MongoDB Queries Using Nodejs

Here we will learn Mongodb Queries with the help of one example, below in the image list of all queries which we learn using nodejs:

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First need to make connection with mongodb client:

const MongoClient = require("mongodb").MongoClient;

//update the connection string.
const url = "mongodb://localhost/mongo-task";

//update database name
const dbName = "mongo-task";

//update collection name (i.e targetted collection)

const collectionName = "cars";

/*Query results are logged on the terminal.*/

Solution of Query 1:

//Query 1
numberOfColoursByManufacturer = async () => {
  const client = await MongoClient.connect(url, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
  }).catch((err) => console.log("Could not connect to MongoDB", err));

  try {
    const db = client.db(dbName);
    const collection = db.collection(collectionName);
    let res = await collection
      .aggregate([
        {
          $unwind: "$Colour",
        },
        {
          $group: {
            _id: "$Manufacturer",
            Colours: { $addToSet: "$Colour" },
          },
        },
        {
          $project: {
            _id: 0,
            Manufacturer: "$_id",
            CountOfColours: { $size: "$Colours" },
          },
        },
      ])
      .toArray();
    console.log(res);
  } catch (err) {
    console.log("Error occured in First Query");
  } finally {
    client.close();
  }
};

Solution of Query 2:

//Query 2
extrasByManufacturer = async () => {
  const client = await MongoClient.connect(url, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
  }).catch((err) => console.log("Could not connect to MongoDB", err));

  try {
    const db = client.db(dbName);
    const collection = db.collection(collectionName);
    let res = await collection
      .aggregate([
        {
          $unwind: "$Extras",
        },
        {
          $group: {
            _id: "$Manufacturer",
            Extras: { $addToSet: "$Extras" },
          },
        },
        {
          $project: {
            _id: 0,
            Manufacturer: "$_id",
            Extras: "$Extras",
          },
        },
      ])
      .toArray();
    console.log(res);
  } catch (err) {
    console.log("Error in Sec Query", err);
  } finally {
    client.close();
  }
};

Solution of Query 3:

//Query 3
countNumberOfExtras = async () => {
  const client = await MongoClient.connect(url, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
  }).catch((err) => console.log("Could not connect to MongoDB", err));

  try {
    const db = client.db(dbName);
    const collection = db.collection(collectionName);
    let res = await collection
      .aggregate([
        {
          $group: {
            _id: "$Model",
            Extras: { $push: "$Extras" },
            Avg: { $avg: { $size: "$Extras" } },
          },
        },
        {
          $project: {
            _id: 0,
            Model: "$_id",
            CountOfExtras: {
              $size: {
                $reduce: {
                  input: "$Extras",
                  initialValue: [],
                  in: { $setUnion: ["$$value", "$$this"] },
                },
              },
            },
            Avg: "$Avg",
          },
        },
      ])
      .toArray();
    console.log(res);
  } catch (err) {
    console.log("Error in Third Query", err);
  } finally {
    client.close();
  }
};

Solution of Query 4:

//Query 4
lowestValPerManufacturer = async () => {
  const client = await MongoClient.connect(url, {
    useNewUrlParser: true,
    useUnifiedTopology: true,
  }).catch((err) => console.log("Could not connect to MongoDB", err));

  try {
    const db = client.db(dbName);
    const collection = db.collection(collectionName);

    const res = await collection
      .aggregate([
        {
          $group: {
            _id: "$Manufacturer",
            price: {
              $min: {
                $add: ["$Price", "$Milage"],
              },
            },
          },
        },
        {
          $project: {
            _id: 0,
            Manufacturer: "$_id",
            LowestPrice: "$price",
          },
        },
      ])
      .toArray();
    console.log(res);
  } catch (err) {
    console.log("Error in Fourth Query", err);
  } finally {
    client.close();
  }
};

// To execute one query comment the others.

async function run() {
  await numberOfColoursByManufacturer();
  //await extrasByManufacturer();
  //await countNumberOfExtras();
  //await lowestValPerManufacturer();
}

run();

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Here you can also get help in:

• NodeJs Project Help Using MongoDB

• MongoDB Basic to Advance level Queries

• MongoDB Assignment Help

• MongoDB Project Help

• MongoDB Homework Help