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Posted 7 Jul 2020


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ASP.NET Core Web API + DynamoDB Locally

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8 Jul 2020CPOL4 min read
How to access DynamoDB locally using ASP.NET Core Web API
This is a walkthrough of accessing DynamoDB locally using ASP.NET Core Web API.


I wanted to create a commenting system for my [blog]( instead of using an existing one in order to learn how it's build. It was my friend, Paul's idea.

I needed a database to store and manage all the comments. Hence, I chose DynamoDB. I chose to create the API in Lambda using C#. All of this is done using AWS Serverless Application Model (SAM).

What's Covered

  • Create the ASP.NET Core Web API
  • Integrating with Swagger UI
  • Connecting and reading from DynamoDb locally


  • AWS account
  • C#
  • .NET Core SDK and Runtime installed (if you haven't got them, install them from the given links)
  • Java installed
  • .NET CLI

Create Project

  1. Open up terminal
  2. Check the dotnet version installed
    dotnet --version
  3. Install Lambda and serverless template
    dotnet new -i Amazon.Lambda.Templates
  4. Create a ASP.NET Core Web API using the template installed above:
    dotnet new serverless.AspNetCoreWebAPI --name CommentsAPI
  5. cd into the `src` and then project's folder:
    cd src
    cd CommentsAPI
  6. Restore all the dependencies:
    dotnet restore
  7. Run the project to make sure it's working without errors:
    dotnet run
  8. Use VS Code or any of your favourite text editor and open the project folder
  9. Notice four new files in addition to the normal files new .NET project area created.

Image 1

  • aws-lambda-tools-defaults.json - This file is read by lambda tooling by default. Your function handler is specified in this file. So, if you update the function's name, you need to update it in this file too.
  • LambdaEntryPoint - Pretty much self explanatory (file from which lambda executes your application code) when you deploy to AWS
  • LocalEntryProint - Local testing entry point when you test the application locally
  • serverless.template - SAM template file in JSON which defines insfrastructure as code.

Integrating Swagger

  1. We will be using Swagger to document our Web API and test it from the browser. Add NuGet package for Swagger
    dotnet add package Swashbuckle.AspNetCore
  2. To use it, you need to register it by adding the below code in the ConfigureServices method in `Startup.cs` file
    services.AddSwaggerGen(c => {
      c.SwaggerDoc("v1", new OpenApiInfo { Title = "Comments API", Version = "v1" });
  3. Add import of `Microsoft.OpenApi.Models` on the top of the page:
    using Microsoft.OpenApi.Models;
  4. Then, enable it by inserting the below code in the Configure method of Startup.cs file. Add the below code above the app.UseHttpsRedirection(); Otherwise, Swagger UI won't load.
    app.UseSwaggerUI(c =>
      c.SwaggerEndpoint("v1/swagger.json", "Comments");
      c.RoutePrefix = "swagger";
  5. Run the application and then click the url shown
  6. Replace index.html in the URL with swagger and press Enter
  7. If everything went well, you should see Swagger UI now

Install, Connect and Read from local DynamoDB

To connect and read from DynamoDB, we will need to install it locally first.

Install DynamoDB Locally

Follow the steps here.

Create Table

  1. Navigate to the folder where you extracted DynamoDBLocal.jar
  2. Start DynamoDB locally by running:
    java -Djava.library.path=./DynamoDBLocal_lib -jar DynamoDBLocal.jar -sharedDb

    Image 2

  3. Open another terminal tab.
  4. Run the below command to create a table:
    aws dynamodb create-table --table-name commentsTable --attribute-definitions AttributeName=id,AttributeType=S --key-schema AttributeName=id,KeyType=HASH --provisioned-throughput ReadCapacityUnits=5,WriteCapacityUnits=5 --endpoint-url=http://localhost:8000

    The above command creates a table named commentsTable in the endpoint http://localhost:8000

  5. To check the created table, run:
    aws dynamodb list-tables --endpoint-url http://localhost:8000

Connect ASP.NET Core Web API to Local DynamoDB

  • Navigate to your project folder. We will add two NuGet packages. These are essential to make a connection to DynamoDB:
    dotnet add package AWSSDK.DynamoDBv2
    dotnet add package AWSSDK.Extensions.NETCore.Setup

    AWSSDK.DynamoDBv2 - Add the sufficient support to interact with DynamoDB using AWS .NET SDK

    AWSSDK.Extensions.NETCore.Setup - has methods for configuration and registrations of AWS Services with dependency injection.

