{"record":{"id":"3f301d6e90f130c5","repo":"JamesNK/Newtonsoft.Json","slug":"could-not-determine-json-object-type-for-type-0","errorCode":null,"errorMessage":"Could not determine JSON object type for type {0}.","messagePattern":"Could not determine JSON object type for type (.+?)\\.","errorType":"exception","errorClass":"ArgumentException","httpStatus":null,"severity":"error","filePath":"Src/Newtonsoft.Json/Linq/JContainer.cs","lineNumber":774,"sourceCode":"                return;\n            }\n\n            ValidateContent(content);\n            MergeItem(content, settings);\n        }\n\n        private void ValidateContent(object content)\n        {\n            if (content.GetType().IsSubclassOf(typeof(JToken)))\n            {\n                return;\n            }\n            if (IsMultiContent(content))\n            {\n                return;\n            }\n\n            throw new ArgumentException(\"Could not determine JSON object type for type {0}.\".FormatWith(CultureInfo.InvariantCulture, content.GetType()), nameof(content));\n        }\n\n        internal void ReadTokenFrom(JsonReader reader, JsonLoadSettings? options)\n        {\n            int startDepth = reader.Depth;\n\n            if (!reader.Read())\n            {\n                throw JsonReaderException.Create(reader, \"Error reading {0} from JsonReader.\".FormatWith(CultureInfo.InvariantCulture, GetType().Name));\n            }\n\n            ReadContentFrom(reader, options);\n\n            int endDepth = reader.Depth;\n\n            if (endDepth > startDepth)\n            {\n                throw JsonReaderException.Create(reader, \"Unexpected end of content while loading {0}.\".FormatWith(CultureInfo.InvariantCulture, GetType().Name));","sourceCodeStart":756,"sourceCodeEnd":792,"githubUrl":"https://github.com/JamesNK/Newtonsoft.Json/blob/4f73e74372445108d2c1bda37b36e6f5e43402e0/Src/Newtonsoft.Json/Linq/JContainer.cs#L756-L792","documentation":"ValidateContent (invoked by Merge) throws ArgumentException when the content is neither a JToken subclass nor multi-content (an IEnumerable that is not string, JToken, or byte[]). Merge can only combine JSON tokens or enumerables of them.","triggerScenarios":"jObject.Merge(42); jArray.Merge(new DateTime()); Merge(someRandomPoco) where the poco is not a JToken or IEnumerable.","commonSituations":"Assuming Merge accepts arbitrary CLR objects like Add/FromObject; passing a primitive or DTO directly.","solutions":["Convert the value first: Merge(JToken.FromObject(poco)) or Merge(new JValue(42)).","For collections of CLR objects, project to JTokens (e.g. items.Select(JToken.FromObject)) before merging.","Use JsonConvert serialization then JToken.Parse if you need full serializer behavior."],"exampleFix":"// before\njObject.Merge(myPoco);\n// after\njObject.Merge(JToken.FromObject(myPoco));","handlingStrategy":"validation","validationCode":"object safe = content;\nif (!(content is JToken) && !IsMultiContent(content)) {\n    safe = JToken.FromObject(content);\n}\ncontainer.Merge(safe);\n\nstatic bool IsMultiContent(object o) =>\n    o is System.Collections.IEnumerable && !(o is string) && !(o is byte[]) && !(o is JToken);","typeGuard":"static bool IsMergeable(object o) =>\n    o is JToken || (o is System.Collections.IEnumerable && !(o is string) && !(o is byte[]));","tryCatchPattern":"try { container.Merge(content); }\ncatch (ArgumentException ex) when (ex.Message.Contains(\"Could not determine JSON object type\")) {\n    container.Merge(JToken.FromObject(content));\n}","preventionTips":["Convert CLR objects to JToken (JToken.FromObject) before Merge.","Pass JToken or IEnumerable<JToken> only.","Use Merge on the result of JToken.Parse/FromObject, not raw DTOs."],"tags":["jcontainer","merge","validate","argument"],"analyzedSha":"4f73e74372445108d2c1bda37b36e6f5e43402e0","analyzedAt":"2026-08-07T06:10:08.596Z","schemaVersion":2},"datasetVersion":"2026-08-07T07:17:06.508Z"}