8 posts tagged with "nosql"

Traditional Architecture :​

In a traditional Application with the normal approach, transactional use-cases usually involve persisting data in a few SQL tables or in a NOSQL database. When the changes are performed on the object the database is updated to match the new state.

The traditional approach works well in case if you do not need to know the changes that object has gone through, but in modern systems customers always comes up with a requirement to get the log of changes that particular entity has gone through. With the traditional approach, there is no way of knowing what the user had in the object before changing it, or at which point of time the contents changed. We can still solve this with the traditional way by storing the extra information about the modifications but the solution becomes more complex.

For example in traditional approach,

https://gist.github.com/sajeetharan/2d9921571c67f7038ec5a4053882b85f

Which will create an entry for each insert in the SQL database as follows,

The current state is saved in a relational database. We load the object, change it and save  it back.

EventSourcing Architecture :​

In the eventsourcing solution, we look at the problem as a sequence of events that occur and save the occurrence of events as it is. The events contains all details about what actually happened at particular point of time. These are historical information and once it is saved it should not be modified.

https://gist.github.com/sajeetharan/825ec83fd780b7670146649bf6d4a0ce

All events for a certain product are stored. Their data and sequence define the current state of the product. Event is the easiest way to remember what happened at a certain time. Event sourcing comes with an advantage of having audit trail by itself and to get full understanding of what the system is doing.

Event Sourcing Architecture with AzureCosmosdb and EventHub

To implement event sourcing in your application, Microsoft azure provides the following services to  full fledged solution and we will discuss in this blog.

Lets look at the diagram below,

Application 1 stores the data in the traditional database and your customer needs the changes that has been done on the product. The above architecture will easily fulfill the requirement with the event sourcing.

Components involved in the architecture as follows,

Azure EventHub​

Azure Eventhub is a managed service to receive and process millions of events per second. It is intended to handle event based messaging in huge scale. This could be used in an product if you have devices application publishing events and send them to eventhub. It will create a stream of all these events which can be read by different applications in different ways. Eventhub provides interfaces such as AMQP and HTTP to make it easy to send messages to it. In Eventhub we can define consumer groups which lets us to read stream of events. We can decide on consumer group based on the number of receivers(applications)

CosmosDB​

Azure Cosmos DB is a globally-distributed, multi-model database as a service build for low latency and elastic scalability.  It supports the following options to store the data and it is highly available from anywhere in the world,

• Key-value
• Column-family
• Document: MONGO or SQL
• Graph

I will be not going in detail as there are enough blogs to get started with CosmosDB. In the above architecture there will be millions of events created after each update hence we need to store them in the cosmosdb with the state of the object. This way brings a lot of benefits. First, the event store with cosmosdb becomes your canonical source of truth that describes the updates applied to your domain in an unbiased form.

Implementation:

Application 1:

Whenever user updates an object in the application1, there will be notification message sent to the EventHub with an ID (unique id for each message) that something has happened on application. We could make use of epoch timestamp with 8 digits to make sure it is a unique one. A sample payload would look like,

{"MessageId": 1547632386819}

Note:  As Eventhub can have a message of maximum size 256k it is always better to have minimum size of message.

Once the notification is sent, the state of the object is stored in the eventstore(cosmosdb).

Application 2:

Application 2 will have an EventHub receiver which runs on the background which will subscribe to the EventHub and get the latest message. Once the id is retrieved by the receiver, it can request the eventstore with the id and get all the changes prior to the id as follows,

https://gist.github.com/sajeetharan/c34965a606c8afff9d02f2a3a17522bf

which will create the documents in Cosmosdb as,

With the above approach ensures that all changes to product are stored as sequence of events. When we look at broader picture, it also ensures that all changes to application state are stored.

This is the simple architecture diagram to implement event sourcing in your application. One of the very good pattern to implement event sourcing is by using CQRS(Command Query Responsibility Segregation).

Lets look at the etail implementation with the code in the upcoming blogs. Hope this will help someone out there to implement event sourcing in your application if you are using Azure platform.

Azure CosmosDB (Azure Cosmos DB – Globally Distributed Database Service (formerly DocumentDB) | Microsoft Azure) is a super set of the service once known as “Azure Document Db”. In short: “Azure CosmosDB ” = “Azure Document Db” + new data types + new APIs.

