Tag Archives: JsonPatchDocument

.NET Core web API + Dapper – HTTP Patch

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The application I’m currently working on has some tables with many columns and these were proving painful to update with HTTP PUT methods. Over the last couple of releases, I have been extending the customer facing API with PATCH methods so the client can specify only the values to changed. 

{ 
    "op": "replace", 
    "path": "/name", 
    "value": "USB missile launcher (Green)." 
},
{ 
    "op": "replace", 
    "path": "/UnitPrice", 
    "value": 25
},
{ 
    "op": "replace", 
    "path": "/recommendedRetailPrice", 
    "value": 37.41
}

The JSON Patch is a format for specifying updates to be applied to a resource.

Stock Items list before HTTP Patch operation

A JSON Patch document has an array of operations which identify a particular type of change.

Using Telerik Fiddler Composer functionality to apply an HTTP PATCH
Stock Items list after HTTP Patch operation

The StockItemPatchDtoV1 class is decorated with DataAnnotations to ensure the contents are valid.

public class StockItemPatchDtoV1
{
    [Required]
    [StringLength(100, MinimumLength = 1, ErrorMessage = "The name text must be at least {2} and no more than {1} characters long")]  // These would be constants in a real application
    public string Name { get; set; }

    [Required]
    [Range(0.0, 100.0)] // These would be constants in a real application
    public decimal UnitPrice { get; set; }

    [Required]
    [Range(0.0, 1000000.0)] // These would be constants in a real application
    public decimal RecommendedRetailPrice { get; set; }
}

The StockItemsController [HttpPatch(“{id}”)] method retrieves the stock item to be updated, then uses ApplyTo method and TryValidateModel to update only the specified fields.

[HttpPatch("{id}")]
public async Task<ActionResult<Model.StockItemGetDtoV1>> Patch([FromBody] JsonPatchDocument<Model.StockItemPatchDtoV1> stockItemPatch, int id)
{
    Model.StockItemGetDtoV1 stockItem;

    using (IDbConnection db = dapperContext.ConnectionCreate())
    {
        stockItem = await db.QuerySingleOrDefaultWithRetryAsync<Model.StockItemGetDtoV1>(sql: "[Warehouse].[StockItemsStockItemLookupV1]", param: new { stockItemId = id }, commandType: CommandType.StoredProcedure);

        if (stockItem == default)
        {
            logger.LogInformation("StockItem:{id} not found", id);

            return this.NotFound($"StockItem:{id} not found");
        }

        Model.StockItemPatchDtoV1 stockItemPatchDto = mapper.Map<Model.StockItemPatchDtoV1>(stockItem);

        stockItemPatch.ApplyTo(stockItemPatchDto, ModelState);

        if (!ModelState.IsValid || !TryValidateModel(stockItemPatchDto))
        {
            logger.LogInformation("stockItemPatchDto invalid {0}", string.Join(Environment.NewLine, ModelState.Values.SelectMany(v => v.Errors).Select(v => v.ErrorMessage + " " + v.Exception))); // would extract this out into shared module

            return BadRequest(ModelState);
        }

        mapper.Map(stockItemPatchDto, stockItem);

        await db.ExecuteWithRetryAsync(sql: "UPDATE Warehouse.StockItems SET StockItemName=@Name, UnitPrice=@UnitPrice, RecommendedRetailPrice=@RecommendedRetailPrice WHERE StockItemId=@Id", param: stockItem, commandType: CommandType.Text);
    }

    return this.Ok();
}

Initially the HTTP Patch method returned this error message.

HTTP/1.1 400 Bad Request
Content-Type: application/problem+json; charset=utf-8
Date: Tue, 27 Jun 2023 09:20:30 GMT
Server: Kestrel
Transfer-Encoding: chunked

1d7
{"type":"https://tools.ietf.org/html/rfc7231#section-6.5.1","title":"One or more validation errors occurred.","status":400,"traceId":"00-665a6ee9ed1105a105237c421793af5d-1719bda40c0b7d5d-00","errors":{"$":["The JSON value could not be converted to Microsoft.AspNetCore.JsonPatch.JsonPatchDocument`1[devMobile.WebAPIDapper.HttpPatch.Model.StockItemPatchDtoV1]. Path: $ | LineNumber: 0 | BytePositionInLine: 1."],"stockItemPatch":["The stockItemPatch field is required."]}}
0

After some research I worked out that I had forgotten to wire up the Newtonsoft JSON support with builder.Services.AddControllers().AddNewtonsoftJson();