Using Select in MongoDB
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