MongoDB Aggregation Pipeline – Count no of records that are matching a complex criteria – (Couldn’t find PersistentEntity for type java.lang.Object!)

I have documents with dynamic fields and I would need to find a count of matching records for a given complex query criteria

Example Entity

@Document(collection = "UserAttributes")
public class UserAttributesEntity {

    @Id
    @Getter
    private String id;

    @NotNull
    @Size(min = 1)
    @Getter @Setter
    private String userId;

    @NotNull
    @Getter @Setter
    private Map<String, Object> attributes = new HashMap<>();
}

Example Data:

{
    "_id" : ObjectId("6164542362affb14f3f2fef6"),
    "userId" : "89ee6942-289a-48c9-b0bb-210ea7c06a88",
    "attributes" : {
        "age" : 61,
        "name" : "Name1"
    }
},
{
    "_id" : ObjectId("6164548045cc4456792d5325"),
    "userId" : "538abb29-c09d-422e-97c1-df702dfb5930",
    "attributes" : {
        "age" : 40,
        "name" : "Name2",
        "location" : "IN"
    }
}

Expected Query Criteria:

"((userAttributes.name == 'Name1' && userAttributes.age > 40) OR (userAttributes.location  == 'IN'))

Building such complex Criteria using $match would be too much of implementation, so I was trying to use SPEL evolution through $project like below:

    private Mono<Long> aggregate() {
        final Aggregation aggregation = Aggregation
                .newAggregation(
                        Aggregation.project("userAttributes.playerLevel", "userAttributes.name")
                            .andExpression("((userAttributes.name == 'Name1' && userAttributes.age > 40) OR (userAttributes.location  == 'IN'))")
                            .as("result"),
                        Aggregation.match(Criteria.where("result").is(true)),
                        Aggregation.group().count().as("count"));

        return mongoTemplate.aggregate(aggregation, UserAttributesEntity.class, Map.class)
                .map(result -> Long.valueOf(result.get("count").toString()))
                .next();
    }

However, the above logic failing due to an exception:

org.springframework.data.mapping.MappingException: Couldn't find PersistentEntity for type java.lang.Object!
    at org.springframework.data.mapping.context.MappingContext.getRequiredPersistentEntity(MappingContext.java:119)
    at org.springframework.data.mapping.context.PersistentPropertyPathFactory.getPair(PersistentPropertyPathFactory.java:226)
    at org.springframework.data.mapping.context.PersistentPropertyPathFactory.createPersistentPropertyPath(PersistentPropertyPathFactory.java:199)
    at org.springframework.data.mapping.context.PersistentPropertyPathFactory.lambda$getPersistentPropertyPath$1(PersistentPropertyPathFactory.java:172)
    at java.base/java.util.concurrent.ConcurrentMap.computeIfAbsent(ConcurrentMap.java:330)
    at org.springframework.data.mapping.context.PersistentPropertyPathFactory.getPersistentPropertyPath(PersistentPropertyPathFactory.java:171)
    at org.springframework.data.mapping.context.PersistentPropertyPathFactory.from(PersistentPropertyPathFactory.java:71)
    at org.springframework.data.mapping.context.AbstractMappingContext.getPersistentPropertyPath(AbstractMappingContext.java:295)
    at org.springframework.data.mongodb.core.aggregation.TypeBasedAggregationOperationContext.getReferenceFor(TypeBasedAggregationOperationContext.java:163)
    at org.springframework.data.mongodb.core.aggregation.TypeBasedAggregationOperationContext.getReference(TypeBasedAggregationOperationContext.java:107)
    at org.springframework.data.mongodb.core.aggregation.AggregationExpressionTransformer$AggregationExpressionTransformationContext.getFieldReference(AggregationExpressionTransformer.java:82)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer$CompoundExpressionNodeConversion.convert(SpelExpressionTransformer.java:541)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer.transform(SpelExpressionTransformer.java:113)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer.transform(SpelExpressionTransformer.java:58)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer$ExpressionNodeConversion.transform(SpelExpressionTransformer.java:215)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer$ExpressionNodeConversion.transform(SpelExpressionTransformer.java:205)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer$OperatorNodeConversion.convert(SpelExpressionTransformer.java:257)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer.transform(SpelExpressionTransformer.java:113)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer.transform(SpelExpressionTransformer.java:58)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer$ExpressionNodeConversion.transform(SpelExpressionTransformer.java:215)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer$ExpressionNodeConversion.transform(SpelExpressionTransformer.java:205)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer$OperatorNodeConversion.convert(SpelExpressionTransformer.java:251)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer.transform(SpelExpressionTransformer.java:113)
    at org.springframework.data.mongodb.core.aggregation.SpelExpressionTransformer.transform(SpelExpressionTransformer.java:105)
    at org.springframework.data.mongodb.core.aggregation.ProjectionOperation$ExpressionProjectionOperationBuilder$ExpressionProjection.toMongoExpression(ProjectionOperation.java:438)
    at org.springframework.data.mongodb.core.aggregation.ProjectionOperation$ExpressionProjectionOperationBuilder$ExpressionProjection.toDocument(ProjectionOperation.java:433)
    at org.springframework.data.mongodb.core.aggregation.ProjectionOperation.toDocument(ProjectionOperation.java:261)
    at org.springframework.data.mongodb.core.aggregation.AggregationOperation.toPipelineStages(AggregationOperation.java:55)
    at org.springframework.data.mongodb.core.aggregation.AggregationOperationRenderer.toDocument(AggregationOperationRenderer.java:56)
    at org.springframework.data.mongodb.core.aggregation.AggregationPipeline.toDocuments(AggregationPipeline.java:81)
    at org.springframework.data.mongodb.core.aggregation.Aggregation.toPipeline(Aggregation.java:705)
    at org.springframework.data.mongodb.core.AggregationUtil.createPipeline(AggregationUtil.java:105)
    at org.springframework.data.mongodb.core.ReactiveMongoTemplate.aggregate(ReactiveMongoTemplate.java:1001)
    at org.springframework.data.mongodb.core.ReactiveMongoTemplate.aggregate(ReactiveMongoTemplate.java:970)

I tried digging in further, it seems to fail while its trying to map the fields used within the project to a proper entity object and in this case the projection fields here are actually are of Map object and its unable to identify the matching Entity (of-course the Map is within the UserAttributesEntity) – Is there a better way to solve my problem other than the above approach?

Answer

Using the raw aggregation resolved the issue:

return mongoTemplate.aggregate(aggregation, mongoTemplate.getCollectionName(UserAttributesEntity.class), Map.class)
    .map(result -> Long.valueOf(result.get("count").toString()))
    .next()