Today in this article, we will learn to perform MongoDB – Get the last N records OR most recent records. There are easy approaches to achieving the last N records or most records in the mongo document.

We will cover a few approaches to Get the last N records OR most recent records.

Overall, We will cover the below aspects,

I have below Mongo Collection where my fields are defined as below.

I have a field name called “UserID” which is of type “Int“. I want to use this field to query first “N” element from MongoDB.

Command:

Command to get the first N element in MongoDB

db.<Collection>.find().sort({<field>:1}).limit(N)

The above query will give records based on Ascending order of field value.

 db.<Collection>.find().sort({<field>:-1}).limit(N) 

Similarly, the above query will give records based on descending order of field value.

Example :

Get the last 2 records in MongoDB

Ascending order,

db.Books.find().sort({UserId:1}).limit(2)

OR

Descending Order,

db.Books.find().sort({UserId:-1}).limit(2)  

db.Books.find().sort({UserId:1}).limit(2)

{ "_id" : ObjectId("62c5dd1902514a766441e2ee"), "UserId" : 555, "Books" : [ { "book_name" : "book_name1", "price" : "88", "category" : [ { "key" : "Test1", "value" : 123 } ] }, { "book_name" : "book_name2", "price" : "50", "category" : [ { "key" : "test2-1", "value" : null }, { "key" : "test4", "value" : null } ] } ], "value" : null }

{ "_id" : ObjectId("6382cfa8c592b1532c8d5bcb"), "UserId" : 934, "DateAdded" : ISODate("2022-01-01T05:00:00Z"), "Books" : [ { "book_name" : "book_name1", "price" : null, "category" : [ { "key" : "Test1", "value" : null } ] }, { "book_name" : "book_name2", "price" : "50", "category" : [ { "key" : "test

Get the last 50 records in MongoDB

db.Books.find().sort({UserId:-1}).limit(50)

Get the last 100 records in MongoDB

 db.Books.find().sort({UserId:-1}).limit(100) 

Command to get the recent record in MongoDB

Command:

Command to get the most recent records in MongoDB

If you have a date field already in the MongoDB document then you can sort the most recent documents based on dates.

db.<Collection>.find().sort({<DateField>:-1}).limit(N)

OR

 db.<Collection>.find().sort({_id:-1}).limit(N) 

If your Mongo records use default ObjectID, then this _id will have a default insertion time that is unique and can be used to get records.

Example

db.Books.find().sort({DateAdded:1}).limit(5)

OR

 db.Books.find().sort({_id : -1}).limit(5) 

db.Books.find().sort({DateAdded:1}).limit(5)

{ “_id” : ObjectId(“62c5dd1902514a766441e2ee”), “UserId” : 555, “Books” : [ { “book_name” : “book_name1”, “price” : “88”, “category” : [ { “key” : “Test1”, “value” : 123 } ] }, { “book_name” : “book_name2”, “price” : “50”, “category” : [ { “key” : “test2-1”, “value” : null }, { “key” : “test4”, “value” : null } ] } ], “value” : null }
{ “_id” : ObjectId(“62c5e3f602514a766441e2ef”), “UserId” : 6777, “DateAdded” : ISODate(“2019-01-01T05:00:00Z”), “Books” : [ { “book_name” : “book_name1”, “price” : null, “category” : [ { “key” : “Test1”, “value” : null } ] }, { “book_name” : “book_name2”, “price” : “50”, “category” : [ { “key” : “test3”, “value” : null }, { “key” : “test4”, “value” : null } ] } ], “value” : null }
{ “_id” : ObjectId(“6382cfbec592b1532c8d5bcc”), “UserId” : 6777, “DateAdded” : ISODate(“2021-01-01T05:00:00Z”), “Books” : [ { “book_name” : “book_name1”, “price” : null, “category” : [ { “key” : “Test1”, “value” : null } ] }, { “book_name” : “book_name2”, “price” : “50”, “category” : [ { “key” : “test3”, “value” : null }, { “key” : “test4”, “value” : null } ] } ], “value” : null }
{ “_id” : ObjectId(“6382cfa8c592b1532c8d5bcb”), “UserId” : 934, “DateAdded” : ISODate(“2022-01-01T05:00:00Z”), “Books” : [ { “book_name” : “book_name1”, “price” : null, “category” : [ { “key” : “Test1”, “value” : null } ] }, { “book_name” : “book_name2”, “price” : “50”, “category” : [ { “key” : “test3”, “value” : null }, { “key” : “test4”, “value” : null } ] } ], “value” : null }

