In mongodb version 3 using java api how do we give a hint while querying
The query result is FindIterable which has MongoCursor.
How should I give a hint to use a particular index.
With older versions there is DBCursor which have API's for hint.
modifiers should be used:
BasicDBObject index = new BasicDBObject("num", 1);
BasicDBObject hint = new BasicDBObject("$hint", index);
FindIterable<Document> iterable = collection.find().modifiers(hint);
You need to use FindIterable.modifiers method to specify $hint:
private static void testHint(MongoDatabase db) {
MongoCollection<Document> col = db.getCollection("Stores");
FindIterable<Document> iterable = col.find(new Document("store","storenumbervalue"));
iterable.modifiers(new Document("$hint","index_name"));
MongoCursor curs = iterable.iterator();
while(curs.hasNext()){
System.out.println(curs.next());
}
}
index_name - actual index name in mongo.
Related
I am trying to pass a hint on an aggregate in MongoDB Java Driver 3.6.3. The aggregate API allows for adding a hint as in:
MongoCollection<Document> coll = database.getCollection("myCollection")
ArrayList<BasicDBObject> docList = new ArrayList<BasicDBObject>();
BasicDBObject hint = new BasicDBObject("$hint","reportjob_customerId_1_siiDocumentAttributes.deleted_1");
MongoCursor<Document> cursor = coll.aggregate(docList).hint(hint).allowDiskUse(batchContext.isAllowDiskUse()).iterator();
I've tried with $hint and hint, but Mongo always returns Command failed with error -1: 'unrecognized field 'hint'
How do I properly send the hint on the aggregate call?
Looks like there is no support to pass the index name directly to hint. So you have pass the index creation document to the hint which you can get by name and use key to get the index document.
MongoCollection<Document> coll = database.getCollection("myCollection");
Bson index = coll.listIndexes().into(new ArrayList<>()).stream().filter(item -> item.getString("name").equals("reportjob_customerId_1_siiDocumentAttributes.deleted_1")).findFirst().get().getString("key");
List<BasicDBObject> docList = new ArrayList<BasicDBObject>();
MongoCursor<Document> cursor = coll.aggregate(docList).hint(index).allowDiskUse(batchContext.isAllowDiskUse()).iterator();
Legacy driver had support for both index name and document.
MongoClient client = new MongoClient();
DB database = client.getDB("myDatabase");
DBCollection coll = database.getCollection("myCollection");
List<BasicDBObject> docList = new ArrayList<BasicDBObject>();
AggregationOptions options = AggregationOptions.builder().allowDiskUse(batchContext.isAllowDiskUse()).build();
DBCursor dbCursor = ((DBCursor) coll.aggregate(docList, options)).hint("reportjob_customerId_1_siiDocumentAttributes.deleted_1");
You can create a jira to have the option to pass index name in the new driver here
I am migrating from the mongodb csharp driver 1.10.0 to 2.0.0.
One of the collection I am using is very big and has to fulfill many queries with different filter attributes. That is why I was relying on some index hint statements. With the v1.10 driver it looks like
myCollection.Find(query).SetHint("myIndexName");
I searched the v2 driver api but this hint method seems to be completly removed in the v2 driver. Is there an alternative? How should I do index hints with the v2 driver?
Note: The Solutions provided works for latest mongodb csharp drivers as well
You can use the FindOptions.Modifiers property.
var modifiers = new BsonDocument("$hint", "myIndexName");
await myCollection.Find(query, new FindOptions { Modifiers = modifiers }).ToListAsync();
May I ask why you are using the hint? Was the server consistently choosing the wrong index? You shouldn't need to do this except in exceptional cases.
Craig
Ideally, try to make the query in a way that mongodb optimizer can use the index automatically.
If you are using FindAsync then you will have a property named Hint. Use it like this:
If you have index named "myIndexName" which you want your query should use forcefully, then use like this:.
BsonString bsonString = new BsonString("myIndexName");
cursor = await collection.FindAsync(y => y.Population > 400000000,
new FindOptions<Person, Person>()
{
BatchSize = 200,
NoCursorTimeout = true,
AllowPartialResults = true,
Projection = "{'_id':1,'Name':1,'Population':1}"
Hint = bsonString.AsBsonValue,
}).ConfigureAwait(false);
You can fine BsonString class in MongoDB.Bson
With agregate you can force indice like this:
BsonString bsonString = new BsonString("ix_indice");
var query = this.collection.Aggregate(new AggregateOptions() { Hint = bsonString }).Match(new BsonDocument {..});
If you are using the Linq IQueryable, you can specify the hint (and other options) like this:
BsonDocument hint = new BsonDocument("myFieldName", 1);
// or
BsonDocument hint = new BsonString("myIndexName");
await collection.AsQueryable(new AggregateOptions { Hint = hint })
myFieldName can also reference a complex field, e.g. Metadata.FileName
myIndexName is the name of an index. I prefer to reference the field (first option) directly, instead of an index, for simple cases.
