mobileNavlogo
headerlogo

Using Select in MongoDB

Blog Author

Tekslate

Published Date

19th September, 2018

Ratings

Views

676

  • Share this blog :

MongoDB is a cross-platform, document oriented database that provides, high performance, high availability, and easy scalability. MongoDB works on concept of collection and document.

MongoDB as-a-Service

private static void selectAllRecordsFromACollection(DBCollection collection) {
    DBCursor cursor = collection.find();
    while(cursor.hasNext()) {
        System.out.println(cursor.next());
    }
}
 
Output:
 
{ "_id" : { "$oid" : "538782753641d31b0cad0142"} , "employeeId" : 1 , "employeeName" : "TestEmployee_1"}
{ "_id" : { "$oid" : "538782753641d31b0cad0143"} , "employeeId" : 2 , "employeeName" : "TestEmployee_2"}
{ "_id" : { "$oid" : "538782753641d31b0cad0144"} , "employeeId" : 3 , "employeeName" : "TestEmployee_3"}
{ "_id" : { "$oid" : "538782753641d31b0cad0145"} , "employeeId" : 4 , "employeeName" : "TestEmployee_4"}
{ "_id" : { "$oid" : "538782753641d31b0cad0146"} , "employeeId" : 5 , "employeeName" : "TestEmployee_5"}
{ "_id" : { "$oid" : "538782753641d31b0cad0147"} , "employeeId" : 6 , "employeeName" : "TestEmployee_6"}
{ "_id" : { "$oid" : "538782753641d31b0cad0148"} , "employeeId" : 7 , "employeeName" : "TestEmployee_7"}
{ "_id" : { "$oid" : "538782753641d31b0cad0149"} , "employeeId" : 8 , "employeeName" : "TestEmployee_8"}
{ "_id" : { "$oid" : "538782753641d31b0cad014a"} , "employeeId" : 9 , "employeeName" : "TestEmployee_9"}
{ "_id" : { "$oid" : "538782753641d31b0cad014b"} , "employeeId" : 10 , "employeeName" : "TestEmployee_10"}

Select first document from a collection

private static void selectFirstRecordInCollection(DBCollection collection) {
    DBObject dbObject = collection.findOne();
    System.out.println(dbObject);
}
 
Output:
 
{ "_id" : { "$oid" : "538782a53641ed9125df86c0"} , "employeeId" : 1 , "employeeName" : "TestEmployee_1"}

Select single document and limited field(s) from a collection

private static void selectSingleRecordAndFieldByRecordNumber(DBCollection collection) {
    BasicDBObject whereQuery = new BasicDBObject();
    whereQuery.put("employeeId", 5);
    BasicDBObject fields = new BasicDBObject();
    fields.put("employeeId", 1);
 
    DBCursor cursor = collection.find(whereQuery, fields);
    while (cursor.hasNext()) {
        System.out.println(cursor.next());
    }
}
    
Output:
 
{ "_id" : { "$oid" : "53878332364101041fb2c141"} , "employeeId" : 5}

Select all documents with unique id from a collection

private static void selectAllRecordByRecordNumber(DBCollection collection) {
    BasicDBObject whereQuery = new BasicDBObject();
    whereQuery.put("employeeId", 5);
    DBCursor cursor = collection.find(whereQuery);
    while(cursor.hasNext()) {
        System.out.println(cursor.next());
    }
}
Output:
 
{ "_id" : { "$oid" : "538783623641e9b2da299fa7"} , "employeeId" : 5 , "employeeName" : "TestEmployee_5"}
 
Aspired to become an Mongo DB Training?
Explore the post to discover the know-hows on Mongo DB.

Document ids IN clause example

private static void in_Example(DBCollection collection) {
    BasicDBObject inQuery = new BasicDBObject();
    List<Integer> list = new ArrayList<Integer>();
    list.add(2);
    list.add(4);
    list.add(5);
    inQuery.put("employeeId", new BasicDBObject("$in", list));
    DBCursor cursor = collection.find(inQuery);
    while(cursor.hasNext()) {
        System.out.println(cursor.next());
    }
}
 
Output:
 
{ "_id" : { "$oid" : "5387838d3641024de174c795"} , "employeeId" : 2 , "employeeName" : "TestEmployee_2"}
{ "_id" : { "$oid" : "5387838d3641024de174c797"} , "employeeId" : 4 , "employeeName" : "TestEmployee_4"}
{ "_id" : { "$oid" : "5387838d3641024de174c798"} , "employeeId" : 5 , "employeeName" : "TestEmployee_5"}

Document ids less than or greater than clause example

private static void lessThan_GreaterThan_Example(DBCollection collection) {
    BasicDBObject getQuery = new BasicDBObject();
    getQuery.put("employeeId", new BasicDBObject("$gt", 2).append("$lt", 5));
    DBCursor cursor = collection.find(getQuery);
    while(cursor.hasNext()) {
        System.out.println(cursor.next());
    }
}
    
