Develop Reference

MongoTemplate : group by on multiple fields with max operator

Want to convert following query to Java Mongo template aggregation but don't know how to write multiple fields in group operator with max operator condition.
db.getCollection('mycollection').aggregate([
{
$group: {
_id: "$somefield.$id",
xyz: {
"$max": "$_id"
}
}
}
])
tried to find on mongodb forums, and other website but no solution.

Simply use:
Aggregation.group("somefield.id").max("_id").as("xyz");
And you can get the data with something like this:
// Create aggregation step
AggregateOperation groupOperation = Aggregation.group("somefield.id").max("_id").as("xyz");
// Create aggregation object
Aggregation aggregation = Aggregation.newAggregation(groupOperation);
// Run the aggregate query
AggregationResults<YourClass> result = mongoTemplate.aggregate(aggregation, "mycollection", YourClass.class);
// Get result as list
List<YourClass> listResult = result.getMappedResults();

How to do pagination with DynamoDBMapper?

I'm developing an application in Quarkus that integrates with the DynamoDB database. I have a query method that returns a list and I'd like this list to be paginated, but it would have to be done manually by passing the parameters.
I chose to use DynamoDBMapper because it gives more possibilities to work with lists of objects and the level of complexity is lower.
Does anyone have any idea how to do this pagination manually in the function?

DynamoDBScanExpression scanExpression = new DynamoDBScanExpression()
.withLimit(pageSize)
.withExclusiveStartKey(paginationToken);
PaginatedScanList<YourModel> result = mapper.scan(YourModel.class, scanExpression);
String nextPaginationToken = result.getLastEvaluatedKey();
You can pass the pageSize and paginationToken as parameters to your query method. The nextPaginationToken can be returned along with the results, to be used for the next page.

DynamoDB Mapper paginates by iterating over the results, by lazily loading the dataset:
By default, the scan method returns a "lazy-loaded" collection. It initially returns only one page of results, and then makes a service call for the next page if needed. To obtain all the matching items, iterate over the result collection.
Ref
For example:
List<Customer> result = mapper.scan(Customer.class, scanExpression);
for ( Customer cust : result ) {
System.out.println(cust.getId());
}
To Scan manually page by page you can use ScanPage
final DynamoDBScanExpression scanPageExpression = new DynamoDBScanExpression()
.withLimit(limit);
do {
ScanResultPage<MyClass> scanPage = mapper.scanPage(MyClass.class, scanPageExpression);
scanPage.getResults().forEach(System.out::println);
System.out.println("LastEvaluatedKey=" + scanPage.getLastEvaluatedKey());
scanPageExpression.setExclusiveStartKey(scanPage.getLastEvaluatedKey());
} while (scanPageExpression.getExclusiveStartKey() != null);
Ref
Ref

Spring data mongodb - empty result while trying aggregate and project

I am having a bit of trouble with projecting and paging with mongooperations. I always get empty result. The query criteria working fine without aggregation. I tryed the same code without paging(skip&limit) and without sort but I still get the empty result.
My code:
public List<ProfileBasic> findAllActiveUsersByGenderAndAgeBetweenProjectedPage(Gender gender, int fromAge, int toAge, int pageSize, int page) {
Criteria criteria = Criteria.where("gender").is(gender).and("confirmed").is(true)
.and("dateOfBirth").lte(LocalDate.now().minusYears(fromAge))
.gte(LocalDate.now().minusYears(toAge));
MatchOperation match = Aggregation.match(criteria);
ProjectionOperation project = Aggregation.project()
.and("id").as("id")
.and("name").as("name")
.and("lastName").as("lastName")
.and("gender").as("gender")
.and("dateOfBirth").as("dateOfBirth")
.and("lastVisit").as("lastVisit");
SkipOperation skip = new SkipOperation(pageSize*(page-1));
LimitOperation limit = new LimitOperation(pageSize);
SortOperation sort = new SortOperation(new Sort(Sort.Direction.DESC, "lastVisit"));
Aggregation aggregate = Aggregation.newAggregation(project, match, skip, limit, sort);
return operations.aggregate(aggregate, User.class, ProfileBasic.class).getMappedResults();
}
I would appreciate any help.

When we do Aggregation in MongoDB data is processed in stages and the output of one stage is provided as input to the next stage.
In my code first stage was project and not match(query):
Aggregation aggregate = Aggregation.newAggregation(project, match, skip, limit, sort);
Thats why it didn't work.
I changed it to:
Aggregation aggregate = Aggregation.newAggregation(match, skip, limit, project, sort);
And now it works fine.