If you don’t have a Date field, you can still use the inbuilt default date object for getting recent documents.

Please refer to this article for more details,

• Query MongoDB using ObjectId by Date -MongoShell

Do you have any comments or ideas or any better suggestions to share?

Please sound off your comments below.

Happy Coding !!

Please bookmark this page and share it with your friends. Please Subscribe to the blog to receive notifications on freshly published (2025) best practices and guidelines for software design and development.

The post MongoDB – Get the last N records OR most recent records first appeared on TheCodeBuzz.

Today in this article, we will learn MongoDB Change The Type of a field. There are multiple approaches to achieving the data type change as explained below,

• Change data type using Mongo Compass UI or any other UI –Manual way
• Change data type in Mongo Using Aggregation Type Expression Operators – An automated way
  • Using Aggregation Operators like $toInt , $toString
  • Using Aggregation Operators like $convert

We will cover various 3-4 approaches to perform the datatype change feature.

Overall, We will cover the below aspects,

The below approach discussed is very useful when you don’t want to delete or drop the mongo fields but rather want to change the type of a field.

I have below Mongo Collection where my fields are defined as below.

I have a field name called “EmpID” which is of type “string“. I want to change this field to “int” using MongoShell.

Change data type using Mongo Compass UI or any other UI –Manual way

One can easily change the data type of a field in the Mongo DB document

In Mongo Atlas click on Edit Document. Here you will get an option to choose the data type,

As shown above, the manual approach can be used as needed.

Change data type in Mongo Using Aggregation Type Expression Operators – An automated way

Please open the command prompt or Mongo shell and log in to your database using a connection string.

We will first login to MongoDB and then switch to using the required database and the collection

Command Pattern

db.<collection-name>.update( {}, [ {$set:{ "<field-name>" : {$<field type>: "$<field-name>"}}} ]

Example – Convert string to numerical values in MongoDB

Example

db.employee.update({}, [ {$set:{ "EmpID" : {$toInt: "$EmpID"}}} ], {multi:true})
WriteResult({ "nMatched" : 1, "nUpserted" : 0, "nModified" : 1 })

Example – Convert a numeric value to a string in MongoDB

Command:

db.employee.update({}, [ {$set:{ "EmpID" : {$toString: "$EmpID"}}} ], {multi:true})

Example

db.employee.update({}, [ {$set:{ "EmpID" : {$toString: "$EmpID"}}} ], {multi:true})
WriteResult({ "nMatched" : 5, "nUpserted" : 0, "nModified" : 5})

Example – Convert a NumberLong to a String

Command:

db.employee.update({}, [ {$set:{ "Ssn" : {$toString: "$Ssn"}}} ], {multi:true})

In the above example, Ssn is a long number data type field that we are converting to string type.

Using Aggregation Operators like $convert

Using this option, one can easily create an aggregation pipeline using $Convert operation which lets you convert field type easily.

Example:

db.employee.aggregate(
  [
    {
      $project:
        { 
          result: 
          {
            $convert: { 
              input: "$EmpID", 
              to: "string",
              onError: "An error occurred for the conversion",
              onNull: "Input was null or empty" 
            }
          }
        }
    }
  ]
).pretty()

With pretty print, you can get the expression results on the screen as shown above.

Do you have any comments or ideas or any better suggestions to share?

Please sound off your comments below.

Happy Coding !!

Please bookmark this page and share it with your friends. Please Subscribe to the blog to receive notifications on freshly published (2025) best practices and guidelines for software design and development.

