1. CONACYT - Arquitectura
2. Lineamientos para Back-End

Relaciones con JPA

A continuación se muestran ejemplos de cómo se deberían anotar dos entidades relacionadas entre sí según el tipo de relación entre ellas. Para este ejemplo se suponen dos entidades llamadas Left (Izquierda) y Derecha. También se muestra la vista de estas entidades y su relación en UML y en un modelo de datos físico.

Relaciones con JPA

Relaciones Unidireccionales

Uno a Uno Unidireccional

UML

Modelo de Datos

Llaves Foráneas:

• De la tabla lefts a la tabla rights: fk_lefts.att_right_id_rights.id

Java (POJO)

    @Entity
    @Table(name = "lefts")
    public class Left implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @OneToOne
        @JoinColumn(name = "att_right_id", unique = true)
        private Right attRight;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

        public Right getAttRight() {
            return attRight;
        }

        public void setAttRight(Right attRight) {
            this.attRight = attRight;
        }

    }

    @Entity
    @Table(name = "rights")
    public class Right implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

    }

Uno a Muchos Unidireccional

UML

!No soportada!
En este tipo de relación, la entidad Left debe ser siempre navegable desde la entidad Right.
Este caso sería el mismo que la relación Bidireccional Uno a Muchos

Muchos a Uno Unidireccional

UML

Modelo de Datos

Llaves Foráneas:

• De la tabla lefts a la tabla rights: fk_lefts.att_right_id_rights.id

Java (POJO)

    @Entity
    @Table(name = "lefts")
    public class Left implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @ManyToOne
        @JoinColumn(name = "att_right_id")
        private Right attRight;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

        public Right getAttRight() {
            return attRight;
        }

        public void setAttRight(Right attRight) {
            this.attRight = attRight;
        }

    }

    @Entity
    @Table(name = "rights")
    public class Right implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

    }

Muchos a Muchos Unidireccional

UML

Data Model

Llaves Foráneas:

• De la tabla lefts_atts_right a la tabla lefts: fk_lefts_atts_right.left_id_lefts.id
• De la tabla lefts_atts_right a la tabla rights: fk_lefts_atts_right.att_right_id.rights.id

Java (POJO)

    @Entity
    @Table(name = "lefts")
    public class Left implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @ManyToMany
        @JoinTable(name = "lefts_atts_right", 
        joinColumns = JoinColumn(name="left_id", referencedColumnName="id"),
        inverseJoinColumns = 
        @JoinColumn(name="att_right_id", referencedColumnName="id"))
        private Set<Right> attsRight = new HashSet<>();

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

        public Set<Right> getAttsRight() {
            return attsRight;
        }

        public void setAttsRight(Set<Right> attsRight) {
            this.attsRight = attsRight;
        }

        public Left addAttRight (Right attsRight) {
            this.attsRight.add(attsRight);
            attsRight.getLeft().add(this);
            return this;
        }

        public Left removeAttRight(Right attsRight) {
            this.attsRight.remove(attsRight);
            attsRight.getLeft().remove(this);
            return this;
        } 

    }

    @Entity
    @Table(name = "rights")
    public class Right implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
            this.id = id;
        } 

    }

Relaciones Bidireccionales

Uno a Uno Bidireccional

UML

Data Model

LLaves Foráneas:

• De la tabla lefts a la tabla rights: fk_lefts.att_right_id_rights.id

Java (POJO)

    @Entity
    @Table(name = "lefts")
    public class Left implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @OneToOne
        @JoinColumn(name = "att_right_id", unique = true)
        private Right attRight;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

        public Right getAttRight() {
            return attRight;
        }

        public void setAttRight(Right attRight) {
            this.attRight = attRight;
        }

    }

    @Entity
    @Table(name = "rights")
    public class Right implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @OneToOne(mappedBy = "attRight")
        private Left attLeft;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }    
        
        public Left getAttLeft() {
            return attLeft;
        }

        public void setAttLeft(Left attLeft) {
            this.attLeft = attLeft;
        }

    }

Uno a Muchos Bidireccional

UML

Modelo de Datos

Llaves Foráneas:

