I have following codes:
mongoClient = new MongoClient( "localhost" , 27017 );
db = mongoClient.getDB("hcm");
DBCollection coll = db.getCollection("segment_cell_details");
BasicDBObject query = new BasicDBObject("cell_x", cell_x).append("cell_y", cell_y);
DBCursor cursor = coll.find(query);
Next, I want to add DBCursor in memcached :
c = new MemcachedClient(AddrUtil.getAddresses("localhost:11211"));
c.add("Key", 3600, cursor);
Then, System prints out "Non-serializable object error"
So, how can I add the result of query to memcached ?
The cursor is an iterator that lazily loads the results. You need to add the results not the iterator. I recommend adding them as serialised JSON.
while (cursor.hasNext())
c.add("key",3600,cursor.next().toString());
Related
I'm trying to follow this post to create a "contains" query in Java. The problem is it's giving me an error.
At the moment i have the following code:
MongoClient mongoClient = null;
DBCursor cursor = null;
mongoClient = new MongoClient( "localhost" , 27017 );
DB db = mongoClient.getDB("bd-films");
DBCollection coll = db.getCollection("films");
DBObject query = new BasicDBObject({"title" : {$regex : "name"}});
cursor = coll.find(query);
The error it gives me is in the 'query' line:
Syntax error on token ""title"", invalid Label
Syntax error, insert ";" to complete Statement
Syntax error on token ")", delete this token
I use the cursor for inserting it into a JTable.
Driver: mongo-java-driver-3.4.2
Thanks in advance.
Use new Document and MongoCollection api's for java driver 3.x version.
MongoClient mongoClient = new MongoClient("localhost", 27017);
MongoDatabase db = mongoClient.getDatabase("bd-films");
MongoCollection<Document> coll = db.getCollection("films");
List<Document> results = coll.find(Filters.regex("title", "name")).into(new ArrayList<>())
For accesssing MongoCursor,
FindIterable<Document> results = coll.find(Filters.regex("title", "name"));
MongoCursor<Document> cursor = results.iterator();
MongoClient mongo = new MongoClient();
DB db = mongo.getDB("mytest");
DBCollection col = db.getCollection("testt");
//read example
DBObject query = BasicDBObjectBuilder.start("$gte", "06/01/2016 00:00:00").add("$lte", "10/01/2016 00:00;00").get();
DBCursor cursor = col.find(query);
while(cursor.hasNext()) {
System.out.println("docc:");
System.out.println(cursor.next());
}
I am getting below exception while selecting data from MongoDB in Java.
com.mongodb.MongoQueryException: Query failed with error code 2 and
error message 'unknown top level operator: $gte' on server
127.0.0.1:27017 at com.mongodb.operation.FindOperation$1.call(FindOperation.java:493) at
com.mongodb.operation.FindOperation$1.call(FindOperation.java:483) at
com.mongodb.operation.OperationHelper.withConnectionSource(OperationHelper.java:241)
at
com.mongodb.operation.OperationHelper.withConnection(OperationHelper.java:214)
at
com.mongodb.operation.FindOperation.execute(FindOperation.java:483)
at com.mongodb.operation.FindOperation.execute(FindOperation.java:80)
at com.mongodb.Mongo.execute(Mongo.java:818) at
com.mongodb.Mongo$2.execute(Mongo.java:805) at
com.mongodb.DBCursor.initializeCursor(DBCursor.java:851) at
com.mongodb.DBCursor.hasNext(DBCursor.java:152) at
MongoFetch.main(MongoFetch.java:55)
Well you query does not mention the field you are querying on - just the range, therefore mongoDB does not really know what to do. Try something like that
...
BasicDBObject query = new BasicDBObject();
query.put("yourDateField", BasicDBObjectBuilder.start("$gte", fromDate).add("$lte", toDate).get());
DBCursor cursor = col.find(query);
...
I want to delete all documents in a collection in java. Here is my code:
MongoClient client = new MongoClient("10.0.2.113" , 27017);
MongoDatabase db = client.getDatabase("maindb");
db.getCollection("mainCollection").deleteMany(new Document());
Is this the correct way to do this?
