Nested Group with Spring MongoDB - spring

Question

I need to generate a result with the number of alerts of each level for each user.
A structure similar to the following:
{
"identitity": "59e3b9dc5a3254691f327b67",
"alerts": [
{
"level": "INFO",
"count": "3"
},
{
"level": "ERROR",
"count": "10"
}
]
}
The alert entitity has the following structure:
#Document(collection = AlertEntity.COLLECTION_NAME)
public class AlertEntity {
public final static String COLLECTION_NAME = "alerts";
#Id
private ObjectId id;
#Field
private AlertLevelEnum level = AlertLevelEnum.INFO;
#Field("title")
private String title;
#Field("payload")
private String payload;
#Field("create_at")
private Date createAt = new Date();
#Field("delivered_at")
private Date deliveredAt;
#Field("delivery_mode")
private AlertDeliveryModeEnum deliveryMode =
AlertDeliveryModeEnum.PUSH_NOTIFICATION;
#Field("parent")
#DBRef
private ParentEntity parent;
#Field("son")
#DBRef
private SonEntity son;
private Boolean delivered = Boolean.FALSE;
}
I have implemented the following method tried to project the result in a nested way. But the "Identity" field is always null and the "alerts" field is a empty collection.
#Override
public List<AlertsBySonDTO> getAlertsBySon(List<String> sonIds) {
TypedAggregation<AlertEntity> alertsAggregation =
Aggregation.newAggregation(AlertEntity.class,
Aggregation.group("son.id", "level").count().as("count"),
Aggregation.project().and("son.id").as("id")
.and("alerts").nested(
bind("level", "level").and("count")));
// Aggregation.match(Criteria.where("_id").in(sonIds)
AggregationResults<AlertsBySonDTO> results = mongoTemplate.
aggregate(alertsAggregation, AlertsBySonDTO.class);
List<AlertsBySonDTO> alertsBySonResultsList = results.getMappedResults();
return alertsBySonResultsList;
}
The result I get is the following:
{
"response_code_name": "ALERTS_BY_SON",
"response_status": "SUCCESS",
"response_http_status": "OK",
"response_info_url": "http://yourAppUrlToDocumentedApiCodes.com/api/support/710",
"response_data": [
{
"identity": null,
"alerts": []
},
{
"identity": null,
"alerts": []
}
],
"response_code": 710
}
The result DTO is as follows:
public final class AlertsBySonDTO implements Serializable {
private static final long serialVersionUID = 1L;
#JsonProperty("identity")
private String id;
#JsonProperty("alerts")
private ArrayList<Map<String, String>> alerts;
public AlertsBySonDTO() {
super();
}
public AlertsBySonDTO(String id, ArrayList<Map<String, String>> alerts) {
super();
this.id = id;
this.alerts = alerts;
}
public String getId() {
return id;
}
public void setId(String id) {
this.id = id;
}
public ArrayList<Map<String, String>> getAlerts() {
return alerts;
}
public void setAlerts(ArrayList<Map<String, String>> alerts) {
this.alerts = alerts;
}
}
What needs to be done to project the result in a nested way?
Thanks in advance

Answer 1

In aggregation framework there is an $unwind operator which will basically transform your one element collection with nested array of two elements to two separate documents with one element from this array. So you'll get:
{
"identitity": "59e3b9dc5a3254691f327b67",
"alerts": {
"level": "INFO",
"count": "3"
}
}
{
"identitity": "59e3b9dc5a3254691f327b67",
"alerts": {
"level": "ERROR",
"count": "10"
}
}
And this is where you can start your group by with count. Should be working fine.