Java Mongodb 3.x ~ Specific document key's with value and

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N.S.KARTHIK

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Jul 24, 2017, 12:51:44 AM7/24/17

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Spec : Jdk 1.7,Mongodb 3.0.12,Win-10

I have gone thru all of the Mongo's docs : http://mongodb.github.io/mongo-java-driver/3.4/driver/tutorials/

I have done some samples suggested by Professionals on Filter & projections.

Question I am still not able to achieve the following equivalence of an SQL query in MongoDB's NO-SQL

"Select cola, colb, colc, cold from Table web-services where cola='1000' and colb='DAO' and group by colc"

I need a simple example in Mongodb 3.x API to have Filters with Projections for the values passed to keys in the SQL query above.

with regards
Karthik

Wan Bachtiar

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Jul 31, 2017, 4:05:15 AM7/31/17

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I need a simple example in Mongodb 3.x API to have Filters with Projections for the values passed to keys in the SQL query above.

Hi Karthik,

I would recommend to first try out MongoDB Aggregation Pipeline via mongo shell before attempting to apply it using a driver.
The equivalent of the above SQL in mongo shell would be:

db.collectionName.aggregate([
    {$match:{cola:"1000", colb:"DAO"}}, 
    {$group:{"_id":"$colc", cola:{$first:"$cola"}, colb:{$first:"$colb"}, cold:{$first:"$cold"}}}, 
    {$project:{_id:0, cola:"$cola", colb:"$colb", colc:"$_id", cold:"$cold"}}
]);

Note that above I’m utilising $first group accumulator above for cola, colb and cold. Please see Group Accumulator Operators for other aggregation operations.

Using MongoDB Java driver, the equivalent aggregation pipeline above is as below:

MongoDatabase db = mongoClient.getDatabase("dbName");

Document match = Document.parse("{$match:{cola:'1000', colb:'DAO'}}");
Document group = Document.parse("{$group:{'_id':'$colc', cola:{$first:'$cola'}, colb:{$first:'$colb'}, cold:{$first:'$cold'}}}"); 
Document project = Document.parse("{$project:{cola:'$cola', colb:'$colb', colc:'$_id', cold:'$cold', _id:0}}");

List<Document> pipeline = asList(match, group, project);

AggregateIterable<Document> iterable = db.getCollection("collectionName").aggregate(pipeline);