The class generated by Java – querydsl cannot access the second level element for query

I use querydsl with spring data JPA in my java project, and use the file generated by querydsl Maven plug-in to use the querydsl model class generated by it This is useful when I use it for a level of nested objects, but if I try to access a second level access object, it will give a NullPointerException to keep the second level model object uninitialized

I'll thank you for some help

I'm on the third line qmachine Received a NullPointerException when vendor is null

QTransaction qtransaction = QTransaction.transaction;
QMachine qmachine = qtransaction.machine;
BooleanExpression vendorexp = qmachine.vendor.vendor.eq(machineType);

My mapping course is as follows: Trading

@Entity
@Table(name = "dsdsd")
public class Transaction extends AbstractPersistable<Long> {

    private static final long serialVersionUID = 1L;

    @ManyToOne
    @JoinColumn(name = "machine_id")
    private Machine machine;

}

The machine types are:

@Entity
@Table(name="machine")
public class Machine extends AbstractPersistable<Long> {

    private static final long serialVersionUID = 1L;

    @ManyToOne
    @JoinColumn(name="vendor_id")
    private Vendor vendor;
}

And vendor classes are

@Entity
@Table(name="vendors")
public class Vendor extends AbstractPersistable<Long> {

    private static final long serialVersionUID = 1L;

    @Column(name="vendor")
    @Enumerated(EnumType.STRING)
    private VendorType vendor;

}

I have deliberately mentioned smokers and drug addicts

Solution

By default, only the first level is initialized For initialization options, see the section of this document: http://www.querydsl.com/static/querydsl/3.6.0/reference/html/ch03s03.html#d0e2192

Due to the possibility of infinite loop, the final field cannot be fully initialized, but querydsl also provides the option of property accessor method