I am using MongoDB 3.0.2
Using API >= 3.0:
MongoClient mongoClient = new MongoClient("127.0.0.1" , 27017);
MongoDatabase db = mongoClient.getDatabase("maindb");
db.getCollection("mainCollection").deleteMany(new Document());
To drop the collection (documents and indexes) you still can use:
db.getCollection("mainCollection").drop();
see https://docs.mongodb.org/getting-started/java/remove/#remove-all-documents
To remove all documents use the BasicDBObject or DBCursor as follows:
MongoClient client = new MongoClient("10.0.2.113" , 27017);
MongoDatabase db = client.getDatabase("maindb");
MongoCollection collection = db.getCollection("mainCollection")
BasicDBObject document = new BasicDBObject();
// Delete All documents from collection Using blank BasicDBObject
collection.deleteMany(document);
// Delete All documents from collection using DBCursor
DBCursor cursor = collection.find();
while (cursor.hasNext()) {
collection.remove(cursor.next());
}
If you want to remove all documents in collection then used below code :
db.getCollection("mainCollection").remove(new BasicDBObject());
Or If you want to drop whole collection then used this :
db.getCollection("mainCollection").drop();
For newer mongodb drivers you can use FindIterable to remove all documents in collection.
FindIterable<Document> findIterable = collection.find();
for (Document document : findIterable) {
collection.deleteMany(document);
}
I want to get ID by a matching name in mongoDB in Java.
That's my code:
MongoClient mongo = new MongoClient();
DB db = mongo.getDB("test");
DBCollection groupTable = db.getCollection("Items");
searchQuery.put("name", "John");
DBCursor cursor = groupTable.find(searchQuery);
while (cursor.hasNext()) {
System.out.println(cursor.next());
}
But it shows the whole row containt the name John, what I want is the ID not the whole thing.
{"list":[{"timestamp":{"$date":"2014-08-01T08:37:54.058Z"},"name":John,"_id":{"$oid":"53db5045ccf2b2399e0e6128"},"created":{"$date":"2014-08-}
Any help?
Thanks
It's very simple, just select the id...
while (cursor.hasNext()) {
System.out.println(cursor.next().get("_id"));
}
I am new to mongodb java api. I am trying to perform queries to my database. I ve read the database found the collections in it and I want to retrieve characteristics of users. My code:
ServerAddress serverAdr;
serverAdr = new ServerAddress(".. .. .., ...);
Twitter twitter = null;
MongoOptions options = new MongoOptions();
options.connectionsPerHost = 10;
MongoClient mongoClient = new MongoClient(.. ... ...", ...);
DB db = mongoClient.getDB("trendSetters");
System.out.println("Connect to database successfully");
//JSONObject content = getJSONFromFile("user.json");
Mongo mongo = null;
Set<String> colls = db.getCollectionNames();
mongo = new Mongo(serverAdr, options);
mongo.setWriteConcern(WriteConcern.SAFE);
DB db_se = mongo.getDB("iti_se");
DBCollection incollection = db_se.getCollection("cms_users_unique");
DBCollection outcollection = db_se.getCollection("cms_users_features");
for (String s : colls) {
System.out.println(s);
}
Now I want to perform queries to retrieve from all ids the usernames for example. How is it possible to do so in java mongodb API?
EDIT: What i ve tried
BasicDBObject query = new BasicDBObject();
DBCursor cursor;
query = new BasicDBObject("followers", new BasicDBObject("$gt", 1));
cursor = incollection.find(query);
while(cursor.hasNext()){
System.out.println(cursor.next());
}
However, it doesnot return nothing.
You asked: "I want to perform queries to retrieve from all ids the usernames for example."
To retrieve all documents from collection you can use find() method of the DBCollection.
DBCursor cursor;
cursor = incollection.find();
After that, you can get the field value by its name for each document as below
while(cursor.hasNext()){
System.out.println(cursor.next().get("username"));
}
If you need to add more criterias to query documents:
BasicDBObject query1;
DBCursor cursor;
query1 = new BasicDBObject("age", new BasicDBObject("$gt", 25));
cursor = incollection.find(query1);
while(cursor.hasNext()){
System.out.println(cursor.next().get("username"));
}
DBCollections objects have method find which takes mainly a DBObject argument. For instance, if you want to find users with age > 50 this can help you.
query = new BasicDBObject("age", new BasicDBObject("$gt", 50));
cursor = incollection.find(query);
while(cursor.hasNext()){
System.out.println(cursor.next());
}
BasicDBObject take first argument, that is a field, and second argument that is another BasicDBObject or a value. With composition of these objects you can build any query.
I recommend you take a look at MongoDB Documentation, it's pretty good.
Mongo Java Driver http://docs.mongodb.org/ecosystem/drivers/java/
See Javadoc. http://api.mongodb.org/java/current/