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Start at both ends
In MongoDB we use the find and findOne methods to find data in a collection.
statement is used to find data in a table in a MySQL database.
To select data from a collection in MongoDB, we can use the findOne() method.
method returns the first occurrence in the selection.
method is a query object. In this example we use an empty query object, which selects all documents in a collection (but returns only the first document).
Find the first document in the customers collection:
let MongoClient = require('mongodb').MongoClient;
let url = "mongodb://localhost:27017/";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
let dbo = db.db("mydb");
dbo.collection("customers").findOne({}, function(err, result) {
if (err) throw err;
console.log(result.name);
db.close();
});
});
Save the code above in a file called "demo_mongodb_findone.js" and run the file:
Run "demo_mongodb_findone.js"C:\Users\
>node demo_mongodb_findone.js Which will give you this result: Company Inc.
To select data from a table in MongoDB, we can also use the find() method.
method returns all occurrences in the selection.
method is a query object. In this example we use an empty query object, which selects all documents in the collection. No parameters in the find() method gives you the same result as
SELECT *in MySQL.
Find all documents in the customers collection:
let MongoClient = require('mongodb').MongoClient;
let url = "mongodb://localhost:27017/";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
let dbo = db.db("mydb");
dbo.collection("customers").find({}).toArray(function(err, result) {
if (err) throw err;
console.log(result);
db.close();
});
});
Save the code above in a file called "demo_mongodb_find.js" and run the file:
Run "demo_mongodb_find.js"C:\Users\
>node demo_mongodb_find.js Which will give you this result: [
{ _id:
58fdbf5c0ef8a50b4cdd9a84 , name: 'John', address: 'Highway 71'},
{ _id:
58fdbf5c0ef8a50b4cdd9a85 , name: 'Peter', address: 'Lowstreet 4'},
{
_id: 58fdbf5c0ef8a50b4cdd9a86 , name: 'Amy', address: 'Apple st 652'},
{ _id: 58fdbf5c0ef8a50b4cdd9a87 , name: 'Hannah', address:
'Mountain 21'},
{ _id: 58fdbf5c0ef8a50b4cdd9a88 , name: 'Michael', address: 'Valley 345'},
{ _id: 58fdbf5c0ef8a50b4cdd9a89 , name: 'Sandy', address: 'Ocean blvd 2'},
{
_id: 58fdbf5c0ef8a50b4cdd9a8a , name: 'Betty', address: 'Green Grass 1'},
{ _id:
58fdbf5c0ef8a50b4cdd9a8b , name: 'Richard', address: 'Sky st 331'},
{ _id: 58fdbf5c0ef8a50b4cdd9a8c , name: 'Susan', address: 'One way
98'},
{ _id: 58fdbf5c0ef8a50b4cdd9a8d , name: 'Vicky', address: 'Yellow Garden 2'},
{ _id: 58fdbf5c0ef8a50b4cdd9a8e , name: 'Ben', address: 'Park Lane 38'},
{
_id: 58fdbf5c0ef8a50b4cdd9a8f , name: 'William', address: 'Central st 954'},
{ _id: 58fdbf5c0ef8a50b4cdd9a90 , name: 'Chuck', address:
'Main Road 989'},
{ _id: 58fdbf5c0ef8a50b4cdd9a91 , name: 'Viola', address: 'Sideway
1633'}]
method is the projection object that describes which fields to include in the result. This parameter is optional, and if omitted, all fields will be included in the result.
Return the fields "name" and "address" of all documents in the customers collection:
let MongoClient = require('mongodb').MongoClient;
let url = "mongodb://localhost:27017/";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
let dbo = db.db("mydb");
dbo.collection("customers").find({},
{ projection: { _id: 0, name: 1, address:
1 } }
).toArray(function(err, result) {
if (err) throw err;
console.log(result);
db.close();
});
});
Save the code above in a file called "demo_mongodb_find_fields.js" and run the file:
Run "demo_mongodb_find_fields.js"C:\Users\
>node demo_mongodb_find_fields.js Which will give you this result: [
{ name: 'John', address: 'Highway 71'},
{ name: 'Peter', address: 'Lowstreet 4'},
{
name: 'Amy', address: 'Apple st 652'},
{ name: 'Hannah', address:
'Mountain 21'},
{ name: 'Michael', address: 'Valley 345'},
{ name: 'Sandy', address: 'Ocean blvd 2'},
{
name: 'Betty', address: 'Green Grass 1'},
{ name: 'Richard', address: 'Sky st 331'},
{ name: 'Susan', address: 'One way
98'},
{ name: 'Vicky', address: 'Yellow Garden 2'},
{ name: 'Ben', address: 'Park Lane 38'},
{
name: 'William', address: 'Central st 954'},
{ name: 'Chuck', address:
'Main Road 989'},
{ name: 'Viola', address: 'Sideway
1633'}] You are not allowed to specify both 0 and 1 values in the same object (except if one of the fields is the _id field). If you specify a field with the value 0, all other fields get the value 1, and vice versa:
This example will exclude "address" from the result:
let MongoClient = require('mongodb').MongoClient;
let url = "mongodb://localhost:27017/";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
let dbo = db.db("mydb");
dbo.collection("customers").find({},
{ projection: { address: 0
} }
).toArray(function(err, result) {
if (err) throw err;
console.log(result);
db.close();
});
});To exclude the _id field, you must set its value to 0:
This example will return only the "name" field:
let MongoClient = require('mongodb').MongoClient;
let url = "mongodb://localhost:27017/";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
let dbo = db.db("mydb");
dbo.collection("customers").find({},
{ projection: { _id: 0, name: 1
} }
).toArray(function(err, result) {
if (err) throw err;
console.log(result);
db.close();
});
});This example will give you the same result as the first example; return all fields except the _id field:
let MongoClient = require('mongodb').MongoClient;
let url = "mongodb://localhost:27017/";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
let dbo = db.db("mydb");
dbo.collection("customers").find({},
{ projection: { _id: 0
} }
).toArray(function(err, result) {
if (err) throw err;
console.log(result);
db.close();
});
});You get an error if you specify both 0 and 1 values in the same object (except if one of the fields is the _id field):
let MongoClient = require('mongodb').MongoClient;
let url = "mongodb://localhost:27017/";
MongoClient.connect(url, function(err, db) {
if (err) throw err;
let dbo = db.db("mydb");
dbo.collection("customers").find({},
{ projection: { name: 1, address: 0
} }
).toArray(function(err, result) {
if (err) throw err;
console.log(result);
db.close();
});
});As you can see from the result of the example above, the result can be converted into an array containing each document as an object. To return e.g. the address of the third document, just refer to the third array object's address property:
Return the address of the third document:
console.log(result[2].address);