How to use Patch method in minimal api application? - asp.net-core

Question

I am trying to use patch method in my minimal api application this is my code :
Car class
public class Car
{
[JsonProperty(PropertyName = "id")]
public string Id { get; set; }
[JsonProperty(PropertyName = "producent")]
public Producent Producent { get; set; }
[JsonProperty(PropertyName = "age")]
public int Age { get; set; }
[JsonProperty(PropertyName = "yearCreated")]
public int YearCreated { get; set; }
[JsonProperty(PropertyName = "engine")]
public Engine Engine { get; set; }
public Car()
{
Id= Guid.NewGuid().ToString();
YearCreated = DateTime.Now.Year - Age;
}
}
ICarService:
public interface ICarService
{
Task<IEnumerable<Car>> GetAll();
Task<Car> GetById(string id,string partitionKey);
Task Create(Car car);
Task<bool> Update(Car car);
Task<Car> UpdatePatchAsync(string id, string partitionKey,List<PatchOperation> patchOperations);
Task<bool> Delete(string id,string partitionKey);
}
patch method in service
public async Task<Car> UpdatePatchAsync(string id, string partitionKey, List<PatchOperation> patchOperations)
{
var result = await _container.PatchItemAsync<Car>(id, new PartitionKey(partitionKey),
patchOperations:patchOperations );
return result;
}
my requests:
[HttpPatch]
public static async Task<IResult> Patch(ICarService service,string id,string partitionKey,
[FromBody]List<PatchOperation> operations)
{
var updatedCar = await service.UpdatePatchAsync(id,partitionKey,operations);
if (updatedCar == null)
{
return Results.NotFound();
}
return Results.Ok(updatedCar);
}
app.MapMethods("/cars/patch/{id}/{partitionKey}", new string[] { "PATCH" }, CarRequests.Patch);
I use cosmosDb database and when i code like this:
{
"op": "replace",
"path": "age",
"value": 22
}
i get the error
System.NotSupportedException: Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported. Type 'Microsoft.Azure.Cosmos.PatchOperation'. Path: $[0] | LineNumber: 3 | BytePositionInLine: 3.
---> System.NotSupportedException: Deserialization of types without a parameterless constructor, a singular parameterized constructor, or a parameterized constructor annotated with 'JsonConstructorAttribute' is not supported. Type 'Microsoft.Azure.Cosmos.PatchOperation'.

Answer 1

The problem is you are using [FromBody]List<PatchOperation> operations.
This is making ASP.NET attempt to deserialize a JSON raw string into PatchOperation, which when we look at our source code, has no parameterless constructor: https://github.com/Azure/azure-cosmos-dotnet-v3/blob/master/Microsoft.Azure.Cosmos/src/Patch/PatchOperation.cs, it is an abstract class.
The way it is meant to be used is through PatchOperation.XXXX, like PatchOperation.Add, you cannot use it to deserialize into it. You could have your own MyPatchOperation<Car> that has the exposed properties for deserialization, and then simply have a method in that class that based on which properties are populated, calls PatchOperation<Car>.Add (or whatever operation).
Not the full code but:
public class MyPatchOperation
{
[JsonProperty(PropertyName = "op")]
public string Operation { get; set; }
[JsonProperty(PropertyName = "path")]
public string Path { get; set; }
[JsonProperty(PropertyName = "value")]
public string Value { get; set; }
public PatchOperation<Car> ToPatchOperation()
{
switch (this.Operation)
{
case "replace":
return PatchOperation<Car>.Replace(this.Path, this.Value);
/* other operations */
}
}
}