#CASBAN6: Implementing the API endpoints with Azure Functions

After my last post, we have the base implementation ready to be used for our endpoints. As we already know, our endpoints will feature the CRUD pattern to interact with the endpoints. Please note: the code on GitHub is already a few steps ahead and may look a bit different from what I am posting here (mostly due to the OpenApi attributes, but you will be able to follow along).

I will use the AuthorFunction to demonstrate the implementation. All other function implementations besides the BlogFunction follow the same pattern.

Let’s dive in

First, we create a new class that derives from our base class. The constructor initializes the EF context as well as the ILogger for the author function. On top, we are defining the Route template that our functions are going to use as constant, so we can refer it in the function’s attributes. You should now have something similar to this:

 public class AuthorFunction : BlogFunctionBase
{
    private const string Route = "blog/{blogId}/author";

    public AuthorFunction(BlogContext blogContext, ILoggerFactory loggerFactory) : base(blogContext) =>
        Logger = loggerFactory.CreateLogger<AuthorFunction>();
}

Override the Create method

The Create function is obviously responsible for creating a new entry in our database. First, we check if the blogId query parameter was specified and if it is parsable as a Guid. This step is the same for all endpoints. If these checks succeed, we are moving on to the next step, in this case deserializing the submitted Author DTO.

We are using then the CreateFrom mapping extension method to transform the DTO into the EntityModel.Author object (read my post on DTOs and mappings here). The latter one can then be added to the context’s authors list and saved. If all goes well, we create a 201 Created response indicating the direct API url to read the newly created author. In all other cases, we have some error handling in place.

 [Function($"{nameof(AuthorFunction)}_{nameof(Create)}")]
public override async Task<HttpResponseData> Create([HttpTrigger(AuthorizationLevel.Anonymous, "post", Route = Route)] HttpRequestData req, string blogId)
{
    try
    {
        if (string.IsNullOrWhiteSpace(blogId) || Guid.Parse(blogId) == default)
            return await req.CreateResponseDataAsync(HttpStatusCode.BadRequest, "Required parameter 'blogId' (GUID) is not specified or cannot be parsed.");


        string requestBody = await new StreamReader(req.Body).ReadToEndAsync();

        Author? author = JsonConvert.DeserializeObject<Author>(requestBody);

        if (author != null)
        {

            EntityModel.Author? newAuthorEntity = author.CreateFrom(Guid.Parse(blogId));

            EntityEntry<EntityModel.Author> createdAuthor =
                BlogContext.Authors.Add(newAuthorEntity);

            await BlogContext.SaveChangesAsync();

            return await req.CreateNewEntityCreatedResponseDataAsync(createdAuthor.Entity.AuthorId);
        }
        else
        {
            return await req.CreateResponseDataAsync(HttpStatusCode.BadRequest, "Submitted data is invalid, author cannot be created.");
        }
    }
    catch (Exception ex)
    {
        Logger.LogError(ex, "Error creating author object on blog with Id {BlogId}", blogId);
        return await req.CreateResponseDataAsync(HttpStatusCode.InternalServerError, "An internal server error occured. Error details logged.");
    }
}

Override the GetList method

We are using the GetList method to retrieve a list of entities. This method employs also the count and skip parameters, which is a simple way of implementing paging. We are using the ToDto method on the EnityModel.Author list to return the entities to the caller.

If something is going wrong during the function call, we have some error handling in place.

 [Function($"{nameof(AuthorFunction)}_{nameof(GetList)}")]
public override async Task<HttpResponseData> GetList([HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = Route)] HttpRequestData req, string blogId)
{
    try
    {
        Logger.LogInformation("Trying to get authors...");

        if (string.IsNullOrWhiteSpace(blogId) || Guid.Parse(blogId) == default)
            return await req.CreateResponseDataAsync(HttpStatusCode.BadRequest, "Required parameter 'blogId' (GUID) is not specified or cannot be parsed.");

        (int count, int skip) = req.GetPagingProperties();

        List<EntityModel.Author> entityResultSet = await BlogContext.Authors.
                                                                     Include(author => author.UserImage).
                                                                     ThenInclude(media => media.MediumType).
                                                                     Where(author => author.BlogId == Guid.Parse(blogId)).
                                                                     Skip(skip).
                                                                     Take(count).
                                                                     ToListAsync();

        List<Author> resultSet = entityResultSet.Select(entity => entity.ToDto()).ToList();

        return await req.CreateOkResponseDataWithJsonAsync(resultSet, JsonSerializerSettings);
    }
    catch (Exception ex)
    {
        Logger.LogError(ex, "Error getting author list for blog with Id \'{Id}\'", blogId);
        return await req.CreateResponseDataAsync(HttpStatusCode.InternalServerError, "An internal server error occured. Error details logged.");
    }
}

Override the GetSingle method

The GetSingle endpoint needs also the id of the desired entity to be executed. This call is for getting just a single author from the database. Also here we have our error handling in place.