Output:
 
{ "_id" : { "$oid" : "538783b63641720cd34f98c8"} , "employeeId" : 3 , "employeeName" : "TestEmployee_3"}
{ "_id" : { "$oid" : "538783b63641720cd34f98c9"} , "employeeId" : 4 , "employeeName" : "TestEmployee_4"}

Document ids NOT IN clause example

private static void negation_Example(DBCollection collection) {
    BasicDBObject neQuery = new BasicDBObject();
    neQuery.put("employeeId", new BasicDBObject("$ne", 4));
    DBCursor cursor = collection.find(neQuery);
    while(cursor.hasNext()) {
        System.out.println(cursor.next());
    }
}
Output:
 
{ "_id" : { "$oid" : "538783db3641d3ca9d400510"} , "employeeId" : 1 , "employeeName" : "TestEmployee_1"}
{ "_id" : { "$oid" : "538783db3641d3ca9d400511"} , "employeeId" : 2 , "employeeName" : "TestEmployee_2"}
{ "_id" : { "$oid" : "538783db3641d3ca9d400512"} , "employeeId" : 3 , "employeeName" : "TestEmployee_3"}
{ "_id" : { "$oid" : "538783db3641d3ca9d400514"} , "employeeId" : 5 , "employeeName" : "TestEmployee_5"} //4 is missing
{ "_id" : { "$oid" : "538783db3641d3ca9d400515"} , "employeeId" : 6 , "employeeName" : "TestEmployee_6"}
{ "_id" : { "$oid" : "538783db3641d3ca9d400516"} , "employeeId" : 7 , "employeeName" : "TestEmployee_7"}
{ "_id" : { "$oid" : "538783db3641d3ca9d400517"} , "employeeId" : 8 , "employeeName" : "TestEmployee_8"}
{ "_id" : { "$oid" : "538783db3641d3ca9d400518"} , "employeeId" : 9 , "employeeName" : "TestEmployee_9"}
{ "_id" : { "$oid" : "538783db3641d3ca9d400519"} , "employeeId" : 10 , "employeeName" : "TestEmployee_10"}

Documents matching multiple fields example

private static void andLogicalComparison_Example(DBCollection collection) {
    BasicDBObject andQuery = new BasicDBObject();
    List<BasicDBObject> obj = new ArrayList<BasicDBObject>();
    obj.add(new BasicDBObject("employeeId", 2));
    obj.add(new BasicDBObject("employeeName", "TestEmployee_2"));
    andQuery.put("$and", obj);
 
    System.out.println(andQuery.toString());
 
    DBCursor cursor = collection.find(andQuery);
    while (cursor.hasNext()) {
        System.out.println(cursor.next());
    }
}
 
Output:
 
{ "$and" : [ { "employeeId" : 2} , { "employeeName" : "TestEmployee_2"}]}
{ "_id" : { "$oid" : "5387840336418a41167caaa4"} , "employeeId" : 2 , "employeeName" : "TestEmployee_2"}

Documents matching field value to some REGEX example

private static void regex_Example(DBCollection collection) {
    BasicDBObject regexQuery = new BasicDBObject();
    regexQuery.put("employeeName",
        new BasicDBObject("$regex", "TestEmployee_[3]")
        .append("$options", "i"));
 
    System.out.println(regexQuery.toString());
 
    DBCursor cursor = collection.find(regexQuery);
    while (cursor.hasNext()) {
        System.out.println(cursor.next());
    }
}
 
Output:
 
{ "employeeName" : { "$regex" : "TestEmployee_[3]" , "$options" : "i"}}
{ "_id" : { "$oid" : "538784213641917ce7068c57"} , "employeeId" : 3 , "employeeName" : "TestEmployee_3"}

Complete Code for all examples

package examples.mongodb.crud;
 
import java.net.UnknownHostException;
import java.util.ArrayList;
import java.util.List;
 
import com.mongodb.BasicDBObject;
import com.mongodb.DB;
import com.mongodb.DBCollection;
import com.mongodb.DBCursor;
import com.mongodb.DBObject;
import com.mongodb.MongoClient;
import com.mongodb.WriteResult;
 
public class MongoDBSelectExample {
    
    private static void setUpTestData(DBCollection collection){
        for (int i=1; i <= 10; i++) {
            collection.insert(new BasicDBObject().append("employeeId", i).append("employeeName", "TestEmployee_"+i));
        }
    }
    
    public static void main(String[] args) throws UnknownHostException
    {
        MongoClient mongo = new MongoClient("localhost", 27017);
        DB db = mongo.getDB("howtodoinjava");
        DBCollection collection = db.getCollection("users");
        
