We’ve been migrating a classic WebApi application into the ASP.NET Core API for quite a while now, and last week we decided to deploy it on the test environment and try to run a website against it. We were pretty confident about the quality of a migration because all of the integration tests from old API were green when running against a new one. We were expecting maybe some business logic bugs but from our perspective, the infrastructure part was good to go. Unfortunately, when the QA’s run the selenium test suite they quickly found a major issue in our codebase. They basically were getting HTTP 500 errors indicating a NullReferenceException. That was pretty surprising to us and after a bit of a digging we found following lines in the logs
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TimeStamp=2017-08-20 00:43:49.4383 TraceId=0HL77AF0N305P Level=DEBUG Message=JSON input formatter threw an exception. Newtonsoft.Json.JsonSerializationException: Error converting value {null} to type 'System.Int32'. Path 'PassengerNumber', line 2, position 26. ---> System.InvalidCastException: Null object cannot be converted to a value type. at System.Convert.ChangeType(Object value, Type conversionType, IFormatProvider provider) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType) --- End of inner exception stack trace --- at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.EnsureType(JsonReader reader, Object value, CultureInfo culture, JsonContract contract, Type targetType) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.CreateValueInternal(JsonReader reader, Type objectType, JsonContract contract, JsonProperty member, JsonContainerContract containerContract, JsonProperty containerMember, Object existingValue) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.SetPropertyValue(JsonProperty property, JsonConverter propertyConverter, JsonContainerContract containerContract, JsonProperty containerProperty, JsonReader reader, Object target) at Newtonsoft.Json.Serialization.JsonSerializerInternalReader.PopulateObject(Object newObject, JsonReader reader, JsonObjectContract contract, JsonProperty member, String id) |
this was resulting in a null request in controller’s action
As you can see JSON serializer was not able to convert null into the int. We double checked the requests coming from front-end and this is how one of them looked like
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{ "PassengerNumber": null, "PassengerType": "2" } |
whereas corresponding request class on the server side was written in following way
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public class CreatePassengerRequest { public int PassengerNumber { get; set; } public int PassengerType { get; set; } } |
Clearly front-end shouldn’t be sending a null as a PassengerNumber however the same request was serialized just fine when running against classic WebApi
Fortunately the fix for that was pretty straightforward. All we had to do was to configure JSON serializer to ignore null values.
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// This method gets called by the runtime. Use this method to add services to the container. public void ConfigureServices(IServiceCollection services) { services.AddMvc().AddJsonOptions(options => { options.SerializerSettings.NullValueHandling = NullValueHandling.Ignore; }); } |
From now on we were able to properly serialize the request
Source code for this post can be found here
so useful thanks.
Good job!
Thank you for sharing