 [Function($"{nameof(AuthorFunction)}_{nameof(GetSingle)}")]
public override async Task<HttpResponseData> GetSingle([HttpTrigger(AuthorizationLevel.Anonymous, "get", Route = Route + "/{id}")] HttpRequestData req, string blogId, string id)
{
    try
    {
        if (string.IsNullOrWhiteSpace(blogId) || Guid.Parse(blogId) == default)
            return await req.CreateResponseDataAsync(HttpStatusCode.BadRequest, "Required parameter 'blogId' (GUID) is not specified or cannot be parsed.");
        
        if (!string.IsNullOrWhiteSpace(id))
        {
            Logger.LogInformation("Trying to get author with Id: {Id}...", id);

            EntityModel.Author? existingAuthor =
                await BlogContext.Authors.
                                  Include(author => author.UserImage).
                                  ThenInclude(media => media.MediumType).
                                  SingleOrDefaultAsync(author => author.BlogId == Guid.Parse(blogId) &&
                                                                 author.AuthorId == Guid.Parse(id));

            if (existingAuthor == null)
            {
                Logger.LogWarning("Author with Id {Id} not found", id);
                return req.CreateResponse(HttpStatusCode.NotFound);
            }

            return await req.CreateOkResponseDataWithJsonAsync(existingAuthor.ToDto(), JsonSerializerSettings);
        }
        else
        {
            return await req.CreateResponseDataAsync(HttpStatusCode.BadRequest, "Submitted data is invalid, must specify BlogId");
        }
    }
    catch (Exception ex)
    {
        Logger.LogError(ex, "Error getting author with Id '{AuthorId}' for blog with Id \'{BlogId}\'", id, blogId);
        return await req.CreateResponseDataAsync(HttpStatusCode.InternalServerError, "An internal server error occured. Error details logged.");
    }
}

Override the Update method

The structure of the Update function should be no surprise. First check the blog’s id, then read the submitted Author DTO. If the author already exists, update the information of the Author in the database. Otherwise, tell the caller there is no such author.

 [Function($"{nameof(AuthorFunction)}_{nameof(Update)}")]
public override async Task<HttpResponseData> Update([HttpTrigger(AuthorizationLevel.Anonymous, "put", Route = Route + "/{id}")] HttpRequestData req, string blogId, string id)
{
    try
    {
        if (string.IsNullOrWhiteSpace(blogId) || Guid.Parse(blogId) == default)
            return await req.CreateResponseDataAsync(HttpStatusCode.BadRequest, "Required parameter 'blogId' (GUID) is not specified or cannot be parsed.");

        string requestBody = await new StreamReader(req.Body).ReadToEndAsync();

        Author? authorToUpdate = JsonConvert.DeserializeObject<Author>(requestBody);

        if (authorToUpdate != null)
        {
            EntityModel.Author? existingAuthor =
                await BlogContext.Authors.
                                  Include(author => author.UserImage).
                                  ThenInclude(media => media.MediumType).
                                  SingleOrDefaultAsync(author => author.BlogId == Guid.Parse(blogId) &&
                                                                 author.AuthorId == Guid.Parse(id));

            if (existingAuthor == null)
            {
                Logger.LogWarning("Author with Id {Id} not found", id);
                return req.CreateResponse(HttpStatusCode.NotFound);
            }

            existingAuthor.UpdateWith(authorToUpdate);

            await BlogContext.SaveChangesAsync();

            return req.CreateResponse(HttpStatusCode.Accepted);
        }
        else
        {
            return await req.CreateResponseDataAsync(HttpStatusCode.BadRequest, "Submitted data is invalid, author cannot be modified.");
        }
    }
    catch (Exception ex)
    {
        Logger.LogError(ex, "Error updating author with Id '{AuthorId}' for blog with Id \'{BlogId}\'", id, blogId);
        return await req.CreateResponseDataAsync(HttpStatusCode.InternalServerError, "An internal server error occured. Error details logged.");
    }
}

Override the Delete method

Last but not least, we sometimes need to delete entities for whatever reason. This is where the Delete function comes into play. This function requires both the blog’s id and the entity’s id to be executed. As with all other functions, there is some error handling in place.

 [Function($"{nameof(AuthorFunction)}_{nameof(Delete)}")]
public override async Task<HttpResponseData> Delete([HttpTrigger(AuthorizationLevel.Anonymous, "delete", Route = Route + "/{id}")] HttpRequestData req, string blogId, string id)
{
    try
    {
        if (string.IsNullOrWhiteSpace(blogId) || Guid.Parse(blogId) == default)
            return await req.CreateResponseDataAsync(HttpStatusCode.BadRequest, "Required parameter 'blogId' (GUID) is not specified or cannot be parsed.");

        EntityModel.Author? existingAuthor = await BlogContext.Authors.
                                                               Include(author => author.UserImage).
                                                               SingleOrDefaultAsync(author => author.BlogId == Guid.Parse(blogId) &&
                                                                                              author.AuthorId == Guid.Parse(id));

        if (existingAuthor == null)
        {
            Logger.LogWarning("Author with Id {Id} not found", id);
            return req.CreateResponse(HttpStatusCode.NotFound);
        }

