Add readme

README.md

@@ -0,0 +1,118 @@
+Usage example with a repository pattern:
+
+```csharp
+using System.Net;
+using Amazon.DynamoDBv2;
+using Amazon.DynamoDBv2.DataModel;
+using Amazon.DynamoDBv2.Model;
+using DynamoDBGenerator.Attributes;
+using Dynatello;
+using Dynatello.Builders;
+using Dynatello.Builders.Types;
+
+ProductRepository productRepository = new ProductRepository("MY_TABLE", new AmazonDynamoDBClient());
+
+public class ProductRepository
+{
+    private readonly IAmazonDynamoDB _amazonDynamoDb;
+    private readonly GetRequestBuilder<string> _getProductByTable;
+    private readonly UpdateRequestBuilder<(string Id, decimal NewPrice, DateTime TimeStamp)> _updatePrice;
+    private readonly PutRequestBuilder<Product> _createProduct;
+    private readonly QueryRequestBuilder<decimal> _queryByPrice;
+
+    public ProductRepository(string tableName, IAmazonDynamoDB amazonDynamoDb)
+    {
+        _amazonDynamoDb = amazonDynamoDb;
+
+        _getProductByTable = Product.GetById
+            .OnTable(tableName)
+            .ToGetRequestBuilder(arg => arg); // Since the ArgumentType is set to string, we don't need to select a property.
+
+        _updatePrice = Product.UpdatePrice
+            .OnTable(tableName)
+            .WithUpdateExpression((db, arg) => $"SET {db.Price} = {arg.NewPrice}, {db.Metadata.ModifiedAt} = {arg.TimeStamp}") // Specify the update operation
+            .ToUpdateItemRequestBuilder((marshaller, arg) => marshaller.PartitionKey(arg.Id));
+
+        _createProduct = Product.Put
+            .OnTable(tableName)
+            .WithConditionExpression((db, arg) => $"{db.Id} <> {arg.Id}") // Ensure we don't have an existing Product in DynamoDB
+            .ToPutRequestBuilder();
+
+        _queryByPrice = Product.QueryByPrice
+                .OnTable(tableName)
+                .WithKeyConditionExpression((db, arg) => $"{db.Price} = {arg}")
+                .ToQueryRequestBuilder() 
+            with
+            {
+                IndexName = Product.PriceIndex
+            };
+    }
+
+    public async Task<IReadOnlyList<Product>> SearchByPrice(decimal price)
+    {
+        QueryRequest request = _queryByPrice.Build(price);
+        QueryResponse? response = await _amazonDynamoDb.QueryAsync(request);
+
+        if (response.HttpStatusCode is not HttpStatusCode.OK)
+            throw new Exception("...");
+
+        return response.Items
+            .Select(x => Product.QueryByPrice.Unmarshall(x))
+            .ToArray();
+    }
+
+    public async Task Create(Product product)
+    {
+        PutItemRequest request = _createProduct.Build(product);
+        PutItemResponse response = await _amazonDynamoDb.PutItemAsync(request);
+
+        if (response.HttpStatusCode is not HttpStatusCode.OK)
+            throw new Exception("...");
+    }
+
+    public async Task<Product?> GetById(string id)
+    {
+        GetItemRequest request = _getProductByTable.Build(id);
+        GetItemResponse response = await _amazonDynamoDb.GetItemAsync(request);
+
+        if (response.HttpStatusCode is HttpStatusCode.NotFound)
+            return null;
+
+        if (response.HttpStatusCode is not HttpStatusCode.OK)
+            throw new Exception("...");
+
+        Product product = Product.GetById.Unmarshall(response.Item);
+
+        return product;
+    }
+
+    public async Task<Product?> UpdatePrice(string id, decimal price)
+    {
+        UpdateItemRequest request = _updatePrice.Build((id, price, DateTime.UtcNow));
+        UpdateItemResponse response = await _amazonDynamoDb.UpdateItemAsync(request);
+
+        if (response.HttpStatusCode is not HttpStatusCode.OK)
+            return null;
+
+        Product product = Product.UpdatePrice.Unmarshall(response.Attributes);
+
+        return product;
+    }
+}
+
+[DynamoDBMarshaller(typeof(Product), PropertyName = "Put")]
+[DynamoDBMarshaller(typeof(Product), ArgumentType = typeof(string), PropertyName = "GetById")]
+[DynamoDBMarshaller(typeof(Product), ArgumentType = typeof((string Id, decimal NewPrice, DateTime TimeStamp)), PropertyName = "UpdatePrice")]
+[DynamoDBMarshaller(typeof(Product), ArgumentType = typeof(decimal), PropertyName = "QueryByPrice")]
+public partial record Product(
+    [property: DynamoDBHashKey, DynamoDBGlobalSecondaryIndexRangeKey(Product.PriceIndex)] string Id,
+    [property: DynamoDBGlobalSecondaryIndexHashKey(Product.PriceIndex)] decimal Price,
+    string Description,
+    Product.MetadataEntity Metadata
+)
+{
+    public const string PriceIndex = "PriceIndex";
+
+    public record MetadataEntity(DateTime CreatedAt, DateTime ModifiedAt);
+}
+```