Connect Flutter app with MongoDB

To connect and perform CURD operations use any driver package available on pub.dev. mongo_dart package offer everything we need and it is pretty popular than others.

A prerequisite for using the dart package is that configure Mongo Cluster.  

• Configuring MongoDB cluster for Flutter

Mongo_dart package

Mongo dart package is one of the most used one for connecting MongoDB with dart. You can grab the connection string from the MongoDB or just use the given code and put it in an async function.

For connecting MongoDB we need

1. Import the mongo_dart package / add package dependency
2. MongoDB user id and password
3. MongoDB name

Setup the dependency as follows and import Mongo 

dependencies:
  flutter:
    sdk: flutter 
  mongo_dart: "^0.4.4" 

import 'package:mongo_dart/mongo_dart.dart';

The connection string

"mongodb+srv://<user>:<password>@cluster0.cqnll.mongodb.net/<database>?retryWrites=true&w=majority");

The connection string consist of username, password and database name which required to access , (this is a access anywhere connection string) . Let create a Db instance and invoke the database. 

 load() async {
   
      var db = await _MongoDB.Db.create(
          "mongodb+srv://admin:text123@cluster0.cqnll.mongodb.net/projectdata?retry
           Writes=true&w=majority");
       
      await db.open();
}

To access collections you need to use db.collection as follows

var coll = db.collection('projectdocs');

Find

To get all  the elements we can use find with zero arguments

var rs = await coll.find();
await rs.forEach((element) {
print(element['_id]);
}

Searching for specific documents can be achieved by using find({‘eid’:’u7867′}). 

• Find documents by objectId using mongo_dart package in Flutter
  
  

  Mongodb ObjectID (_id) is a Bson object which can be used search documents, and also for update and delete. The _id is unique and contain many properties like timestamp etc. We can use it on mongo console as follows

  db.todos.find()
  { _id: ObjectID("5f9ae45b6acbd21070cb75d8"),
    item: 'Write next tutorial',
    __v: 0 }
  { _id: ObjectID("5f9ae4776acbd21070cb75db"),
    item: 'Pay insurance premiums',
    __v: 0 }
  { _id: ObjectID("5f9ae4856acbd21070cb75dc"),
    item: 'Reserve movie tickets for Monday',
    __v: 0 }
  { _id: ObjectID("5f9d7b49f38c36015cacf0d0"),
    item: 'create a tutorial - express app in a minute',
    __v: 0 }
  { _id: ObjectID("5fa0ba682bee610055bfaf6a"),
    item: 'something',
    __v: 0 }
  { _id: ObjectID("5fa6d7c4f6bd2400550bf125"),
    item: 'asdad',
    __v: 0 }
  { _id: ObjectID("5fa6da2df6bd2400550bf126"),
    item: 'setup a flutter mongodb',
    __v: 0 }
  db.todos.find({'_id': ObjectId("5fa6da2df6bd2400550bf126")})
  { _id: ObjectID("5fa6da2df6bd2400550bf126"),
    item: 'setup a flutter mongodb',
    __v: 0 }
  

  

  In Flutter

  In Flutter you have the Mongo Dart package to access the MongoDB, which offer same type of CURD commands. While you use the following format of find function you may catch the errors.

  var coll=db.Collections('todos');
  var docs=coll.find({'_id': 'ObjectId("5fa6da2df6bd2400550bf126")'});
  
  

  Solution

  As I told before the hexa string “5fa6da2df6bd2400550bf126“ is a Bson object.  To use it with find/update we have to use ObjectId instead of  hexa string.  The dart package also provide ObjectID class to convert the string  into ObjectId type and then we can use it as follows

  ObjectId objId = _MongoDB.ObjectId.parse("5fa6da2df6bd2400550bf126");
  var docs=coll.find({'_id': objId});
  

  and it will work as expected.

  Like this:

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  Related

New Document

For inserting new document to the MongoDB collection we can use insert command as follows

collection.insert({
'eid':'d345',
'name':'Mohan Kumar'
});

findAndModify ()

This method can be used to search and modify documents in the collection. Following is a sample update statement.

var pid='rt76';
coll.findAndModify(query: {
  'pid': pid
}, update: {
  'projectName': value.projectName,
  'projectDesc': value.projectDesc,
  });

This will find document with pid  rt76  and update the document with new one ( passed in ‘update:’ )

Deletion

It can be performed using find and remove command. For emptying the collection we can use the remove commandFromCollection

db.removeFromCollection('projectdocs');

command which accept the a collection name.