  • Now add configuration to appsettings.json. This contains configuration for local DynamoDB.
    "DynamoDb": {
      "LocalMode": true,
      "LocalServiceUrl": "http://localhost:8000"

    Now your appsettings.json should look like:

    Image 3

    In the above code, we create configuration for DynamoDB service and setting the mode to local. Then, we set the service URL to localhost and port 8000 to run locally.

  • Now we need to register Dynamo Service. In the Startup.cs file, add the below code in ConfigureServices method:
    var dynamoDbConfig = Configuration.GetSection("DynamoDb");
    var runLocalDynamoDb = dynamoDbConfig.GetValue<bool>("LocalMode");
    services.AddSingleton<IAmazonDynamoDB>(sp =>
      var clientConfig = new AmazonDynamoDBConfig 
        ServiceURL = dynamoDbConfig.GetValue<string>("LocalServiceUrl") 
        return new AmazonDynamoDBClient(clientConfig);

Code Explanation

  • var dynamoDbConfig = Configuration.GetSection("DynamoDb"); - Gets the section DynamoDb from the configuration file
  • var runLocalDynamoDb = dynamoDbConfig.GetValue<bool>("LocalMode"); - Gets the value of local mode
  • services.AddSingleton<IAmazonDynamoDB> - Register a service IAmazonDynamoDB interface which returns the actual implementation.
  • var clientConfig = new AmazonDynamoDBConfig { ServiceURL = dynamoDbConfig.GetValue<string>("LocalServiceUrl") }; - Create an AmazonDynamoDBConfig instance passing in the LocalServiceURL from appsetting.json
  • return new AmazonDynamoDBClient(clientConfig); - Return the AmazonDynamoDBClient using the configuration.

Read from DynamoDB Local

After registering IAmazonDynamoDB in our application, we are now in the position to insert it using Microsoft Dependency injection in the our Controller.

  • Delete the two controllers, S3ProxyController and ValuesController in the controllers folder
  • Right click on Controllers folder > New C# Class
  • Name the class CommentsController
  • Make sure the class is derived from ControllerBase
  • Add the below line above the class keywords:

Code Explanation

[Route("getcomments")] - Annotate the route where this controller can be accessed

[ApiController] - Denotes that this is a controller

  • Add the below code:
    private const string TableName = "commentsTable";
    private readonly IAmazonDynamoDB _amazonDynamoDb;
    public CommentsController(IAmazonDynamoDB amazonDynammoDb)
      _amazonDynamoDb = amazonDynammoDb;
    public async Task<ActionResult<string>> Get(int id)
      var request = new GetItemRequest
        TableName = TableName,
        Key = new Dictionary<string, AttributeValue>
          new AttributeValue
            S = id.ToString()
      var response = await _amazonDynamoDb.GetItemAsync(request);
      return response.Item["username"].S;
  • Now insert a record in DynamoDB by running:
    aws dynamodb put-item --table-name commentsTable --item '{"id": {"S": "1"},"username": {"S": "zain"}}' --endpoint-url http://localhost:8000
  • To check if the record has been inserted, scan tale using below command:
    aws dynamodb scan --table-name commentsTable --endpoint-url http://localhost:8000
  • You should see response something like this:

    Image 4

  • Now run the application by running dotnet run in your project folder.
  • Click on the URL.
  • After replacing index.html in with swagger, you should see the below page:

You are only seeing GET request as we have only implemented that method in our Controller.

  • Click on the GET button in blue.
  • Click Try It Out.
  • Type 1 in the id text box.
  • Click Execute.
  • You should see the response in Responses section.

You have finally done it. Congratulations!!!! Stay tuned for other methods too.


  • 7th July, 2020: Initial version


This article, along with any associated source code and files, is licensed under The Code Project Open License (CPOL)

Written By
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Comments and Discussions

Questionamazing explanation Pin
Member 1120946316-Jul-21 7:44
Member 1120946316-Jul-21 7:44 
PraiseInformative article about DynamoDB Pin
Rajeev.Bera3-Aug-20 18:35
Rajeev.Bera3-Aug-20 18:35 

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