• De la tabla rights a la tabla lefts: fk_rights.att_left_id_lefts.id

Java (POJO)

    @Entity
    @Table(name = "lefts")
    public class Left implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @OneToMany(mappedBy = "attLeft")
        @JsonIgnore
        private Set<Right> attsRight = new HashSet<>();

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

        public Set<Right> getAttsRight() {
            return attsRight;
        }

        public void setAttsRight(Set<Right> attsRight) {
            this.attsRight = attsRight;
        }

        public Left addAttRight (Right attRight) {
            this.attsRight.add(attRight);
            attRight.getLeft().add(this);
            return this;
        }

        public Left removeAttRight(Right attRight) {
            this.attsRight.remove(attRight);
            attRight.getLeft().remove(this);
            return this;
        } 

    }

    @Entity
    @Table(name = "rights")
    public class Right implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @ManyToOne
        @JoinColumn(name = "att_left_id")
        private Left attLeft;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }    
        
        public Left getAttLeft() {
            return attLeft;
        }

        public void setAttLeft(Left attLeft) {
            this.attLeft = attLeft;
        }

    }

Muchos a Uno Bidireccional

UML

Modelo de Datos

Llaves Foráneas:

• De la tabla lefts a la tabla rights: fk_lefts.att_right_id_rights.id

Java (POJO)

    @Entity
    @Table(name = "lefts")
    public class Left implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @ManyToOne
        @JoinColumn(name = "att_right_id")
        private Right attRight;

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

        public Right getAttRight() {
            return attRight;
        }

        public void setAttRight(Right attRight) {
            this.attRight = attRight;
        }

    }

    @Entity
    @Table(name = "rights")
    public class Right implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @OneToMany(mappedBy = "attRight")
        private Set<Left> attsLeft = new HashSet<>();

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }	    
        
        public Set<Left> getAttsLeft() {
            return attsLeft;
        }

        public void setAttsLeft(Set<Left> attsLeft) {
            this.attsLeft = attsLeft;
        }

    }

Muchos a Muchos Bidireccional

UML

Modelo de Datos

Llaves Foráneas:

• De la tabla atts_left_atts_right a la tabla lefts: fk_atts_left_atts_right.att_left_id_lefts.id
• De la tabla atts_left_atts_right a la tabla rights: fk_atts_left_atts_right.att_right_id.rights.id

Java (POJO)

    @Entity
    @Table(name = "lefts")
    public class Left implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @ManyToMany
        @JoinTable(name = "atts_left_atts_right", 
        joinColumns = JoinColumn(name="att_left_id", referencedColumnName="id"),
        inverseJoinColumns = 
        @JoinColumn(name="att_right_id", referencedColumnName="id"))
        private Set<Right> attsRight = new HashSet<>();

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

        public Set<Right> getAttsRight() {
            return attsRight;
        }

        public void setAttsRight(Set<Right> attsRight) {
            this.attsRight = attsRight;
        }

        public Left addAttRight (Right attsRight) {
            this.attsRight.add(attsRight);
            attsRight.getLeft().add(this);
            return this;
        }

        public Left removeAttRight(Right attsRight) {
            this.attsRight.remove(attsRight);
            attsRight.getLeft().remove(this);
            return this;
        } 

    }

    @Entity
    @Table(name = "rights")
    public class Right implements Serializable {
        private static final long serialVersionUID = 1L;

        @Id
        @GeneratedValue(strategy = GenerationType.IDENTITY)
        @Column(name = "id", unique = true, nullable = false)
        private Long id;

        @ManyToMany(mappedBy = "attsRight")
        @JsonIgnore
        private Set<Left> attsLeft = new HashSet<>();

        public Long getId() {
            return id;
        }

        public void setId(Long id) {
        this.id = id;
        }

        public Set<Left> getLefts() {
            return attsLeft;
        }

        public void setLefts(Set<Left> attsLeft) {
            this.attsLeft = attsLeft;
        }

        public Right addLeft(Left left) {
            this.attsLeft.add(left);
            left.getAttsRight().add(this);
            return this;
        }

        public Right removeLeft(Lefts left) {
            this.lefts.remove(left);
            lefts.getAttsRight().remove(this);
            return this;
        }  

    }

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