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Association API
Overview
The Association API makes it easy to navigate association objects from the EntityStore obtained by executing a query specifying include or includeAll.
Annotating an entity class (or entity definition class) with a dedicated annotation generates a utility function for navigating association objects.
Note
Sets returned by the Association API preserve the order of elements.Note
The Association API is an experimental feature. To use it, add the following code to your Gradle build script:
tasks {
withType<org.jetbrains.kotlin.gradle.tasks.KotlinCompile>().configureEach {
kotlinOptions.freeCompilerArgs += listOf("-opt-in=org.komapper.annotation.KomapperExperimentalAssociation")
}
}
Annotations
@KomapperOneToOne
Indicates a one-to-one relationship between the annotated entity class and the target entity class.
@KomapperEntity
@KomapperOneToOne(targetEntity = Address::class)
data class Employee(...)
The targetEntity property specifies the entity class (or entity definition class) associated with the annotated class.
The specification is required.
The navigator property specifies the name of a utility function for navigating the association.
If not specified, it is inferred from the value specified for the targetEntity property.
The following utility function is generated from the above definition:
fun example.Employee.`address`(
store: org.komapper.core.dsl.query.EntityStore,
source: example._Employee = org.komapper.core.dsl.Meta.`employee`,
target: example._Address = org.komapper.core.dsl.Meta.`address`,
): example.Address? {
return store.oneToOne(source, target)[this]
}
@KomapperManyToOne
Indicates a many-to-one relationship between the annotated entity class and the target entity class.
@KomapperEntity
@KomapperManyToOne(targetEntity = Department::class)
data class Employee(...)
The targetEntity property specifies the entity class (or entity definition class) associated with the annotated class.
The specification is required.
The navigator property specifies the name of a utility function for navigating the association.
If not specified, it is inferred from the value specified for the targetEntity property.
The following utility function is generated from the above definition:
fun example.Employee.`department`(
store: org.komapper.core.dsl.query.EntityStore,
source: example._Employee = org.komapper.core.dsl.Meta.`employee`,
target: example._Department = org.komapper.core.dsl.Meta.`department`,
): example.Department? {
return store.manyToOne(source, target)[this]
}
@KomapperOneToMany
Indicates a one-to-many relationship between the annotated entity class and the target entity class.
@KomapperEntity
@KomapperOneToMany(targetEntity = Employee::class, navigator = "employees")
data class Department(...)
The targetEntity property specifies the entity class (or entity definition class) associated with the annotated class.
The specification is required.
The navigator property specifies the name of a utility function for navigating the association.
If not specified, it is inferred from the value specified for the targetEntity property.
The following utility function is generated from the above definition:
fun example.Department.`employees`(
store: org.komapper.core.dsl.query.EntityStore,
source: example._Department = org.komapper.core.dsl.Meta.`department`,
target: example._Employee = org.komapper.core.dsl.Meta.`employee`,
): Set<example.Employee> {
return store.oneToMany(source, target)[this] ?: emptySet()
}
@KomapperLink
Indicates the associated source entity metamodel and the associated target entity metamodel.
It can be specified in the link property of the following annotations:
@KomapperOneToOne@KomapperManyToOne@KomapperOneToMany
@KomapperAggregateRoot
Indicates that the annotated entity class (or entity definition class) is the aggregate root.
@KomapperEntity
@KomapperAggregateRoot(navigator = "departments")
data class Department(...)
The navigator property specifies the name of a utility function to retrieve the aggregate root.
If not specified, it is inferred from the annotated class.
The above definition generates the following utility function:
fun org.komapper.core.dsl.query.EntityStore.`departments`(
target: example._Department = org.komapper.core.dsl.Meta.`department`,
): Set<example.Department> {
return this[target]
}
Example
Entity class definitions
Suppose we have the following entity class definitions:
@KomapperEntity
@KomapperOneToOne(targetEntity = Employee::class)
data class Address(
@KomapperId
val addressId: Int,
val street: String,
)
@KomapperEntity
@KomapperAggregateRoot("departments")
@KomapperOneToMany(targetEntity = Employee::class, navigator = "employees")
data class Department(
@KomapperId
val departmentId: Int,
val departmentName: String,
)
@KomapperEntity
@KomapperManyToOne(targetEntity = Department::class)
@KomapperOneToOne(targetEntity = Address::class)
data class Employee(
@KomapperId
val employeeId: Int,
val employeeName: String,
val departmentId: Int,
val addressId: Int,
)
Navigation code
We can concisely retrieve the association objects from the EntityStore by using the generated utility functions:
val a = Meta.address
val e = Meta.employee
val d = Meta.department
val query = QueryDsl.from(a)
.innerJoin(e) {
a.addressId eq e.addressId
}.innerJoin(d) {
e.departmentId eq d.departmentId
}.includeAll()
val store: EntityStore = db.runQuery(query)
for (department in store.departments()) {
val employees = department.employees(store)
for (employee in employees) {
val address = employee.address(store)
println("department=${department.departmentName}, employee=${employee.employeeName}, address=${address?.street}")
}
}
Navigation code using context receiver
Enabling the komapper.enableEntityStoreContext
option allows more concise navigation of association objects
by eliminating the need to pass EntityStore arguments explicitly.
val a = Meta.address
val e = Meta.employee
val d = Meta.department
val query = QueryDsl.from(a)
.innerJoin(e) {
a.addressId eq e.addressId
}.innerJoin(d) {
e.departmentId eq d.departmentId
}.includeAll()
val store: EntityStore = db.runQuery(query)
with(store.asContext()) {
for (department in departments()) {
val employees = department.employees()
for (employee in employees) {
val address = employee.address()
println("department=${department.departmentName}, employee=${employee.employeeName}, address=${address?.street}")
}
}
}