I have 3 tables in a postgres data base and am using R2dbc to query and connect them in a relational manner.
I have 3 entity classes (possibly shouldn't be data classes, but shouldn't effect the example)
@Entity
@Table(name = "parent", schema = "public", catalog = "Test")
data class MyParentObject(
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Id
@org.springframework.data.annotation.Id
@Column(name = "id")
var id: Int = 0,
@Transient
var childData: List<MyChildObject>? = null
)
@Entity
@Table(name = "child", schema = "public", catalog = "Test")
data class MyChildObject(
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Id
@org.springframework.data.annotation.Id
@Column(name = "id")
var id: Int = 0,
@Column(name = "parent_id")
var parentId: Int? = null
@Transient
var grandchildData: List<MyGrandchildObject>? = null
)
@Entity
@Table(name = "grandchild", schema = "public", catalog = "Test")
data class MyGrandchildObject(
@GeneratedValue(strategy = GenerationType.IDENTITY)
@Id
@org.springframework.data.annotation.Id
@Column(name = "id")
var id: Int = 0
@Column(name = "child_id")
var childId: Int? = null
)
parent is one-to-many to child which is one-to-many of grandchild. parent_id and child_id act like fkeys.
I have a RestController which can return all Parent data populated with all child Data through these methods
fun viewAllParents(): Mono<MutableList<MyParentObject>> =
parentRepository.findAll()
.flatMap { Mono.just(it).addChildData(it.id) }
.collectList()
fun Mono<MyParentObject>.addChildData(id: Int): Mono<MyParentObject> =
this.zipWith(childRepository.getAllByParentIdEquals(id).collectList())
.map {
it.t1.childData = it.t2
it.t1
}
And I have another RestController that can return all ChildData with all Grandchild data (much the same as above) through these methods
fun viewAllChildren(): Mono<MutableList<MyChildObject>> =
childRepository.findAll()
.flatMap { Mono.just(it).addGrandchildData(it.id) }
.collectList()
fun Mono<MyChildObject>.addGrandchildData(id: Int): Mono<MyChildObject> =
this.zipWith(childOfChildRepository.getAllByChildIdEquals(id).collectList())
.map {
it.t1.childOfChildData = it.t2
it.t1
}
What I can't do and is my question, is how do I get viewAllParents() to also populate with Grandchild data. Do I need to convert var grandchildData: List<MyGrandchildObject> to a Flux and zip it with a new flux from the grandchildRepository? Or Am I looking at this the wrong way?
Any pointers would be much appreciated.
CodePudding user response：
I really liked the challenge of hierarchial data fetch using reactor. I don't know Kotlin but i have tried to reproduce the problem using java. I couldn't create a PostgreSQL table with the parent -> child -> grandChild hierarchy but i tried to simulate something similar via webclient( basically the logic would remain same). This is my code and this is what i tried to do and was able to get the result what you intended : https://github.com/harryalto/reactive-springwebflux
The crux of the solution is in the Handler code where i am using to build a sub flow based on list of childs and using that to tie together all
public Flux<Parent> getFamiliesHierarchy() { return getAllParents() .flatMap(parent -> getAllChildsList(parent.getId()) .flatMap(childList -> getChildsWithKids(childList)) .map(childList -> parent.toBuilder().children(childList).build() ) ); }
Below is the complete code
@Component
@Slf4j
public class FamilyHandler {
@Autowired
private WebClient webClient;
public Flux<Parent> getAllParents() {
return webClient
.get()
.uri("parents")
.retrieve()
.bodyToFlux(Parent.class);
}
public Mono<List<Child>> getAllChildsList(final Integer parentId) {
ParameterizedTypeReference<List<Child>> childList =
new ParameterizedTypeReference<List<Child>>() {};
return webClient
.get()
.uri("childs?parentId=" parentId)
.retrieve()
.bodyToMono(childList);
}
public Flux<GrandChild> getGrandKids(final Integer childId) {
return webClient
.get()
.uri("grandKids?childId=" childId)
.retrieve()
.bodyToFlux(GrandChild.class);
}
public Mono<List<GrandChild>> getGrandKidsList(final Integer childId) {
ParameterizedTypeReference<List<GrandChild>> grandKidsList =
new ParameterizedTypeReference<List<GrandChild>>() {};
return webClient
.get()
.uri("grandKids?childId=" childId)
.retrieve()
.bodyToMono(grandKidsList);
}
private Mono<List<Child>> getChildsWithKids(final List<Child> childList) {
return Flux.fromIterable(childList).flatMap(child ->
Mono.zip(Mono.just(child), getGrandKidsList(child.getId()))
.map(tuple2 -> tuple2.getT1().toBuilder().grandChildren(tuple2.getT2()).build())
).collectList();
}
public Flux<Parent> getFamiliesHierarchy() {
return getAllParents()
.flatMap(parent ->
getAllChildsList(parent.getId())
.flatMap(childList -> getChildsWithKids(childList))
.map(childList -> parent.toBuilder().children(childList).build()
)
);
}
}`
I used json-server for mocking the server
and below is my db.json file
{
"parents":[
{
"id": 1,
"name" : "Parent1",
"path":"1"
},
{
"id": 2,
"name" : "Parent2",
"path":"2"
}
],
"childs":[
{
"id": 1,
"parentId": 1,
"name": "child1Parent1",
"path":"1.1"
},
{
"id":2,
"parentId": 1,
"projectName": "child2Parent1",
"path":"1.2"
},
{
"id":3,
"parentId": 2,
"projectName": "child1Parent2",
"path":"2.1"
},
{
"id":4,
"parentId": 2,
"projectName": "child2Parent2",
"path":"2.2"
}
],
"grandKids":[
{
"id":1,
"childId": 2,
"projectName": "grandKid1child2Parent1",
"path":"1.2.1"
},
{
"id":3,
"childId": 2,
"projectName": "grandKid1child2Parent1",
"path":"1.2.2"
},
{
"id":2,
"childId": 4,
"projectName": "grandKid1child1Parent2",
"path":"2.2.1"
},
{
"id":4,
"childId": 4,
"projectName": "grandKid1child1Parent2",
"path":"2.2.2"
},
{
"id":5,
"childId": 3,
"projectName": "grandKid1child1Parent2",
"path":"2.1.1"
}
]
}
This is my controller code
@RestController
@Slf4j
public class FamilyController {
@Autowired
private FamilyHandler familyHandler;
@GetMapping(FAMILIES_ENDPOINT_V1)
public Flux<Parent> viewAllParents() {
return familyHandler.getFamiliesHierarchy();
}
}
We can easily retrofit the code for r2DBC repository.
-- UPDATE -- I was able to create the sample data and created an equivalent with R2DBC Here's the link to the gist