Mongo Insert, Update, Remove query | Projection in MongoDB | Sort, Limit and Relation

Start server and mongodb using mongodb shell after installation which we discuss how to install mongodb in previous blog.

1. Insert record:

Before running insert query find collection with one row and all attributes to understand it easily.

Run db.collectionname.findOne().

>db.inspections.findOne

Question- Insert the record in collection "inspections" where

"id":"10021-2015-ENFP",

"certificate_number":9278809,

"business_name" : "Codersarts", "date" : "Feb 20 2019",

"result" : "No Violation Issued",

"sector" : "Cigarette Retail Dealer - 127".

2. Remove(delete) record:

If we want to remove by record with all column attribute than run query accordingly.

Remove(delete) by given criteria(condition): Run given all query to see how it work according to criteria

> db.inspections.find({})

>criteria = {"result" : "No Violation Issued"}

>db.inspections.find(criteria)

>db.inspections.remove(criteria)

if you want to delete only one document of given criteria then use

>db.inspections.remove(criteria,1)

It delete only one record from top as per given

criteria(condition)

3. Update

Question- Update multiple column value in database where put "result"= "Violation Issued" at the place of "result"="Pass" in all database.

> db.inspections.find({})

4- Projection in MongoDB:

A projection query is a query where you specify which fields should be returned.

You can do this by including the field names in your query, and adding a 1 or 0 next to them, to specify whether it should be returned or not. This is a projection parameter.

A projection parameter of 1 will display the field and a 0 will hide it.

Now, let's use projection to display just the date,result and except id field field:

>db.inspections.find( { "result": "Violation Issued" }, { "_id":0,"date": 1 ,"result":1} )

Result:

You can't mix 1s(inclusion) and 0s(Exclusion) like:

>db.inspections.find( { "result": "Violation Issued" }, { "date": 1, "sector":0 } )

Result: show error:

5- Limit the Results of a Query:

Return only the number of documents you need with the limit() method.

In MongoDB, you can use the limit() method to specify a maximum number of documents for a cursor to return.

When you query a collection using the db.inspections.find() method, you can append limit() to specify the limit.

Ok, so let's limit the results to say, 3 documents:

>db.inspections.find( { "result": "Violation Issued" }, { "date": 1 } ).limit(3)

6- Skip() Method:

You can use the skip() method to skip to a document within the cursor.

Skip first result and display next three result

Note that skip() can be used on any query (not just ones with limit()).

7- Sort the Results of a Query:

The sort() method specifies a sort order for the cursor.

It will typically contain one or more fields, each followed by either 1 or -1, depending on whether the sort should be in ascending or descending order.

With sort() in Ascending Order:

A value of 1 next to a field name specifies that the documents should be sorted by the specified field in ascending order.

Here we sort the results by name in ascending order:

>db.inspections.find( ).limit(3).sort( { "result": 1} )

With sort() in Descending Order:

A value of -1 next to a field name specifies descending order.

Here we sort the results by name in descending order:

>db.inspections.find( ).limit(3).sort( { "result": -1} )

Multiple Fields

>db.inspections.find( ).sort( { "result": 1, "date": -1 } )

8- Create a Relationship:

To create a relationship in MongoDB, either embed a BSON document within another, or reference it from another.

One-to-One Relationship One-to-Many Relationship

Querying the Relationship:

you can use $lookup to perform a left outer join on the two collections.This, in conjunction with the aggregate() method, and $match.

Example:

>db.collection1.aggregate([

    {

      $lookup:

        {

          from: "collection2",

          localField: "_id",

          foreignField: "artist_id",

          as: "band_members"

        }

   },

   { $match : { artistname : "Rush" } }

]).pretty()

May I hope you this blog provide you some important query in MongoDB which help you to run easily on the project.

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