DynamoDb, Reading and Writing Data with .Net Core – Part 2

Aug 6, 2020 # dotNet Core 3.1, DynamoDb, AspNet, AWS

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Full source code available here.

A few weeks ago I posted about reading and writing data to DynamoDb. I gave instructions on how to get create tables on localstack and how to use the AWS Document Model approach. I also pointed out that I was not a big fan of this, reading data looks like –

1[HttpGet("{personId}")]
2public async Task<IActionResult> Get(int personId)
3{
4    Table people = Table.LoadTable(_amazonDynamoDbClient, "People");
5    var person = JsonSerializer.Deserialize<Person> ((await people.GetItemAsync(personId)).ToJson());
6    return Ok(person);
7}

You have to cast to Json, then deserialize, I think you should be able to do something more like – people.GetItemAsync(personId), but you can’t

And writing data looked like –

 1[HttpPost]
 2public async Task<IActionResult> Post(Person person)
 3{
 4    Table people = Table.LoadTable(_amazonDynamoDbClient, "People");
 5     
 6    var document = new Document();
 7    document["PersonId"] = person.PersonId;
 8    document["State"] = person.State;
 9    document["FirstName"] = person.FirstName;
10    document["LastName"] = person.LastName;
11    await people.PutItemAsync(document);
12     
13    return Created("", document.ToJson());
14}

For me this feels even worse, having to name the keys in the document, very error prone.

Luckily there is another approach that is a little better. You have to create a class with attributes that indicate what table the class represents, and what properties represent the keys in the table.

 1using Amazon.DynamoDBv2.DataModel;
 2 
 3namespace DynamoDbApiObjectApproach.Models
 4{
 5     
 6    [DynamoDBTable("People")]
 7    public class PersonDynamoDb
 8    {
 9 
10        [DynamoDBHashKey]
11        public int PersonId {get;set;}
12        public string State {get;set;}
13        public string FirstName {get;set;}
14        public string LastName {get;set;}
15    }
16}

Because of these attributes, I don’t want to expose this class too broadly, so I create a simple POCO to represent a person.

1public class Person
2{
3    public int PersonId {get;set;}
4    public string State {get;set;}
5    public string FirstName {get;set;}
6    public string LastName {get;set;}
7}

I use AutoMapper to map between the two classes, never exposing the PersonDynamoDb to the outside world. If you need help getting started with AutoMapper I wrote a couple of posts on this recently.

Here’s how reading and writing looks now –

 1[HttpGet("{personId}")]
 2public async Task<IActionResult> Get(int personId)
 3{
 4    var personDynamoDb = await _dynamoDBContext.LoadAsync<PersonDynamoDb>(personId);
 5    var person = _mapper.Map<Person>(personDynamoDb);
 6    return Ok(person);
 7}
 8 
 9[HttpPost]
10public async Task<IActionResult> Post(Person person)
11{
12    var personDynamoDb = _mapper.Map<PersonDynamoDb>(person);
13    await _dynamoDBContext.SaveAsync(personDynamoDb);
14    return Created("", person.PersonId);
15}

This is an improvement, but still not thrilled with the .NET SDK for DynamoDb.

Full source code available here.

dotNet Core 3.1 DynamoDb AspNet AWS

DynamoDb, Reading and Writing Data with .Net Core – Part 2

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