someone please explain to me @MapsId in hibernate? I'm having a hard time understanding it.

It would be great if one could explain it with an example and in what kind of use cases is it most applicable?

Here is a nice explanation from Object DB.

Designates a ManyToOne or OneToOne relationship attribute that provides the mapping for an EmbeddedId primary key, an attribute within an EmbeddedId primary key, or a simple primary key of the parent entity. The value element specifies the attribute within a composite key to which the relationship attribute corresponds. If the entity's primary key is of the same Java type as the primary key of the entity referenced by the relationship, the value attribute is not specified.

// parent entity has simple primary key

@Entity
public class Employee {
   @Id long empId;
   String name;
   ...
} 

// dependent entity uses EmbeddedId for composite key

@Embeddable
public class DependentId {
   String name;
   long empid;   // corresponds to primary key type of Employee
}

@Entity
public class Dependent {
   @EmbeddedId DependentId id;
    ...
   @MapsId("empid")  //  maps the empid attribute of embedded id
   @ManyToOne Employee emp;
}

Read the API Docs here.

can someone please explain me @MapsId in hibernate?, Here is a nice explanation from Object DB. Designates a ManyToOne or OneToOne relationship attribute that provides the mapping for an EmbeddedId primary� Example of @MapsId in Hibernate. By Arvind Rai, May 19, 2013 @MapsId in hibernate annotation maps a column with another table's column. @MapsId works with @Id and

I found this note also useful: @MapsId in hibernate annotation maps a column with another table's column.

It can be used also to share the same primary key between 2 tables.

Example:

@Entity
@Table(name = "TRANSACTION_CANCEL")
public class CancelledTransaction {
    @Id
    private Long id; // the value in this pk will be the same as the
                     // transaction line from transaction table to which 
                     // this cancelled transaction is related

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(name = "ID_TRANSACTION", nullable = false)
    @MapsId
    private Transaction transaction;
    ....
}

@Entity
@Table(name = "TRANSACTION")
@SequenceGenerator(name = "SQ_TRAN_ID", sequenceName = "SQ_TRAN_ID")
public class Transaction  {
    @Id
    @GeneratedValue(generator = "SQ_TRAN_ID", strategy = GenerationType.SEQUENCE)
    @Column(name = "ID_TRANSACTION", nullable = false)
    private Long id;
    ...
}

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As he explained Vladimir in his tutorial, The best way to map a @OneToOne relationship is to use @MapsId. This way, you don’t even need a bidirectional association since you can always fetch the Child entity by using the Parent entity identifier.

Hibernate Tips: How to Share the Primary Key in a One-to-One , Can someone please explain me @MapsId in hibernate ? I'm having a hard time understanding it. It would be great if one could explain it with� Annotation Type MapsId @Target(value={METHOD,FIELD}) @Retention(value=RUNTIME) public @interface MapsId Designates a ManyToOne or OneToOne relationship attribute that provides the mapping for an EmbeddedId primary key, an attribute within an EmbeddedId primary key, or a simple primary key of the parent entity.

MapsId lets you use the same primary key between two different entities/tables. Note: when you use MapsId, the CASCADE.ALL flag becomes useless, and you will need to make sure that your entities are saved manually.

javax.persistence.MapsId - JPA annotation, You can use JPA's @MapsId annotation to tell Hibernate that it shall use the foreign key of an associated entity as the primary key. Let's take a look at a simple example. Each Book has a Manuscript, and each Manuscript belongs to 1 Book. The foreign key of the Book is also the primary key of the Manuscript. Please explain the causes.From the javadoc of methods i know that. persist - Make an instance managed and persistent. merge - Merge the state of the given entity into the current persistence context. My question is more towards how hibernate manages the annotations.

IMHO, the best way to think about @MapsId is when you need to map a composite key in a n:m entity.