        //Delete All documents before running example again
        WriteResult result = collection.remove(new BasicDBObject());
        System.out.println(result.toString());
        
        //Set up test data
        setUpTestData(collection);
        
        //Select all document from a collection
        selectAllRecordsFromACollection(collection);
        
        //Select first document in collection
        selectFirstRecordInCollection(collection);
        
        //Select single document and single field based on record number
        selectSingleRecordAndFieldByRecordNumber(collection);
        
        //Select all documents where record number = n
        selectAllRecordByRecordNumber(collection);
        
        //In example
        in_Example(collection);
        
        //Less than OR greater than example
        lessThan_GreaterThan_Example(collection);
        
        //Select document where record number != n
        negation_Example(collection);
        
        //And logical comparison query example
        andLogicalComparison_Example(collection);
        
        //Select documents based on regex match LIKE example
        regex_Example(collection);
        
    }
 
    private static void selectFirstRecordInCollection(DBCollection collection) {
        DBObject dbObject = collection.findOne();
        System.out.println(dbObject);
    }
 
    private static void selectAllRecordsFromACollection(DBCollection collection) {
        DBCursor cursor = collection.find();
        while(cursor.hasNext()) {
            System.out.println(cursor.next());
        }
    }
 
    private static void selectSingleRecordAndFieldByRecordNumber(DBCollection collection) {
        BasicDBObject whereQuery = new BasicDBObject();
        whereQuery.put("employeeId", 5);
        BasicDBObject fields = new BasicDBObject();
        fields.put("employeeId", 1);
     
        DBCursor cursor = collection.find(whereQuery, fields);
        while (cursor.hasNext()) {
            System.out.println(cursor.next());
        }
    }
 
    private static void selectAllRecordByRecordNumber(DBCollection collection) {
        BasicDBObject whereQuery = new BasicDBObject();
        whereQuery.put("employeeId", 5);
        DBCursor cursor = collection.find(whereQuery);
        while(cursor.hasNext()) {
            System.out.println(cursor.next());
        }
    }
 
    private static void in_Example(DBCollection collection) {
        BasicDBObject inQuery = new BasicDBObject();
        List<Integer> list = new ArrayList<Integer>();
        list.add(2);
        list.add(4);
        list.add(5);
        inQuery.put("employeeId", new BasicDBObject("$in", list));
        DBCursor cursor = collection.find(inQuery);
        while(cursor.hasNext()) {
            System.out.println(cursor.next());
        }
    }
 
    private static void lessThan_GreaterThan_Example(
            DBCollection collection) {
        BasicDBObject gtQuery = new BasicDBObject();
        gtQuery.put("employeeId", new BasicDBObject("$gt", 2).append("$lt", 5));
        DBCursor cursor = collection.find(gtQuery);
        while(cursor.hasNext()) {
            System.out.println(cursor.next());
        }
    }
 
    private static void negation_Example(DBCollection collection) {
        BasicDBObject neQuery = new BasicDBObject();
        neQuery.put("employeeId", new BasicDBObject("$ne", 4));
        DBCursor cursor = collection.find(neQuery);
        while(cursor.hasNext()) {
            System.out.println(cursor.next());
        }
    }
 
    private static void andLogicalComparison_Example(DBCollection collection) {
        BasicDBObject andQuery = new BasicDBObject();
        List<BasicDBObject> obj = new ArrayList<BasicDBObject>();
        obj.add(new BasicDBObject("employeeId", 2));
        obj.add(new BasicDBObject("employeeName", "TestEmployee_2"));
        andQuery.put("$and", obj);
     
        System.out.println(andQuery.toString());
     
        DBCursor cursor = collection.find(andQuery);
        while (cursor.hasNext()) {
            System.out.println(cursor.next());
        }
    }
 
    private static void regex_Example(DBCollection collection) {
        BasicDBObject regexQuery = new BasicDBObject();
        regexQuery.put("employeeName",
            new BasicDBObject("$regex", "TestEmployee_[3]")
            .append("$options", "i"));
     
        System.out.println(regexQuery.toString());
     
        DBCursor cursor = collection.find(regexQuery);
        while (cursor.hasNext()) {
            System.out.println(cursor.next());
        }
    }
}
That’s all for different techniques to fetch data from MongoDB.

For indepth understanding click on

About Author
Authorlogo
Name

TekSlate

Author Bio

TekSlate is the best online training provider in delivering world-class IT skills to individuals and corporates from all parts of the globe. We are proven experts in accumulating every need of an IT skills upgrade aspirant and have delivered excellent services. We aim to bring you all the essentials to learn and master new technologies in the market with our articles, blogs, and videos. Build your career success with us, enhancing most in-demand skills .

Related Blogs

Write For Us