To establish a one-to-one relationship through a linking table using Kotlin and exposed, you can follow these steps:
data class User(
val id: Int,
val name: String,
...
)
data class Profile(
val id: Int,
val bio: String,
...
)
Table
class and add two foreign key columns, one for User and another for Profile.object UserProfiles: Table() {
val userId = integer("userId").references(Users.id)
val profileId = integer("profileId").references(Profiles.id)
}
class UserDao {
fun getUserById(id: Int): User = ...
fun saveUser(user: User): User = ...
}
class ProfileDao {
fun getProfileById(id: Int): Profile = ...
fun saveProfile(profile: Profile): Profile = ...
}
join()
function to define a mapping between the User and Profile entities using the linking table. This will allow you to easily retrieve the linked entity from either side of the relationship.val userToProfile = UserProfiles.join(Users, JoinType.INNER, UserProfiles.userId, Users.id).join(
Profiles,
JoinType.INNER,
UserProfiles.profileId,
Profiles.id
)
val profileToUser = UserProfiles.join(Profiles, JoinType.INNER, UserProfiles.profileId, Profiles.id).join(
Users,
JoinType.INNER,
UserProfiles.userId,
Users.id
)
val user = userDao.getUserById(userId)
val profile = userToProfile.select { Users.id eq userId }.map { it[Profiles] }.single()
This will retrieve the user from the database, then use the userToProfile
mapping to retrieve the profile of that user. Similarly, you can retrieve the user of a profile using the profileToUser
mapping.
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Asked: 2021-07-03 11:00:00 +0000
Seen: 12 times
Last updated: May 10 '21