For instance, a customer can have one or more consultant and a consultant can have one or more customer:

And your entites would be something like this (pseudo Java code):

@Entity
public class Customer {
   @Id
   private Integer id;

   private String name;
}

@Entity
public class Consultant {
   @Id
   private Integer id;

   private String name;

   @OneToMany
   private List<CustomerByConsultant> customerByConsultants = new ArrayList<>();

   public void add(CustomerByConsultant cbc) {
      cbc.setConsultant(this);
      this.customerByConsultant.add(cbc);
   }
}

@Embeddable
public class ConsultantByConsultantPk implements Serializable {

    private Integer customerId;

    private Integer consultantId;
}

@Entity
public class ConsultantByConsultant {

   @EmbeddedId
   private ConsultantByConsultantPk id = new ConsultantByConsultantPk();

   @MapsId("customerId")
   @JoinColumn(insertable = false, updatable = false)
   Customer customer;

   @MapsId("consultantId")
   @JoinColumn(insertable = false, updatable = false)
   Consultant consultant;
}

Mapping this way, JPA automagically inserts Customer and Consultant ids in the EmbeddableId whenever you save a consultant. So you don't need to manually create the ConsultantByConsultantPk.

Hibernate One to One Mapping Annotation Example, @MapsId("empid") // maps the empid attribute of embedded id @ManyToOne as Hibernate (and HQL), EclipseLink, TopLink, OpenJPA and DataNucleus. 70 can someone please explain me @MapsId in hibernate? 41 what is a static interface in java? 29 Write a non-recursive traversal of a Binary Search Tree using constant space and O(n) run time

Bidirectional @OneToOne cascade issue JPA/Hibernate/Spring-Data, In this hibernate one to one mapping example, We will discuss 4 different variations. Table of In a bidirectional relationship, one of the sides (and only one) has to be the owner. The owner is In this approach, @MapsId is the main annotation to be used. Let see how Find me on Facebook and Twitter. Hibernate - Examples - Let us now take an example to understand how we can use Hibernate to provide Java persistence in a standalone application. We will go through the different step

How to change the @OneToOne shared primary key column name , There are many ways you can map a one-to-one relationship with Hibernate. can someone please explain me @MapsId in hibernate?, can someone please� (see can someone please explain me @MapsId in hibernate? for an explanation about MapsId) I also removed insertable=false and updatable=false. See below for the code. I didn't get MapsId to work with the StoryId class, so i changed the type of TaskPKID.storyId from StoryId to long.

Chapter 35. Mapping One-to-One Relationships, As previously explained, the one-to-one database table relationship requires the Primary Only when adding the @MapsId annotation will the JPA one-to-one This way, Hibernate will either generate or expect the following database tables: You have helped me sort out a few issues I was having and� how to use mapping file in hibernate and how to use configuration xml in hibernate, hibernate mapping file example and configuration xml file syntax, hibernate.cfg.xml Please consider disabling your ad blocker for Java4s.com, we won't encourage audio ads, popups or any other annoyances at any point, hope you support us :-) Thank you.

Comments
  • But what's so nice about it? Even without @MapsId, one can use JoinColumn to same effect, can he not? And if so, this example does not really tell what's this annotation really good for.
  • Since both entities will be sharing the same primary key, the entity with a column designated by @MapsId will in the persistence layer (database) only have primary key column. The idea is to share the primary key between the two entities.
  • What is an EmbeddedId primary key? How is it different from normal Primary Key?
  • "The value element specifies the attribute within a composite key to which the relationship attribute corresponds. " 1) What is meant by value element, please give an example? 2) What is a composite key? 3) What is the relationship attribute and give an example?
  • @MaksimGumerov it's efficient because you can fetch Dependent just by knowing identifier of Employee.
  • Where do I put @MapsId in a bidirectional association? Should both classes have @MapsId. Does it even make a difference?
  • I think one table will be the "owner" of the original pk (the one with @Id and @GeneratedValue and @Column) and have a @OneToOne and @JoinColumn with the other table, and the other table will have the @MapsId . However this probably wouldn't work if you wanted to INSERT into the 'other table' first.
  • Nice article about this way of usage (using id from another table as id of other entity) is here vladmihalcea.com/…
  • But if you want filter out transactions from canceled ones.. which is a common cause. How is this more efficient? I mean for SQL you just have to say NOT NULL for TRANSACTION.fk_cancelled_id but in this case, will be more operations.
  • In this specific case here, it is common to use a column like 'type' in the base class and table, where you'd identify if the transaction is of type 'cancel' or other.