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POCan someone please explain mappedBy in hibernate?
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  1. POCan someone please explain mappedBy in hibernate?
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    copied!<p>I am new to hibernate and need to use one-to-many and many-to-one relations. It is a bi-directional relationship in my objects, so that I can traverse from either direction. <code>mappedBy</code> is the recommended way to go about it, however, I couldn't understand it. Can someone please explain to me :</p> <ul> <li>what is the recommended way to use it ?</li> <li>what purpose does it solve ?</li> </ul> <p>For the sake of my example, here are my classes with annotations :</p> <ul> <li><code>Airline</code> <strong>OWNS many</strong> <code>AirlineFlights</code></li> <li><strong>Many</strong> <code>AirlineFlights</code> belong to <strong>ONE</strong> <code>Airline</code></li> </ul> <p><strong>Airline</strong>:</p> <pre><code>@Entity @Table(name="Airline") public class Airline { private Integer idAirline; private String name; private String code; private String aliasName; private Set&lt;AirlineFlight&gt; airlineFlights = new HashSet&lt;AirlineFlight&gt;(0); public Airline(){} public Airline(String name, String code, String aliasName, Set&lt;AirlineFlight&gt; flights) { setName(name); setCode(code); setAliasName(aliasName); setAirlineFlights(flights); } @Id @GeneratedValue(strategy=GenerationType.IDENTITY) @Column(name="IDAIRLINE", nullable=false) public Integer getIdAirline() { return idAirline; } private void setIdAirline(Integer idAirline) { this.idAirline = idAirline; } @Column(name="NAME", nullable=false) public String getName() { return name; } public void setName(String name) { this.name = DAOUtil.convertToDBString(name); } @Column(name="CODE", nullable=false, length=3) public String getCode() { return code; } public void setCode(String code) { this.code = DAOUtil.convertToDBString(code); } @Column(name="ALIAS", nullable=true) public String getAliasName() { return aliasName; } public void setAliasName(String aliasName) { if(aliasName != null) this.aliasName = DAOUtil.convertToDBString(aliasName); } @OneToMany(fetch=FetchType.LAZY, cascade = {CascadeType.ALL}) @JoinColumn(name="IDAIRLINE") public Set&lt;AirlineFlight&gt; getAirlineFlights() { return airlineFlights; } public void setAirlineFlights(Set&lt;AirlineFlight&gt; flights) { this.airlineFlights = flights; } } </code></pre> <p><strong>AirlineFlights:</strong></p> <pre><code>@Entity @Table(name="AirlineFlight") public class AirlineFlight { private Integer idAirlineFlight; private Airline airline; private String flightNumber; public AirlineFlight(){} public AirlineFlight(Airline airline, String flightNumber) { setAirline(airline); setFlightNumber(flightNumber); } @Id @GeneratedValue(generator="identity") @GenericGenerator(name="identity", strategy="identity") @Column(name="IDAIRLINEFLIGHT", nullable=false) public Integer getIdAirlineFlight() { return idAirlineFlight; } private void setIdAirlineFlight(Integer idAirlineFlight) { this.idAirlineFlight = idAirlineFlight; } @ManyToOne(fetch=FetchType.LAZY) @JoinColumn(name="IDAIRLINE", nullable=false) public Airline getAirline() { return airline; } public void setAirline(Airline airline) { this.airline = airline; } @Column(name="FLIGHTNUMBER", nullable=false) public String getFlightNumber() { return flightNumber; } public void setFlightNumber(String flightNumber) { this.flightNumber = DAOUtil.convertToDBString(flightNumber); } } </code></pre> <p><strong>EDIT:</strong></p> <p>Database schema:</p> <p>AirlineFlights has the idAirline as ForeignKey and Airline has no idAirlineFlights. This makes, AirlineFlights as the owner/identifying entity ?</p> <p>Theoretically, I would like airline to be the owner of airlineFlights.</p> <p><img src="https://i.stack.imgur.com/gQvDs.png" alt="enter image description here"></p>
 

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