The post MongoDB Change The Type of a field – Guidelines first appeared on TheCodeBuzz.

Today in this article, we will see how to search records in MongoDB does not contain a string.

We will learn to search a string and match documents based on case-sensitive and insensitive searches in this informative article.

Multiple approaches are covered, including using a like query or regex query.

We will see multiple approaches to achieve the same like using a like query or regex query etc.

Today in this article, we will cover below aspects,

Let’s take the example below to learn the query.

I have a sample MongoDB document below in one of the collections.

[
  {
    "_id": "5db5a4476997188b2722c820",
    "Name": "Design Patterns",
    "Price": 54.93,
    "Category": "Computers",
    "Author": "Ralph Johnson"
  },
  {
    "_id": "5ff50353a29ce9564c2724e2",
    "Name": "Design Patterns",
    "Price": 54.93,
    "Category": "Computers",
    "Author": "Mike Casper"
  },
  {
    "_id": "5ff503cda29ce9564c2724e3",
    "Name": "Design Patterns",
    "Price": 54.93,
    "Category": "Computers",
    "Author": "Julia Robert"
  },
 {
    "_id": "5f34a2430c3ca98a8c9052d2",
    "Name": "Design Patterns",
    "Price": 54.93,
    "Category": "Computers",
    "Author": "Mike Johnson"
  }
]

MongoDB does not Contain a String

Let’s build a MongoDB query using a regex for getting documents that don’t contain a String.

Author names where the name contains a word like “John” or “john” for the Author field value.

Here we are trying to match “John” or “john” could be contained at the start or last or in the middle or anywhere else of Author names.

MongoDB does not Contain a String – Case sensitive

Command

{ Field Name : {'$regex' : '^((?!Field Value).)*$'}}

Example

db.Books.find( { {Author:{'$regex' : '^((?!John).)*$'}} )

Mongo Query Result :

MongoDB does not Contain a String – Case insensitive

Command

{Field Name :{'$regex' : '^((?!Field Value).)*$', '$options' : 'i'}}

Example

{Author: {$regex: '^((?!John).)*$',$options: 'i'}}

References :

• MongoDB Naming Standards and Guidelines

Do you have any comments or ideas or any better suggestions to share?

Please sound off your comments below.

Happy Coding !!

Please bookmark this page and share it with your friends. Please Subscribe to the blog to receive notifications on freshly published (2025) best practices and guidelines for software design and development.

The post MongoDB does not Contain a String query with examples first appeared on TheCodeBuzz.

Today in this short tutorial, we will see how to Mock and Unit Test MongoCollection and IMongoCollection used in the MongoDB .NET driver library.

MongoCollection mocking could be useful considering the complex extension method supported by MongoDB drivers which is not only difficult to mock but also unit tested.

Below is a sample code for the Mocking MongoCollection class

        var settings = new MongoCollectionSettings();
            var mockCollection = new Mock<IMongoCollection<Book>> { DefaultValue = DefaultValue.Mock };
            mockCollection.SetupGet(s => s.DocumentSerializer).Returns(settings.SerializerRegistry.GetSerializer<Book>());
            mockCollection.SetupGet(s => s.Settings).Returns(settings);
            return mockCollection;

Above the “Book” class is a model object supporting book schema within the MongoDB database.

public class Book
    {
        [BsonId]
        [BsonRepresentation(BsonType.ObjectId)]
        public string Id { get; set; }

        public string BookName { get; set; }

        public decimal Price { get; set; }

        public string Category { get; set; }

        public string Author { get; set; }
    }

Below is a sample example using the above mock scenario,

       [Fact]
        public async void Test_GetBooksAsync_Verify()
        {
            //Arrange
            var mockContext = new Mock<IMongoContext>();
            var mockCollection = CreateMockCollection();
            var collection = mockCollection.Object;

            Book document = new Book();
            document.Author = "asdas";
            document.BookName = "sadasd";
            document.Id = ObjectId.GenerateNewId().ToString();
            mockCollection.Object.InsertOne(document);