You can try CosmosDB  for free on Azure or you can setup the CosmosDB on your local environment by following my previous blog. I am becoming a fan of .NET Core with all the features and it is getting better day by day . In this blog post i just wanted to take that initial steps of how to work with CosmosDB from .NET Core Client context. After reading this blog, you should be able to do the following with CosmosDB programmatically,

• Create Database
• Create Collection
• Create Documents
• Query a Document
• Delete Database

Pre-Requisities Needed:

I have the following in my local environment , hope you guys have already have😊, if not start setting up.

• Windows 10 OS
• Azure CosmosDB Emulator
• Visual Studio Code editor with C# plugin
• .NET Core 2.0

Ok folks, lets get started.

Step 1: Create .Net Core Console Application :  As other tutorials, to make it simple I will be creating a dotnetcore console app to work with CosmosDB . With Net Core , we now  have a CLI. Lets create the new app with the following steps. (I’ve mentioned in the previous blog)

1. Open command prompt or poweshell (Administrator Mode)
2. Navigate to your folder where you need to create the app
3. Execute the following command

dotnet new console -n CosmosCoreClient -o CosmosCoreClient

here -n denotes the name of the application, and -o tells the CLI to create a folder with that name and create the application inside the folder

Open the newly created project in Visual Studio Code. Execute the following command

Code.

Here is a screenshot of how it should look on your end:

I am using C# 7.1 feature to create a async Main method in my console app. For that, we will need to make a small change in our project file a little. Open CosmosDBClient.csproj file to edit. Add the following XML node to PropertyGroup node.

<LangVersion>latest</LangVersion>

After changes, your csproj file should look like below:

Lets move to the core part of integrating CosmosDB with .netCore application and start building the features.

Step 2: Add CosmosDB Nuget Package

If you have followed the above steps, we have successfully created the application, next is to add reference to CosmosDB nuget package to get the client libraries. Advantage of these packages/libraries are, they make it easy to work with Cosmosdb.

1. Open a command prompt and navigate to root of your project.
2. Execute the following command

dotnet add package Microsoft.Azure.DocumentDB.Core

You might wonder the namespace has DocumentDB in it. In fact DocumetDB is where the whole journey started and hence the name sticks in Cosmos world too. If you now look at the project file a new reference for DocumentDB would have been added. Here is the screenshot of my project file.

Step 3: Creating Model for CosmosDB

Lets build the database. If you are new to CosmosDB you should know that CosmosDB has a query playground here https://www.documentdb.com/sql/demo. It is a sandboxed environment with couple of databases and you can try around with different queries you can write against the database. For this post, lets create the database named Course locally.

Since we our application is to deal with the Courses we need 4 Models here.

1. Course
2. Session
3. Teacher
4. Student

Here are the Models of the above 4.

Course.cs

using Microsoft.Azure.Documents;
using Newtonsoft.Json;
using System;
using System.Collections.Generic;
public class Course : Document
{
    [JsonProperty(PropertyName = "CourseId")]
    public Guid CourseId { get; set; }

    [JsonProperty(PropertyName = "Name")]
    public string Name
    {
        get
        {
            return GetPropertyValue<string>("Name");
        }
        set
        {
            SetPropertyValue("Name", value);
        }
    }

    [JsonProperty(PropertyName = "Sessions")]
    public List<Session> Sessions { get; set; }

    [JsonProperty(PropertyName = "Teacher")]
    public Teacher Teacher { get; set; }

    [JsonProperty(PropertyName = "Students")]
    public List<Student> Students { get; set; }
}

Session.cs

using System;

public class Session
{
    public Guid SessionId { get; set; }

    public string Name { get; set; }

    public int MaterialsCount { get; set; }
}

Teacher.cs

using System;

public class Teacher
{
    public Guid TeacherId { get; set; }

    public string FullName { get; set; }

    public int Age { get; set; }
}

Student.cs

using System;

public class Student
{
    public Guid StudentId { get; set; }
    public string FullName { get; set; }

}

Lets create the Client as the next step.

