hibernate - one to one mapping using primary key join column -

i have employee , employee detail classes mapped (bi directional) using primary key join column (employee_id)

@entity @table(name="employee") public class employee {  @id @generatedvalue @column(name="employee_id") private long employeeid;  @column(name="firstname") private string firstname;  @column(name="lastname") private string lastname;  @column(name="birth_date") @temporal(value = temporaltype.date ) private date birthdate;  @column(name="cell_phone") private string cellphone;  @onetoone(mappedby="empl", cascade=cascadetype.all) private employeedetail employeedetail;  ... }    @table(name="employeedetail") public class employeedetail {   @id @column(name="employee_id", unique=true, nullable=false) @generatedvalue(generator="gen") @genericgenerator(name="gen", strategy="foreign", parameters=@parameter(name="property", value="empl")) private long employeeid;  @column(name="street") private string street;  @column(name="city") private string city;  @column(name="state") private string state;  @column(name="country") private string country;  @onetoone @primarykeyjoincolumn private employee empl; .................... } 

can please clarify why when executing following query session.createquery("from employee").list();

a) join queries 2),3) , 4) executed fetch data employeedetail? why not directly fetch employeedetail table using employeeid value in employee object without join?

1) hibernate: select employee0_.employee_id employee1_0_, employee0_.birth_date birth_da2_0_, employee0_.cell_phone cell_pho3_0_, employee0_.firstname firstnam4_0_, employee0_.lastname lastname5_0_ employee employee0_   2) hibernate: select employeede0_.employee_id employee1_1_0_, employeede0_.city city2_1_0_, employeede0_.country country3_1_0_, employeede0_.state state4_1_0_, employeede0_.street street5_1_0_, employee1_.employee_id employee1_0_1_, employee1_.birth_date birth_da2_0_1_, employee1_.cell_phone cell_pho3_0_1_, employee1_.firstname firstnam4_0_1_, employee1_.lastname lastname5_0_1_ employeedetail employeede0_ left outer join employee employee1_ on employeede0_.employee_id=employee1_.employee_id employeede0_.employee_id=?  3) hibernate: select employeede0_.employee_id employee1_1_0_, employeede0_.city city2_1_0_, employeede0_.country country3_1_0_, employeede0_.state state4_1_0_, employeede0_.street street5_1_0_, employee1_.employee_id employee1_0_1_, employee1_.birth_date birth_da2_0_1_, employee1_.cell_phone cell_pho3_0_1_, employee1_.firstname firstnam4_0_1_, employee1_.lastname lastname5_0_1_ employeedetail employeede0_ left outer join employee employee1_ on employeede0_.employee_id=employee1_.employee_id employeede0_.employee_id=?  4) hibernate: select employeede0_.employee_id employee1_1_0_, employeede0_.city city2_1_0_, employeede0_.country country3_1_0_, employeede0_.state state4_1_0_, employeede0_.street street5_1_0_, employee1_.employee_id employee1_0_1_, employee1_.birth_date birth_da2_0_1_, employee1_.cell_phone cell_pho3_0_1_, employee1_.firstname firstnam4_0_1_, employee1_.lastname lastname5_0_1_ employeedetail employeede0_ left outer join employee employee1_ on employeede0_.employee_id=employee1_.employee_id employeede0_.employee_id=?  

b) also, query session.createquery("from employeedetail").list();

why employee info fetched per below select queries instead of being proxied?    hibernate: select employeede0_.employee_id employee1_1_, employeede0_.city city2_1_, employeede0_.country country3_1_, employeede0_.state state4_1_, employeede0_.street street5_1_ employeedetail employeede0_   hibernate: select employee0_.employee_id employee1_0_0_, employee0_.birth_date birth_da2_0_0_, employee0_.cell_phone cell_pho3_0_0_, employee0_.firstname firstnam4_0_0_, employee0_.lastname lastname5_0_0_ employee employee0_ employee0_.employee_id=?  hibernate: select employee0_.employee_id employee1_0_0_, employee0_.birth_date birth_da2_0_0_, employee0_.cell_phone cell_pho3_0_0_, employee0_.firstname firstnam4_0_0_, employee0_.lastname lastname5_0_0_ employee employee0_ employee0_.employee_id=?  hibernate: select employee0_.employee_id employee1_0_0_, employee0_.birth_date birth_da2_0_0_, employee0_.cell_phone cell_pho3_0_0_, employee0_.firstname firstnam4_0_0_, employee0_.lastname last`enter code here`name5_0_0_ employee employee0_ employee0_.employee_id=? 

a) little bit weird, , hibernate better. however, due fact employee loaded eagerly in employeedetail, , hibernate wants avoid additional queries load corresponding employee each employeedetail. better because corresponding employees loaded first query.

this should disappear if apply advice in b).

b) default, one-to-one associations eager in jpa. make lazy:

@onetoone(fetch = fetchtype.lazy) @primarykeyjoincolumn private employee empl; 

however, keep in mind behavior of one-to-one associations described here. if hibernate cannot determine whether proxied object in one-to-one relation exists or null, additional query executed anyway check this.

to overcome this, if empl mandatory each employeedetail (and in use case, employee detail cannot exist without employee), indicate in association mapping:

@onetoone(fetch = fetchtype.lazy, optional = false) @primarykeyjoincolumn private employee empl; 

this way hibernate make proxy containing employee id when loading employeedetail entity instances without querying employee table @ all.