Create Entities

Example

This sample Movie.java entity class defines a Movie entity that includes the following information:

• @Entity annotation that marks the class as a Hibernate ORM entity

• @Table annotation that maps the entity to the movies collection from the Atlas sample datasets

• @Id and @ObjectIdGenerator annotations that designate the id field as the primary key and configure automatic ObjectId generation

• Private fields that represent movie data

• Default and parameterized constructors for entity instantiation

• Getter and setter methods that provide access to the entity's fields

package org.example;
import com.mongodb.hibernate.annotations.ObjectIdGenerator;
import org.bson.types.ObjectId;
import jakarta.persistence.Entity;
import jakarta.persistence.Id;
import jakarta.persistence.Table;
@Entity
@Table(name = "movies")
public class Movie {
	@Id
	@ObjectIdGenerator
	private ObjectId id;
	private String title;
	private String plot;
	private int year;
	private String[] cast;
	public Movie(String title, String plot, int year, String[] cast) {
 		this.title = title;
		this.plot = plot;
		this.year = year;
		this.cast = cast;
 	}
	public Movie() {
	}
	public ObjectId getId() {
		return id;
	}
	public String getTitle() {
		return title;
	}
	public void setTitle(String title) {
		this.title = title;
	}
	public String getPlot() {
		return plot;
	}
	public void setPlot(String plot) {
		this.plot = plot;
	}
	
	public int getYear() {
		return year;
	}
	public void setYear(int year) {
		this.year = year;
	}
	public String[] getCast() {
		return cast;
	}
	
	public void setCast(String[] cast) {
		this.cast = cast;
	}
}

One-to-One Relationships

A One-to-One relationship is when a record in one database is associated with exactly one record in another database. In MongoDB, you can create a collection with an embedded document field to model a One-to-One relationship. The Hibernate ORM extension allows you to create embedded document fields by using @Struct aggregate embeddables.

The example defines a field with a @Struct aggregate embeddable type in an entity similar to the Define an Entity example in this guide. The sample Movie.java entity class includes the following information:

• @Entity and @Table annotations that define the entity and map it to the movies collection

• @Id and @ObjectIdGenerator annotations that designate the id field as the primary key

• String field that represents the movie's title

• @Struct aggregate embeddable fields that represent movie awards and studio information

The following example represents a One-to-One relationship because each Movie entity is associated with one Awards embeddable and one Studio embeddable:

@Entity
@Table(name = "movies")
public class Movie {
    @Id
    @ObjectIdGenerator
    private ObjectId id;
    private String title;
    private Awards awards;
    private Studio studio;
    public Movie(String title, Awards awards, Studio studio) {
        this.title = title;
        this.awards = awards;
        this.studio = studio;
    }
    public Movie() {
    }
    // Getter and setter methods
}

The following sample code creates an Awards @Struct aggregate embeddable:

@Embeddable
@Struct(name = "Awards")
public class Awards {
    private int wins;
    private int nominations;
    private String text;
    public Awards(int wins, int nominations, String text) {
       this.wins = wins;
       this.nominations = nominations;
       this.text = text;
    }
    public Awards() {
    }
    // Getter and setter methods
}

The following sample code creates a Studio @Struct aggregate embeddable:

@Embeddable
@Struct(name = "Studio")
public class Studio {
    private String name;
    private String location;
    private int foundedYear;
    public Studio(String name, String location, int foundedYear) {
        this.name = name;
        this.location = location;
        this.foundedYear = foundedYear;
    }
    public Studio() {
    }
    // Getter and setter methods
}

One-to-Many Relationships

A One-to-Many relationship is when a record in one database is associated with many records in another database. In MongoDB, you can define a collection field that stores a list of embedded documents to model a One-to-Many relationship. The Hibernate ORM extension allows you to create embedded document fields by using a list of @Struct aggregate embeddables.

The example defines a field that stores a list of @Struct aggregate embeddables in an entity similar to the Define an Entity Example in this guide. The sample Movie.java entity class includes the following information:

• @Entity and @Table annotations that define the entity and map it to the movies collection

• @Id and @ObjectIdGenerator annotations that designate the id field as the primary key

• String field that represents the movie's title

• List field that stores multiple Writer @Struct aggregate embeddables, which represents writer information

The following example represents a One-to-Many relationship because each Movie entity is associated with multiple Writer embeddables:

@Entity
@Table(name = "movies")
public class Movie {
    @Id
    @ObjectIdGenerator
    @Column(name = "_id")
    private ObjectId id;
    private String title;
    private List<Writer> writers;
    public Movie(String title, List<Writer> writers) {
        this.title = title;
        this.writers = writers;
    }
    public Movie() {
    }
    // Getter and setter methods
}

The following sample code creates a Writer @Struct aggregate embeddable:

@Embeddable
@Struct(name = "Writer")
public class Writer {
    private String name;
    public Writer() {
    }
    public Writer(String name) {
        this.name = name;
    }
    // Getter and setter methods
}