{"id":106686,"date":"2020-09-05T15:15:00","date_gmt":"2020-09-05T12:15:00","guid":{"rendered":"https:\/\/www.javacodegeeks.com\/?p=106686"},"modified":"2020-09-02T16:18:36","modified_gmt":"2020-09-02T13:18:36","slug":"spring-boot-data-jpa-query-for-nested-object","status":"publish","type":"post","link":"https:\/\/www.javacodegeeks.com\/2020\/09\/spring-boot-data-jpa-query-for-nested-object.html","title":{"rendered":"Spring boot data JPA – Query for nested object"},"content":{"rendered":"

Nowadays spring boot and spring data are widely used frameworks. If you are building web application in java, spring boot is the first choice. If you have Database then spring data JPA is best choice. In spring boot spring data is the default implementation for database interaction. Spring boot using spring data JPA even creates nested object query from method name.<\/p>\n

Therefore, if you are using spring boot or spring data JPA, you must know how queries are created specially if you have nested object structure. <\/p>\n

Introduction<\/h2>\n

Spring data JPA provides repository abstraction and reduces the boiler plate code from persistence layers. As discussed in our previous blog Spring data Java beginner<\/a>, we can define queries in two ways, Query annotation and Method name itself.<\/p>\n

For simple use cases method name for query resolution is best option. However, using spring boot for nested object property without knowing how it works, could cause big issue at runtime.<\/p>\n

Lets understand what could be the problem in nested object query and how can we resolve it.<\/p>\n

Problem statement<\/h2>\n

For example if you create method findByDepartmentId, what will be the query? It would be either,<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n<\/td>\n
\n
\n
Select * from ClassRoom where departmentId=?<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

OR<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n<\/td>\n
\n
\n
Select * from ClassRoom c left join department d on <condition> where d.id =?<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

Both are the possibilities depending on the class structure like<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n<\/td>\n
\n
\n
Class ClassRoom {<\/code><\/div>\n
   <\/code>Long departmentId;<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

Or<\/p>\n

\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n
5<\/div>\n
6<\/div>\n<\/td>\n
\n
\n
Class ClassRoom {<\/code><\/div>\n
    <\/code>Department department;<\/code><\/div>\n
}<\/code><\/div>\n
Class Department {<\/code><\/div>\n
    <\/code>Long id;<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

Then the big question is, what happens when we have following structure?

<\/div> <\/div><\/p>\n
\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n<\/td>\n
\n
\n
Class ClassRoom {<\/code><\/div>\n
    <\/code>Department department;<\/code><\/div>\n
    <\/code>Long departmentId;<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n
\n
\n\n\n\n
\n
1<\/div>\n
2<\/div>\n
3<\/div>\n
4<\/div>\n<\/td>\n
\n
\n
Class ClassRoom {<\/code><\/div>\n
    <\/code>Department department;<\/code><\/div>\n
    <\/code>Long departmentId;<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

How spring data resolves method name<\/h2>\n

Let\u2019s see how spring data jpa in spring boot decides what join should be used to avoid wrong select query.<\/p>\n

Consider the object structure as below for these classes : Student- classroom-department<\/p>\n

\n
\n\n\n\n
\n
01<\/div>\n
02<\/div>\n
03<\/div>\n
04<\/div>\n
05<\/div>\n
06<\/div>\n
07<\/div>\n
08<\/div>\n
09<\/div>\n
10<\/div>\n
11<\/div>\n
12<\/div>\n<\/td>\n
\n
\n
Class Student {<\/code><\/div>\n
    <\/code>...<\/code><\/div>\n
    <\/code>ClassRoom classRoom;<\/code><\/div>\n
}<\/code><\/div>\n
Class ClassRoom {<\/code><\/div>\n
    <\/code>\u2026..<\/code><\/div>\n
    <\/code>Department department;<\/code><\/div>\n
}<\/code><\/div>\n
Class Department{<\/code><\/div>\n
    <\/code>...<\/code><\/div>\n
    <\/code>Long id;<\/code><\/div>\n
}<\/code><\/div>\n<\/div>\n<\/td>\n<\/tr>\n<\/tbody>\n<\/table>\n<\/div>\n<\/div>\n

We will be using above database structure and try to understand what happens when we create a method findByClassRoomDepartmentId(Long id)<\/strong><\/p>\n

Following are the steps that spring data jpa will perform to create query<\/p>\n