Hibernate - @ElementCollection relation with composite key practical example (java, complex key, OneToMany, @EmbeddedId, @CollectionTable, @Embeddable)

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// -----------------------------------------------------------
// SomeBaseEntity.java
// -----------------------------------------------------------

import javax.persistence.CollectionTable;
import javax.persistence.Column;
import javax.persistence.ElementCollection;
import javax.persistence.EmbeddedId;
import javax.persistence.Entity;
import javax.persistence.EnumType;
import javax.persistence.Enumerated;
import javax.persistence.FetchType;
import javax.persistence.JoinColumn;
import javax.persistence.Table;

@Setter
@Getter
@NoArgsConstructor
@EqualsAndHashCode(onlyExplicitlyIncluded = true)
@Entity
@Table(name = "some_base_table")
public class SomeBaseEntity {

    @EmbeddedId
    @EqualsAndHashCode.Include
    private SomeCompositeKey someCompositeKey; // 3 fields - field_1, field_2, field_3

    // ... some other columns

    // instead of using OneToMany and foreign key in native SQL table schema
    // we use hibernate mechanism to manage below relation for us
    @ElementCollection(fetch = FetchType.EAGER)
    @CollectionTable(name = "some_table",
            joinColumns = {
                    // those 3 x fields are fields of SomeCompositeKey
                    @JoinColumn(name = "field_1", referencedColumnName = "field_1"),
                    @JoinColumn(name = "field_2", referencedColumnName = "field_2"),
                    @JoinColumn(name = "field_3", referencedColumnName = "field_3")
            })
    List<SomeEntity> someField;

}


// -----------------------------------------------------------
// SomeEntity.java
// -----------------------------------------------------------

import javax.persistence.Column;
import javax.persistence.Embeddable;

@Embeddable
@Data
@NoArgsConstructor
public class SomeEntity {

    // we do not define 3 fields - field_1, field_2, field_3
    // also we do not add those fields as foreign key in native SQL table schema
    // hibernate will manage it by itself

    @Column(name = "field_4")
    private Long field4;

    @Column(name = "field_5")
    private Long field4;
}


// -----------------------------------------------------------
// SomeCompositeKey.java
// -----------------------------------------------------------

import javax.persistence.Column;
import javax.persistence.Embeddable;

@Embeddable
@Data
@NoArgsConstructor
public class SomeCompositeKey {

    @Column(name = "field_1")
    private Long field1;

    @Column(name = "field_2")
    private Long field2;

    @Column(name = "field_3")
    private Long field3;

}


// -----------------------------------------------------------
// database schmea
// -----------------------------------------------------------

DROP TABLE IF EXISTS some_base_table;
CREATE TABLE some_base_table
(
    field_1 BIGINT(20) NOT NULL,
    field_2 BIGINT(20) NOT NULL,
    field_3 BIGINT(20) NOT NULL,
    PRIMARY KEY (field_1, field_3, field_3)
) COLLATE = 'utf8_general_ci'
ENGINE = InnoDB;


-- we do not define foreign key in database schema
DROP TABLE IF EXISTS some_table;
CREATE TABLE some_table
(
    field_1 BIGINT(20) NOT NULL,
    field_2 BIGINT(20) NOT NULL,
    field_3 BIGINT(20) NOT NULL,
    field_4 BIGINT(20) NOT NULL,
    field_5 BIGINT(20) NOT NULL
) COLLATE = 'utf8_general_ci'
ENGINE = InnoDB;