Mongo spring query where two fields are equal

I want to execute a query in java where path and _id are two fields of the mongo document.
I want to get results list where these two fields are equal in the document.
I have tried using the following query.But could not retrieve the results properly.Received empty list which is not the case.
List<Metadata> MetadataList= ops.find(new Query(Criteria.where("path").is("_id")), Metadata.class);
How to get results where two field values are equal in mongo.

What you are looking for is the $where operator in MongoDB. Standard query operations do not compare the values of one field against another. In order to do this, you need to employ the JavaScript evaluation server side which can actually compare the two field values:
BasicQuery query = new BasicQuery(
new BasicDBObject("$where", "return this._id == this.path")
);
<Metadata> MetadataList = ops.find(query, Metadata.class);
Or you can do the same thing with native operators through the $redact pipeline stage available to the aggregation framework.
Pretty sure there is no $redact support in spring mongo as yet, but you can wrap the aggregation operation with a class to do so:
public class CustomAggregationOperation implements AggregationOperation {
private DBObject operation;
public CustomAggregattionOperation (DBObject operation) {
this.operation = operation;
}
#Override
public DBObject toDBObject(AggregationOperationContext context) {
return context.getMappedObject(operation);
}
}
And use it like this:
Aggregation aggregation = newAggregation(
new CustomAggregationOperation(
new BasicDBObject(
"$redact",
new BasicDBObject("$cond",
new BasicDBObject()
.append("if", new BasicDBObject(
"$eq", Arrays.asList("$_id", "$path")
))
.append("then", "$$KEEP")
.append("else", "$$PRUNE")
)
)
)
);
AggregationResults<Metadata> results = ops.aggregate(
(TypedAggregation<Metadata>) aggregation, Metadata.class);
So basic MongoDB query operations do not compare field values against each other. To do this you need to follow one of the methods here.

You can use BasicDBObject to add condition.
Try something
BasicDBObject query = new BasicDBObject("path", new BasicDBObject("$eq", "_id");
collection.find(query);
Please refer the below link for more information
http://mongodb.github.io/mongo-java-driver/2.13/getting-started/quick-tour/

QueryDSL & Hibernate-Search with Lucene Analyzers

I configured Hibernate-Search to use my custom analyzer when indexing my entities. However when I try and search with QueryDSL's Hibernate-Search integration, it doesn't find entities, but if I use straight hibernate-search it finds something.
#AnalyzerDef(name = "customanalyzer",
tokenizer = #TokenizerDef(factory = StandardTokenizerFactory.class),
filters = {
#TokenFilterDef(factory = LowerCaseFilterFactory.class),
#TokenFilterDef(factory = SnowballPorterFilterFactory.class, params = {
#Parameter(name = "language", value = "English")
})
})
#Analyzer(definition = "customanalyzer")
public abstract class Post extends BaseEntity {}
I indexed an entity with a title of "the quick brown fox jumped over the lazy dog".
These work…
List articlePosts = fullTextEntityManager.createFullTextQuery(queryBuilder.keyword().onFields("title").matching("jumped").createQuery(), ArticlePost.class).getResultList(); // list of 2
List articlePosts = fullTextSession.createFullTextQuery(queryBuilder.keyword().onFields("title").matching("jumped").createQuery(), ArticlePost.class).getResultList(); // list of 2
This does not…
SearchQuery<ArticlePost> query = new SearchQuery<ArticlePost>(this.entityManagerFactory.createEntityManager().unwrap(HibernateEntityManager.class).getSession(), post);
List articlePosts = query.where(post.title.contains("jumped")).list() // empty list
But a search with how it is likely stored in Lucene (probable result of SnowballPorter), then it works…
SearchQuery<ArticlePost> query = new SearchQuery<ArticlePost>(this.entityManagerFactory.createEntityManager().unwrap(HibernateEntityManager.class).getSession(), post);
List articlePosts = query.where(post.title.contains("jump")).list() // list of 2
So it seems like when using QueryDSL, that the analyzer isn't being run before it does the query. Can anyone confirm this is the problem, and is there anyway to have them automatically run before QueryDSL runs the query?

Regarding your question, the analyzer is applied per default when using the query DSL. In most cases it makes sense to use the same analyzer for indexing and searching. For this reason the analyzer is applied per default unless 'ignoreAnalyzer' is used.
Why your second example does not work I cannot tell you. SearchQuery is not part of the Hibernate Search or ORM API. It must be an internal class of your application. What's happening in this class? Which type of query is it using?