Learn to find documents in MongoDB. This mongodb find document tutorial covers a number of ways to query a single document or find multiple documents based on same condition as we do in SQL using WHERE CLAUSE.
Table of Contents 1) Select all documents from a collection 2) Select first document from a collection 3) Select single document and limited field(s) from a collection 4) Select all documents with unique id from a collection 5) Document ids IN clause example 6) Document ids less than or greater than clause example 7) Document ids NOT IN clause example 8) Documents matching multiple fields example 9) Documents matching field value to some REGEX example
MongoDB find document – test data preparation
For building and running examples used in this tutorial, I have populated 20 employee documents in database with employeeId from 1 to 20, and employeeName from TestEmployee_1 to TestEmployee_10.
private static void setUpTestData(DBCollection collection){
for (int i=1; i <= 10; i++) {
collection.insert(new BasicDBObject().append("employeeId", i).append("employeeName", "TestEmployee_"+i));
}
}
Now run our examples and fetch the data on different scenarios.
1. MongoDB find() – Select all documents from a collection
private static void selectAllRecordsFromACollection(DBCollection collection)
{
DBCursor cursor = collection.find();
while(cursor.hasNext())
{
System.out.println(cursor.next());
}
}
Program 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"}
2. MongoDB findOne() – Select first document from a collection
private static void selectFirstRecordInCollection(DBCollection collection)
{
DBObject dbObject = collection.findOne();
System.out.println(dbObject);
}
Program Output.
{ "_id" : { "$oid" : "538782a53641ed9125df86c0"} , "employeeId" : 1 , "employeeName" : "TestEmployee_1"}
3. MongoDB where clause – Select single document and limited field(s) from a collection
private static void selectSingleRecordAndFieldByRecordNumber(DBCollection collection)
{
BasicDBObject whereQuery = new BasicDBObject();
whereQuery.put("employeeId", 5);
BasicDBObject fields = new BasicDBObject();
fields.put("employeeId", 1);
DBCursor cursor = collection.find(whereQuery, fields);
while (cursor.hasNext()) {
System.out.println(cursor.next());
}
}
Program Output.
{ "_id" : { "$oid" : "53878332364101041fb2c141"} , "employeeId" : 5}
4. MongoDB find by document id
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());
}
}
Program Output.
{ "_id" : { "$oid" : "538783623641e9b2da299fa7"} , "employeeId" : 5 , "employeeName" : "TestEmployee_5"}
5. MongoDB IN clause example
private static void in_Example(DBCollection collection)
{
BasicDBObject inQuery = new BasicDBObject();
List<Integer> list = new ArrayList<Integer>();
list.add(2);
list.add(4);
list.add(5);
inQuery.put("employeeId", new BasicDBObject("$in", list));
DBCursor cursor = collection.find(inQuery);
while(cursor.hasNext()) {
System.out.println(cursor.next());
}
}
Program Output.
{ "_id" : { "$oid" : "5387838d3641024de174c795"} , "employeeId" : 2 , "employeeName" : "TestEmployee_2"}
{ "_id" : { "$oid" : "5387838d3641024de174c797"} , "employeeId" : 4 , "employeeName" : "TestEmployee_4"}
{ "_id" : { "$oid" : "5387838d3641024de174c798"} , "employeeId" : 5 , "employeeName" : "TestEmployee_5"}
6. MongoDB – Less than or greater than clause example
private static void lessThan_GreaterThan_Example(DBCollection collection)
{
BasicDBObject getQuery = new BasicDBObject();
getQuery.put("employeeId", new BasicDBObject("$gt", 2).append("$lt", 5));
DBCursor cursor = collection.find(getQuery);
while(cursor.hasNext()) {
System.out.println(cursor.next());
}
}
Program Output.
{ "_id" : { "$oid" : "538783b63641720cd34f98c8"} , "employeeId" : 3 , "employeeName" : "TestEmployee_3"}
{ "_id" : { "$oid" : "538783b63641720cd34f98c9"} , "employeeId" : 4 , "employeeName" : "TestEmployee_4"}
7. MongoDb NOT IN clause example
private static void negation_Example(DBCollection collection)
{
BasicDBObject neQuery = new BasicDBObject();
neQuery.put("employeeId", new BasicDBObject("$ne", 4));
DBCursor cursor = collection.find(neQuery);
while(cursor.hasNext()) {
System.out.println(cursor.next());
}
}
Program 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" : { "$oid" : "538783db3641d3ca9d400519"} , "employeeId" : 10 , "employeeName" : "TestEmployee_10"}
8. MongoDb find documents matching multiple fields example
private static void andLogicalComparison_Example(DBCollection collection)
{
BasicDBObject andQuery = new BasicDBObject();
List<BasicDBObject> obj = new ArrayList<BasicDBObject>();
obj.add(new BasicDBObject("employeeId", 2));
obj.add(new BasicDBObject("employeeName", "TestEmployee_2"));
andQuery.put("$and", obj);
System.out.println(andQuery.toString());
DBCursor cursor = collection.find(andQuery);
while (cursor.hasNext()) {
System.out.println(cursor.next());
}
}
Program Output.
{ "$and" : [ { "employeeId" : 2} , { "employeeName" : "TestEmployee_2"}]}
{ "_id" : { "$oid" : "5387840336418a41167caaa4"} , "employeeId" : 2 , "employeeName" : "TestEmployee_2"}
9. MongoDb find documents matching 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());
}
}
Program Output.
{ "employeeName" : { "$regex" : "TestEmployee_[3]" , "$options" : "i"}}
{ "_id" : { "$oid" : "538784213641917ce7068c57"} , "employeeId" : 3 , "employeeName" : "TestEmployee_3"}
10. All mondodb find query 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 ducument from MongoDB.
Happy Learning !!
References:
Leave a Reply