            BookstoreDatabaseSettings setting = new BookstoreDatabaseSettings();
            setting.BooksCollectionName = "Book";
            var mockIDBsettings = new Mock<IOptions<BookstoreDatabaseSettings>>();

            mockContext.Setup(x => x.GetCollection<Book>("Book")).Returns(mockCollection.Object);
            mockIDBsettings.Setup(x => x.Value).Returns(setting);

            //Act

            BookService service = new BookService(mockIDBsettings.Object, mockContext.Object);
            var result = await service.GetBooksAsync();

            //ASSERT
            mockContext.Verify(x => x.GetCollection<Book>("Book"), Times.Once);
            mockCollection.Verify(m => m.FindAsync<Book>(FilterDefinition<Book>.Empty, null, CancellationToken.None), Times.Once);
        }

Above extension, methods are Asserted for verifying, if they are called in the code execution or not. Additionally, you can add more assertions for the results you get from the method. Please visit this article for more information on how to verify controller methods

Do you have any comments or ideas or any better suggestions to share?

Please sound off your comments below.

Happy Coding !!

Please bookmark this page and share it with your friends. Please Subscribe to the blog to receive notifications on freshly published (2025) best practices and guidelines for software design and development.

The post MongoDB – Mock and Unit Test MongoCollection first appeared on TheCodeBuzz.

Today this article will see how to write a query in MongoDB to find the objects between two dates. We shall see examples with dates using timestamp fields (if available) or using Mongo-defined timestamp available via _Id as objectId.

Today in this article, we will cover below aspects,

Approaches to get the records between two dates,

• Using the dates field if exist

• Using MongoDB _Id ObjectId field

We will see greater than or less than date queries using CLI or Compass UI.

Getting started

Using the Custom Date field (if available)

Do you follow schema-driven development?

If your schema already has any date or timestamp field then you can use the same to query to get all the records. Here below is a sample schema or document we shall use where I have a custom date field called “DateAdded“

Example:

{
  "_id": "62c5e3f602514a766441e2ef",
  "UserId": 999999,
  "DateAdded": "2021-01-01T05:00:00.000Z",
  "Books": [
    {
      "book_name": "book_name1",
      "price": 88,
      "category": [
        {
          "key": "Test1",
          "value": "60"
        }
      ]
    },
    {
      "book_name": "book_name2",
      "price": 50,
      "category": [
        {
          "key": "test3",
          "value": "60"
        },
        {
          "key": "test4",
          "value": "100"
        }
      ]
    }
  ]
}

Find objects using CLI or Compass UI

Here we will be using the below query to get the documents between two dates in MongoDB Collection.

Find the MongoDB Documents when the Date is a greater specified date

Command

{ <Field Name>: { $gt:ISODate('Date here') } }

 

Find the MongoDB Documents date is less than the specified date

Command

{ <Field Name>: { $lt:ISODate('Date here') } }

For more details on other queries, please refer below article

• MongoDB Date Range query greater than or less than

Find the Objects using the _Id field i.e ObjectId

This is another approach typically useful when you don’t have any timestamp or date field in your schema.

As we know, MongoDB uses the _id field as ObjectId. This Id has few behavioral characteristics.

It is a 4-byte timestamp is a UNIX timestamp.

Timestamp represents the ObjectId’s creation timestamp when a document is inserted into Mongo collection first time, measured in seconds since the Unix epoch. for more details, please visit here.

Command

{ <field Name>: { $gt: ObjectId.fromDate( new ISODate("Date here"))}}

OR

 <field Name>: { $lt: ObjectId.fromDate( new Date("Date here"))}} 

Do you have any comments or ideas or any better suggestions to share?

Please sound off your comments below.

Happy Coding !!

Please bookmark this page and share it with your friends. Please Subscribe to the blog to receive notifications on freshly published (2025) best practices and guidelines for software design and development.

The post MongoDB to Find the Objects between two dates first appeared on TheCodeBuzz.