Step 4: Creating the Client

Next step you will need to instantiate the CosmosDb client before we do anything with the database. In order to connect to the local instance of the cosmosDb, we need to configure 2 things,

1. URL of the CosmosDb instane
2. Authentication key needed to authenticate.

As stated above, When you start the CosmosDb  local emulator, the db instance is available at https://localhost:8081. The authkey for local emulator is a static key and you can find it here in this article(https://docs.microsoft.com/en-us/azure/cosmos-db/local-emulator#authenticating-requests). This key works only with the local emulator and wont work with your Azure instance, you can find the key if you are using azure instance from the portal as mentioned in the answer. Here is the code snippet to instantiate the client:

        static string endpointUri = "https://localhost:8081";
        static string authKey = "C2y6yDjf5/R+ob0N8A7Cgv30VRDJIWEHLM+4QDU5DE2nQ9nDuVTqobD4b8mGGyPMbIZnqyMsEcaGQy67XIw/Jw==";
        string dbName = "CourseDB";
        string collectionName = "Courses";
        static void Main(string[] args)
        {
            Console.WriteLine("Press any key to run");
            Console.ReadLine();

            Run();

            Console.ReadLine();

        }
        private static async void Run()
        {
            DocumentClient documentClient = new DocumentClient(new Uri(endpointUri),
                authKey);
        }

When the method Run is exectued the Client is instantiated with the local CosmosDB emulator.

Step 5: Lets start building the features

Next step is to build the features as listed above. Lets add the methods inside the Async method.

Creating Database:

To create a new database programmatically, we make use of CreateDatabaseAsync() or CreateDatabaseIfNotExistsAsync(). When creating the database we pass the database name. Here is the code snippet:

private static async Task<Database> CreateDatabase(DocumentClient documentClient)
        {
            Database database = documentClient.CreateDatabaseQuery().Where(c => c.Id == "courseDatabase").AsEnumerable().FirstOrDefault();
            if (database == null)
            {
                database = await documentClient.CreateDatabaseAsync(new Database()
                {
                    Id = "courseDatabase"
                });
            }
            return database;
     }

When you refresh the URL of local CosmosDB emulator, You should see the database created in your local db emulator as follows,

Creating Collection:

Once the database is created, we can then create a collection. We make use of CreateDocumentCollectionAsync() or CreateDocumentCollectionIfNotExistsAsync().

We will need to provide what is known as the database link (basically the URI at which the db can be reached) and the collection name to the create method. Here is the code snippet.

private static async Task<DocumentCollection> CreateDocumentCollection(DocumentClient documentClient, Database database)

        {
            DocumentCollection documentCollection = documentClient.CreateDocumentCollectionQuery(database.CollectionsLink).Where(c => c.Id == "courseDocumentCollection").AsEnumerable().FirstOrDefault();

            if (documentCollection == null)
            {
                documentCollection = await documentClient.CreateDocumentCollectionAsync(database.SelfLink, new DocumentCollection()
                {
                    Id = "courseDocumentCollection"
                });
            }

            return documentCollection;
        }

Now you should the the Collection for Course is created as follows,

Creating Document :  After creating the database and collection, we can now create the documents. We make use of CreateDocumentAsync() for this purpose. We will need to pass the URI of the collection under which we want to create the document and the document data itself. In this example we make use of the Course data mode i showed earlier and pass it to the create method. Here is the code snippet:

private static async Task CreateCourse(DocumentClient documentClient, DocumentCollection documentCollection)
        {
            Course course = new Course()
            {
                CourseId = Guid.NewGuid(),
                Name = "En",
                Teacher = new Teacher()
                {
                    TeacherId = Guid.NewGuid(),
                    FullName = "Scott Hanselman",
                    Age = 44
                },
                Students = new List<Student>()
                {
                    new Student(){
                         FullName = "Trump",
                         StudentId = Guid.NewGuid()
                    }
                },
                Sessions = new List<Session>(){
                    new Session(){
                        SessionId = Guid.NewGuid(),
                        Name = "CosmosDB",
                        MaterialsCount = 10
                    },
                    new Session(){
                        SessionId = Guid.NewGuid(),
                        Name = "Ch1",
                        MaterialsCount = 3
                    }
                }
            };
            Document document = await documentClient.CreateDocumentAsync(documentCollection.DocumentsLink, course);
        }

You should see the document inserted in localdb Emulator as follows.

