CREATE TABLE unit
(
  id BIGINT PRIMARY KEY AUTO_INCREMENT,
  code VARCHAR(20) UNIQUE NOT NULL,
  description VARCHAR(100) NOT NULL
);

CREATE TABLE building
(
  id BIGINT PRIMARY KEY AUTO_INCREMENT,
  code VARCHAR(20) UNIQUE NOT NULL,
  name VARCHAR(100) NOT NULL,
  latitude  NUMERIC(8,6),
  longitude NUMERIC(8,6)
);

CREATE TABLE link_unit_building
(
  id BIGINT PRIMARY KEY AUTO_INCREMENT,
  unit_id BIGINT NOT NULL,
  building_id BIGINT NOT NULL
);

ALTER TABLE link_unit_building ADD(
 CONSTRAINT building_fk
 FOREIGN KEY (building_id)
 REFERENCES building(id)
  ON DELETE CASCADE ON UPDATE CASCADE,
 CONSTRAINT unit_fk
 FOREIGN KEY (unit_id)
 REFERENCES unit (id)
 ON DELETE CASCADE ON UPDATE CASCADE);


----------------------------------------------------------------------------------------------------------------------------------
package zesp03.entity;

import javax.persistence.*;

/**
 * Created by Berent on 2017-02-20.
 */

@Entity
@Table(name = "unit")
public class Unit {

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(length = 20, unique = true, nullable = false)
    private String code;

    @Column(length = 100, nullable = false)
    private String description;


}

----------------------------------------------------------------------------------------------------------------------------------

package zesp03.entity;
import javax.persistence.*;

/**
 * Created by Berent on 2017-02-20.
 */

@Entity
@Table(name = "building")
public class Building {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(length = 20, unique = true, nullable = false)
    private String code;

    @Column(length = 100, nullable = false)
    private String name;

    @Column(precision=8, scale=6)
    private Number latitude;

    @Column(precision=8, scale=6)
    private Number longitude;


}

---------------------------------------------------------------------------------------------------------------------------
package zesp03.entity;

import javax.persistence.*;

/**
 * Created by Berent on 2017-02-20.
 */

@Entity
@Table(name = "link_unit_building")
public class Link_unit_building {
    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    private Long id;

    @Column(nullable = false)
    private Long unit_id;

    @Column(nullable = false)
    private Long building_id;

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(
            name = "building_id",
            foreignKey = @ForeignKey(name = "building_fk"),
            nullable = false,
            unique = true
    )
    private Building building;

    @OneToOne(fetch = FetchType.LAZY)
    @JoinColumn(
            name = "unit_id",
            foreignKey = @ForeignKey(name = "unit_fk"),
            nullable = false,
            unique = true
    )
    private Unit unit;


}