休眠条件查询创建多个SQL

Question

I am facing a very strange issue with hibernate criteria in my application. Below mentioned in the snippet from my source code.

Entity Class

    import java.io.Serializable;

import javax.persistence.Column;
import javax.persistence.Entity;
import javax.persistence.GeneratedValue;
import javax.persistence.GenerationType;
import javax.persistence.Id;
import javax.persistence.Table;

import org.hibernate.annotations.Cache;
import org.hibernate.annotations.CacheConcurrencyStrategy;

@Entity
@Table(name = "AIRPORT")
@Cache(usage = CacheConcurrencyStrategy.READ_ONLY)
public class Airport implements Serializable {

    private static final long serialVersionUID = -7120581694566566178L;
    private Long id;
    private String countryCode;
    private String countryName;
    private String cityCode;
    private String cityName;
    private String airportCode;
    private String airportName;

    @Id
    @GeneratedValue(strategy = GenerationType.IDENTITY)
    @Column(name = "ID", unique = true)
    public Long getId() {
        return id;
    }

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

    @Column(name = "COUNTRY_NAME")
    public String getCountryName() {
        return countryName;
    }

    public void setCountryName(String countryName) {
        this.countryName = countryName;
    }

    @Column(name = "COUNTRY_CODE", length = 10)
    public String getCountryCode() {
        return countryCode;
    }

    public void setCountryCode(String countryCode) {
        this.countryCode = countryCode;
    }

    @Column(name = "CITY_CODE", length = 25)
    public String getCityCode() {
        return cityCode;
    }

    public void setCityCode(String cityCode) {
        this.cityCode = cityCode;
    }

    @Column(name = "CITY_NAME")
    public String getCityName() {
        return cityName;
    }

    public void setCityName(String cityName) {
        this.cityName = cityName;
    }

    @Column(name = "AIRPORT_CODE", unique = true, length = 10)
    public String getAirportCode() {
        return airportCode;
    }

    public void setAirportCode(String airportCode) {
        this.airportCode = airportCode;
    }

    @Column(name = "AIRPORT_NAME")
    public String getAirportName() {
        return airportName;
    }

    public void setAirportName(String airportName) {
        this.airportName = airportName;
    }
}

DAO Class

    Criteria criteria = getSession().createCriteria(getTemplateClass());
    criteria.addOrder(Order.asc("countryCode"));
    criteria.addOrder(Order.asc("cityCode"));
    criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);
    criteria.setCacheable(true);
    return (List<Airport>) criteria.list();

Generated SQL when starting application and querying result

Hibernate: select this_.ID as ID1_12_0_, this_.AIRPORT_CODE as AIRPORT_2_12_0_, this_.AIRPORT_NAME as AIRPORT_3_12_0_, this_.CITY_CODE as CITY_COD4_12_0_, this_.CITY_NAME as CITY_NAM5_12_0_, this_.COUNTRY_CODE as COUNTRY_6_12_0_, this_.COUNTRY_NAME as COUNTRY_7_12_0_ from AIRPORT this_ order by this_.COUNTRY_CODE asc, this_.CITY_CODE asc

If I call same code again and suppose I have 1000 airports list then it executes below query for 1000 times. This behavior is quite strange.

Hibernate: select airport0_.ID as ID1_12_0_, airport0_.AIRPORT_CODE as AIRPORT_2_12_0_, airport0_.AIRPORT_NAME as AIRPORT_3_12_0_, airport0_.CITY_CODE as CITY_COD4_12_0_, airport0_.CITY_NAME as CITY_NAM5_12_0_, airport0_.COUNTRY_CODE as COUNTRY_6_12_0_, airport0_.COUNTRY_NAME as COUNTRY_7_12_0_ from AIRPORT airport0_ where airport0_.ID=?
Hibernate: select airport0_.ID as ID1_12_0_, airport0_.AIRPORT_CODE as AIRPORT_2_12_0_, airport0_.AIRPORT_NAME as AIRPORT_3_12_0_, airport0_.CITY_CODE as CITY_COD4_12_0_, airport0_.CITY_NAME as CITY_NAM5_12_0_, airport0_.COUNTRY_CODE as COUNTRY_6_12_0_, airport0_.COUNTRY_NAME as COUNTRY_7_12_0_ from AIRPORT airport0_ where airport0_.ID=?
Hibernate: select airport0_.ID as ID1_12_0_, airport0_.AIRPORT_CODE as AIRPORT_2_12_0_, airport0_.AIRPORT_NAME as AIRPORT_3_12_0_, airport0_.CITY_CODE as CITY_COD4_12_0_, airport0_.CITY_NAME as CITY_NAM5_12_0_, airport0_.COUNTRY_CODE as COUNTRY_6_12_0_, airport0_.COUNTRY_NAME as COUNTRY_7_12_0_ from AIRPORT airport0_ where airport0_.ID=?
........
........

Even I am using ehcache and even the below line in my criteria.

criteria.setResultTransformer(Criteria.DISTINCT_ROOT_ENTITY);

Any help would be greatly appreciated.

Answer 1

I can think of a few different reasons why this might be occuring:

1. Your entity has an association defined in it that is configured to eager join by default and you have also specified that the association use FetchMode.SELECT . (This is known as the N+1 Problem)

2. While the transaction is still open, you are interacting with an association of each Airport object that is set to lazy load. By interacting, I mean, you are using a getter to access the relation, forcing Hibernate to deproxy the associated entity. Since the deproxying is occurring with the transaction still open and the associated entity has not yet been loaded, Hibernate automatically fetches the association for you.

3. You have written your Airport entity's hashcode or equals methods to use a property of an association that is not eagerly joined and forces hibernate to deproxy, and thus fetch the unloaded entity, while within the transaction.