Querying Document:

Now that we have created a document, we can see how to query it. We can make use of CreateDocumentQuery() method for this purpose. We will need to pass the collection link on which we need to query. We can then build the query as a LINQ expression and the client library does the rest. This is the best part of the client library. It has the ability to translate your LINQ expression to cosmos REST URIs without me having to crack my head in constructing those URIs. Here is the code snippet:

private Course QueryCourse(Guid guid, String dbName, DocumentClient documentClient, string collectionName)
        {
            Course selectedCourse = documentClient.CreateDocumentQuery<Course>(
                             UriFactory.CreateDocumentCollectionUri(dbName, collectionName))
                             .Where(v => v.Name == "CosmosDB")
                             .AsEnumerable()
                             .FirstOrDefault();
            return selectedCourse;
        }

Note that you will need to import System.Linq for the LINQ expression to work.

Deleting Database:

Finally, we can make use of DeleteDatabaseAsync() method to delete the database programmatically. We will need to provide the database link to the delete method. We can use the UriFactory.CreateDatabaseUri() helper method to create the database link. Here is the code snippet:

await documentClient.DeleteDatabaseAsync(UriFactory.CreateDatabaseUri(dbName));

Well, those are the main features that Azure CosmosDB client provides and if you are stuck with any of the steps above , you can check out the repository i have added with the samples.

Happy Coding! Lets spread Azure's CosmosDB to the world.

Recently I started experimenting with Azure's CosmosDB and developed few applications using the same. To start with it this blog will help all the Azure/CosmosDB developers out there to easily setup with visual studio code. I will be sharing how to connect to Azure CosmosDB without using the portal in local machine.

To start with it, You should have visual studio code installed on your machine. If not download it from here.

We need to setup an extension with visual studio code as a initial step. Azure CosmosDB extension for visual studio code gives developers set of cool commands to work with CosmosDB. With the help of Azure CosmosDB extension developers can easily do the actions which could be done on the azure portal such as Create,delete,modify databases,Collections,views and documents. Also the hierarchical representation will provide a better way to understand the structure of database.

Step 1:

To start with, you must install the Azure CosmosDB from the market place. So, search for Azure Cosmos DB extension in the market place and click on install

Go to View - > Extensions or press Ctrl + Shift + X

Once the extension is installed, you can find Azure CosmosDB in explore section of visual studio code.

Step 2:

To explore the different types of commands with Azure Cosmos DB, open show all command palate and search for Cosmos. It will list down a different set of commands that you can play with,

Go to View - > Extensions or press Ctrl + Shift + P              

Step 3:

Now the extension is installed successfully. Lets see how to connect to Azure CosmosDB  in local machine. Move back to Azure CosmosDB extension section in the explorer panel. Sign in to Azure account to view the CosmosDB accounts inside the visual studio code alternatively you can select “Attach Database Account”

Select the specific Database Account API, in this case it is DocumentDB and enter the connection string copied from the portal

To get the connection string from the Azure Portal, navigate to the respective CosmosDB  Resource, and from the left side panel Settings –> Keys -> Connection String Copy the Primary Connection String.

Now you can see the database displayed with the account provided in the azure CosmosDB explorer pane.

That’s it Now you can Add, Modify Database, collection, and documents within Visual Studio Code. Play around with all the commands and features of the extension.

Step 4: Installing Azure Cosmos DB Emulator

Azure Cosmos DB Emulator provides a local environment that emulates the Azure CosmosDB service for your development. With the Azure Cosmos DB Emulator, you can develop and test your application locally, without creating an Azure subscription and without internet connection. With the extension we installed already you can connect with Local Emulator as well.

Download Azure CosmosDB emulator:

You can download emulator from Microsoft Download Center.

1. Extract setup and run emulator exe.
2. Once you completed the setup, type Azure Cosmos DB Emulator in Start menu.

Start the local Azure CosmosDB Emulator, and make sure it’s running.

Verify the access by exploring the local emulator on this address.

https://localhost:8081/_explorer/index.html and you should see a screen as follows.

Step 5:

Once you verify your Azure Cosmos DB Emulator is running, you can go back to Visual Studio Code and try to attach the emulator by selecting Connected with Azure Cosmos DB Emulator option

After 1 or 2 minutes, you can find your local Cosmos DB data also mapped in Visual Studio Code.

As a developer I found this extension is very powerful and if you are developing Azure based solution with Visual Studio code, you must start exploring this.

Start building application with cosmosdb today 😊 Cheers!