I have a list of documents with the structure:
{
from:"string"
to:"string"
payload:{
projectid:10000
}
}
I want to delete all documents with payload.projectid set to 10000 using the java API.
From the command-line I write:
db.notifications.find({"payload":{"projectid":10000}})
Error:
java.lang.RuntimeException: An operator that starts with $ is expected for projectid.
A similar error arises if I delete, whether through cli or programmatically.
This works in normal mongoDB.
How do I delete in db2 nosql?
Java code (for your reference!):
BasicDBObject query = new BasicDBObject();
query.append("to", "username");
query.append("from", "username2");
query.append("payload", new BasicDBObject().append("projectid", 10000));
System.out.println(query); // prints out okay
col.remove(query); //error
You should be using dot notation to reference the sub-document field:
Link
In your case it would be:
db.notifications.find({"payload.projectid":10000})
In Java the find should look something like this:
DBCollection notifications = db.getCollection("notifications")
DBObject subdocumentQuery = new BasicDBObject("payload.projectid", 10000);
DBCursor subdocumentCursor = notifications.find(subdocumentQuery);
I have accidentally deleted my index directory, now i am trying to rebuild all indexes.
I am using the hibernate search with JPA, lucene and MONGODB.
the following method is returning no results
public void rebuildIndex()throws Exception{
org.hibernate.search.jpa.FullTextEntityManager fem = org.hibernate.search.jpa.Search.getFullTextEntityManager(entityManager);
org.hibernate.search.query.dsl.QueryBuilder queryBuilder = fem.getSearchFactory().buildQueryBuilder().forEntity(Person.class).get();
org.apache.lucene.search.Query query = queryBuilder.all().createQuery();
FullTextQuery fullTextQuery = fem.createFullTextQuery(query, Person.class);
//fullTextQuery.initializeObjectsWith(ObjectLookupMethod.SKIP, DatabaseRetrievalMethod.FIND_BY_ID);
System.out.println(fullTextQuery.toString());
List<Person> results = fullTextQuery.getResultList();
fem.clear();
System.out.println(results.size());
for(Person p : results){
fem.index( p );
fem.flushToIndexes();
fem.clear();
}
//fem.createIndexer().startAndWait();
}
the method is returning no result. how should I get all data from mongoDb to rebuild index?
as hibernate search didn't work with criteria neither with JPQL and has his own JP-QL parser.
I couldn't create a findAll method to retrieve all objetcs
the only way was use a native mongoDb query:
org.hibernate.search.jpa.FullTextEntityManager fem = org.hibernate.search.jpa.Search.getFullTextEntityManager(entityManager);
Mongo mongo = new Mongo("127.0.0.1", 27017);
DB db = mongo.getDB("mainBase");
DBCollection dbCollection = db.getCollection("Persons");
DBCursor cursor = dbCollection.find();
Collection<String> ids = new ArrayList<String>();
String id = "";
while (cursor.hasNext()) {
id = cursor.next().get("_id").toString();
System.out.println(id);
ids.add(id);
}
System.out.println(">"+ids.size());
Person pes;
for(String p : ids){
pes = new Person();
pes.setId(p);
pes = find(pes);
System.out.println("indexing: "+pes.getId());
fem.index( pes );//index each element
fem.flushToIndexes();//apply changes to indexes
fem.clear();//free memory since the queue is processed
}
I am creating a collection in MongoDB in the following way and I want to create a 2dsphere index on location field of this collection from Java code. But I am not able to do so.
collection.ensureIndex() method expects a DBObject as a parameter but I cannot pass location to it.
How do I create collection.ensureIndex({"location" : "2dsphere"}) in Java code?
MongoDB allows me to do so in command prompt. But, I want to index it through code written in Java.
BasicDBObject doc = new BasicDBObject("attr1", nextLine[0])
.append("attr2", nextLine[1])
.append("edge-metro-code", nextLine[6])
.append("location", new BasicDBObject("type", "Point")
.append("coordinates",latLong))
.append("attr3", nextLine[9])
.append("attr4", nextLine[10])
ensureIndex() has been deprecated now. You should use createIndex() instead:
MongoClient mongoClient = new MongoClient();
DBCollection test = mongoClient.getDB("testdb").getCollection("test");
test.createIndex(new BasicDBObject("location","2dsphere"));
You should construct a new DBObject that represents your index. See the code bellow:
DBObject index2d = BasicDBObjectBuilder.start("location", "2dsphere").get();
DBCollection collection = new Mongo().getDB("yourdb").getCollection("yourcollection");
collection.ensureIndex(index2d);