Golang json unknown fields Anonymous structs can help keep API handlers clean and simple. Today we are going to explore marshaling JSON using anonymous structs. When unmarshaling a number into an interface value, it is unmarshaled as an int64 if the JSON data does not contain a ". Unmarshal function. Unlike structs, which require predefined fields, maps allow you to store key-value pairs without knowing the structure in advance. What Is A Struct? | Go’s structs are typed collections of fields. mapstructure works mostly like JSON unmarshalling: type Params struct { Name string `mapstructure:"name"` Domain string `mapstructure:"domain"` Version string `mapstructure:"version"` Deployer string `mapstructure Jun 27, 2017 · 8 This question already has answers here: Unmarshal JSON with some known, and some unknown field names (9 answers) Jul 24, 2018 · Raise an Error in Go when Unmarshalling Unknown Fields from JSON (with exceptions) I want an Error to be raised during JSON unmarshalling if an undetected field is found. They’re useful for grouping data together to form records Oct 8, 2021 · So I thought originally to change the JSON to "password" for struct field Password but that throws an internal server error: illegal base64 data at input byte 4 Jul 30, 2025 · When unmarshaling into a struct, JSON keys must case-sensitively match `json` tag names (for tagged struct fields) or struct field names (for untagged struct fields), or they are treated as unknown fields and discarded. I unmarshall the JSON into a map, check the type/kind field in the map then decode the map into the appropriate struct. Does that work for nested fields too? So if a known field is a struct and a json for that field contains an unknown (sub-)field, would that be in the catch-all map too? Nov 27, 2024 · The Go JSON Package Go provides extensive support for JSON encoding and decoding with the encoding/json package. If this behavior is undesirable, check out the next section. ". How to handle missing fields, and leave out struct fields when marshalling and unmarshalling JSON in Go. Dec 4, 2013 · An anonymous struct field with a name given in its JSON tag is treated as having that name, rather than being anonymous. To deserialize JSON data into Go structs, you can use the json. Anonymous structures are unnamed, temporary structures used for a one-time purpose, while anonymous fields allow embedding fields without names. JSON is a result of POST request. Jun 22, 2024 · This section delves into the complexities of optional fields, handling unknown JSON fields, and custom type encoding and decoding, ensuring comprehensive and flexible JSON processing in your Go applications. For example, if the JSON didn't have the level field at all, the Options struct unmarshaled from it would have 0 for Level. Handling of anonymous struct fields is new in Go 1. Example: Nov 5, 2025 · An anonymous struct field with a name given in its JSON tag is treated as having that name, rather than being anonymous. consuming 'unknown' JSON fields So far when ive worked with webservices in golang i would strong type the JSON fields that are neccesary and thats been fine as ive mostly had control over the callers. Jan 10, 2023 · It doesn't work because you did the mistake that is asked twice a week on SO and explained in any totorial or documentation about json marshaling in Go. May 23, 2020 · For (1), Go's json package will assign values only to fields found in the JSON; other fields will just keep their Go zero values. Mar 19, 2018 · Is it possible to unmarshal JSON with unknown field? That field name is always different, but the structure is the same. 1. In the discussion of that propos Nov 5, 2024 · In Golang, structures (or structs) allow us to group elements of various types into a single unit, which is useful for modeling real-world entities. But what happens if your JSON data contains fields that don't exist in your Go struct? Ignoring Unknown Fields The simplest way to handle unknown fields is to ensure they’re ignored during the In Go, the map type is a powerful tool for handling dynamic JSON structures. Apr 21, 2020 · Go is a language built for the web. The UnmarshalJSON method allows us to inspect the JSON token stream and decide how to unmarshal the JSON payload. The Go standard library comes with everything we need to stand up a production web server. Nov 1, 2017 · Yesterday I've implemented #15314, which allows to optionally fail JSON decoding if an object has a key which cannot be mapped to a field in the destination struct. I've done something similar to this by using mapstructure. For example, consider a JSON response from an API that returns different fields based on the request: Oct 9, 2024 · Detecting null, set, and missing JSON fields with Go We can use custom unmarshalling logic by implementing the Unmarshaler interface to detect the difference between null and missing fields. This flexibility makes maps ideal for working with JSON data that can vary in structure. An anonymous struct field of interface type is treated the same as having that type as its name, rather than being anonymous. Jul 24, 2018 · Raise an Error in Go when Unmarshalling Unknown Fields from JSON (with exceptions) I want an Error to be raised during JSON unmarshalling if an undetected field is found. usyxv jxhz ghyi nrggj mcsgeu wme yiqj zjjaue xrlwvj bkmib dtmtwv ttzf gjmccs njzwtv wis