        BlogContext.Authors.Remove(existingAuthor);

        await BlogContext.SaveChangesAsync();

        return req.CreateResponse(HttpStatusCode.OK);
    }
    catch (Exception ex)
    {
        Logger.LogError(ex, "Error deleting author with Id '{AuthorId}' from blog with Id \'{BlogId}\'", id, blogId);
        return await req.CreateResponseDataAsync(HttpStatusCode.InternalServerError, "An internal server error occured. Error details logged.");
    }
}

Helper methods

You might have noticed that there are some extensions methods in the code samples above you haven’t seen so far. I got you, here they are.

Paging properties

To get the paging properties (I use simple paging here), we have the query parameters count and skip. To extract them from the request, we do some parsing on the parameters that the HttpRequestData provides us.

 private static Dictionary<string, string> GetQueryParameterDictionary(this HttpRequestData req)
{
    Dictionary<string, string> result = new Dictionary<string, string>();

    string queryParams = req.Url.GetComponents(UriComponents.Query, UriFormat.UriEscaped);

    if (!string.IsNullOrWhiteSpace(queryParams))
    {
        string[] paramSplits = queryParams.Split('&');

        if (paramSplits.Any())
        {
            foreach (string split in paramSplits)
            {
                string[] valueSplits = split.Split('=');

                if (valueSplits.Any() && valueSplits.Length == 2)
                    result.Add(valueSplits[0], valueSplits[1]);
            }
        }
    }
    return result;
}

public static (int count, int skip) GetPagingProperties(this HttpRequestData req)
{
    Dictionary<string, string> queryParams = req.GetQueryParameterDictionary();

    int count = 10;
    int skip = 0;

    if (queryParams.Any(p => p.Key == nameof(count)))
        _ = int.TryParse(queryParams[nameof(count)], out count);

    if (queryParams.Any(p => p.Key == nameof(skip)))
        _ = int.TryParse(queryParams[nameof(skip)], out skip);

    return (count, skip);
}

HttpResponseData helpers

Our function will run in an isolated process. Besides having a bunch of advantages like easier dependency injection, it brings also some syntax changes. As you can see from the docs, we are now responding with a HttpResponseData object. For easier creation of these objects, I wrote these extensions:

 public static async Task<HttpResponseData> CreateResponseDataAsync(this HttpRequestData req, HttpStatusCode statusCode, string? message)
{
    HttpResponseData response = req.CreateResponse(statusCode);

    if (string.IsNullOrWhiteSpace(message))
        message = statusCode.ToString();

    await response.WriteStringAsync(message);

    return response;
}

public static async Task<HttpResponseData> CreateNewEntityCreatedResponseDataAsync(this HttpRequestData req, Guid createdResourceId)
{
    HttpResponseData response = req.CreateResponse(HttpStatusCode.Created);
    response.Headers.Add("Location", $"{req.Url}/{createdResourceId}");

    await response.WriteStringAsync("OK");

    return response;
}

public static async Task<HttpResponseData> CreateOkResponseDataWithJsonAsync(this HttpRequestData req, object responseData, JsonSerializerSettings? settings)
{
    string json = JsonConvert.SerializeObject(responseData, settings);
    
    HttpResponseData response = req.CreateResponse(HttpStatusCode.OK);
    response.Headers.Add("Content-Type", "application/json; charset=utf-8");

    await response.WriteStringAsync(json);

    return response;
}

The first one creates a response with the specified HttpStatusCode and an optional message. The second one is for the 201 Created responses, while the last one is for the 200 OK responses.

The BlogFunction

The BlogFunction implmentation is the only one not deriving from the base class. As the blog is the root entity, there are some differences from the pattern above.

The Create method in this function works without the blog’s id, but otherwise is the same as for all other Create methods.

The GetBlogList method features count properties for its child entities (authors, posts, tags, media) and does also not need the blog’s id. Details of child entities should be loaded via their function implementations.

The GetBlog method tries to load a blog completely with all child entities. This may result in a very large data set and should be used with caution and for exports only.

The Update and Delete methods are once again following the pattern of the other functions, except they just need the blog’s id.

You can have a look at the BlogFunction right here on GtiHub.

Anonymous authorization

If you are wondering why all the functions have the AuthorizationLevel set to Anonymous, I got you. Once the function is deployed to Azure, we will use the Azure Active Directory to force a login to a Microsoft account (others may follow) to call our functions. We have a strong protection this way without big efforts.

Conclusion

In this post, I showed you how to use the base class we created in the last post of the series, and also showed you how the BlogFunction differs from that. In the next post, we will have a look at how to add Swagger to our Functions that will make API testing a lot easier as we advance with our project. With each post, we are getting closer to deploy the API functions to Azure, so stay tuned for the next post(s)!

Until the next post, happy coding, everyone!