Query in arraylist by one element in spring boot h2

Question

I have a ClassRoom class, in my Spring Boot application. Here is what it looks like :

public class ClassRoom {

@Id @GeneratedValue Long classRoomID;

ArrayList<User>adminList=new ArrayList<>();
}

And in my ClassRoomRepository class, I have :

public interface ClassRoomRepository extends JpaRepository<ClassRoom,Long> {

@Query("select ClassRoom from ClassRoom c where c.adminList = ?1")
ArrayList<ClassRoom> findByAdminList(ArrayList<User> adminList);
/*
@Query("select ClassRoom from ClassRoom c where c. = ?1")
ArrayList<ClassRoom> findByAdmin(User admin);
*/
}

I can query to select ClassRoom where ArrayList of ClassRoom gets passed parameter.

But I want to query to select ClassRoom where I pass only one User as parameter and returns ArrayList of ClassRoom.(Commented section-nothing done so far)

If it is possible in this interface, how can I do so?

Amit Patil · Accepted Answer · 2019-08-31 08:18:54Z

1

Asuming you habe many-to-many association using join table, this is what you need,

 @Query(value = "SELECT DISTINCT cr FROM ClassRoom cr JOIN cr.admins a WHERE a = ?1")
 List<ClassRoom> findAllByAdmin(final Admin admin);

answered Aug 31, 2019 at 8:18

Amit Patil

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1 Comment

Maifee Ul Asad Over a year ago

can I have your mail or some contact, actually I need to discuss with you on this and this too.

Ken Chan · Accepted Answer · 2019-08-31 09:27:31Z

1

When mapping collection , Hibernate requires it to declare it using interface type such as List , Set , Map etc. But you are using ArrayList to declare the admin list , I am guessing the whole list will be stored to a single column with some binary data type in DB . No one would store the data in this funny way when using RDBMS unless you have strong reason to do it.

From what you describe , ClassRoom and User seem to be many to many. For demonstration convenience , I would map it as @ManyToMany:

@Entity
@Table
public class ClassRoom {

    @ManyToMany
    @JoinTable(name ="classroom_user",
             joinColumns = @JoinColumn(name = "classroom_id"),
            inverseJoinColumns = @JoinColumn(name = "user_id"))
    private List<User> admins = new ArrayList();
}

@Entity
@Table
public class User{

        @ManyToMany(mappedBy = "admins")
        private List<ClassRoom> classRooms  = Lists.newArrayList();
}

Then given an user admin ,to get all of his administrative class rooms :

@Query("select distinct cr from ClassRoom cr left join fetch cr.admins admin where admin = ?1 ")
public List<ClassRoom> findByAdmin(User admin);

Or :

@Query("select distinct cr from ClassRoom cr where ?1 member of cr.admins")
public List<ClassRoom> findByAdmin(User admin);

answered Aug 31, 2019 at 9:27

Ken Chan

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2 Comments

Maifee Ul Asad Over a year ago

In the User class, shouldn't it be @ManyToMany(mappedBy = "user") according to this , instead of admins

Ken Chan Over a year ago

Hi Maifee, No it should be the property name in the ClassRoom , so it is admins in my example .

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