Develop Reference

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);
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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/

Returning certain amount of documents from elasticsearch query in java

I am trying to limit the document size returned by my query.i want lets say 10 documents back only,any my query normally displays 22,how would i go buy setting a limit for the returned output. i am aware i can just limit the list size by creating a list and adding to that list however i want to do it on the query level.
My Query: Thanks in advance :)
ueryBuilder raceGenderQuery = QueryBuilders.boolQuery()
.must(termQuery("lep_etg_desc", "indian"))
.must(termQuery("lep_gen_desc", "male"));
Set<String> suburbanLocationSet = new HashSet<String>();
suburbanLocationSet.add("queensburgh");
suburbanLocationSet.add("umhlanga");
suburbanLocationSet.add("tongaat");
suburbanLocationSet.add("phoenix");
suburbanLocationSet.add("shallcross");
suburbanLocationSet.add("balito");
//Build the necessary location query.
QueryBuilder locationQuery = QueryBuilders.boolQuery().must(termsQuery("lep_suburb_home", suburbanLocationSet));
//Combine all Queries so that its filtered to get exact results.
FilteredQueryBuilder finalSearchQuery = QueryBuilders.filteredQuery(QueryBuilders.boolQuery().must(raceGenderQuery).must(locationQuery), FilterBuilders.boolFilter().must(FilterBuilders.rangeFilter("lep_age").gte(25).lte(45)).must(FilterBuilders.rangeFilter("lep_max_income").gte(25000).lte(45000)));
//Run Query through elasticsearch iterating through documents in the traceps index for query matches.
List<Leads> finalLeadsList = new ArrayList<Leads>();
for (Leads leads : this.leadsRepository.search(finalSearchQuery)) {
finalLeadsList.add(leads);
}

I think this is what you want:
SearchResponse response = client.prepareSearch().setSearchType(SearchType.QUERY_THEN_FETCH).setSize(10).setQuery(finalSearchQuery).execute().get
You have to use QUERY_THEN_FETCH for it to return exactly size results because otherwise it gets size results from each shard.

Hibernate search : single search term with space

I am a newbie to hibernate search.
I am trying to implement a engine in which the results are exact matches.
My persistence class changes
#Field(index=Index.UN_TOKENIZED, store=Store.NO)
private String offerTitle;
Implementation changes
String[] offerFields = new String[] { "offerTitle"};
MultiFieldQueryParser parser = new MultiFieldQueryParser(Version.LUCENE_31,offerFields,new KeywordAnalyzer());
org.apache.lucene.search.Query query = parser.parse(queryString);
org.hibernate.Query offerHibQuery = fullTextSession.createFullTextQuery(query, Offer.class);
List<?> offerResults = offerHibQuery.list();
It works fine until the search term has space in it. When search term contains space, it gets no results.
For example: For the search term: "Comcast offer name" I get no results, and the query is broken into offerTitle:Comcast offerTitle:offer offerTitle:name
Is there any way to search for exact match with spaces?
I tried this:
QueryBuilder queryBuilder_1 = fullTextSession.getSearchFactory().buildQueryBuilder().forEntity(Offer.class).get();
org.apache.lucene.search.Query offerCode_1 = queryBuilder_1.phrase().onField("offerTitle").sentence(queryString).createQuery();
org.hibernate.Query offerCodeHibQuery = fullTextSession.createFullTextQuery(offerCode_1);
List<?> offerCodeResults = offerCodeHibQuery.list();
It is still not working.

You are not tokenizing the field, so you need to search with a single, unanalyzed term. The simplest way to do that, I find, is to go straight to the Lucene APIs and just construct a TermQuery, like:
Query query = new TermQuery(new Term("offerTitle", queryString));
I think this should also work:
queryBuilder_1.keyword().onField("offerTitle").matching(queryString).createQuery();

queryBuilder_1.phrase().withSlop(0)
.onField("offerTitle").sentence(queryString).createQuery()

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?