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Jogson - JSON Mapper Library for Go

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A simple Go library to simplify working with JSON without the need to define structs.

Installation

Jogson requires Go version 1.18 or above.

To install the library use:

go get github.com/rmordechay/jogson

Create JsonObject, JsonArray or JsonMapper

For more information, see design.

From String

object, err := jogson.NewObjectFromString(jsonString)
array, err := jogson.NewArrayFromString(jsonString)
mapper, err := jogson.NewMapperFromString(jsonString)

From Bytes

object, err := jogson.NewObjectFromBytes(jsonBytes)
array, err := jogson.NewArrayFromBytes(jsonBytes)
mapper, err := jogson.NewMapperFromBytes(jsonBytes)

From Struct

object, err := jogson.NewObjectFromStruct(jsonStruct)
array, err := jogson.NewArrayFromStruct(jsonStruct)
mapper, err := jogson.NewMapperFromStruct(jsonStruct)

From File

mapper, err := jogson.NewMapperFromFile(jsonFilePath)
object, err := jogson.NewObjectFromFile(jsonFilePath)
array, err := jogson.NewArrayFromFile(jsonFilePath)

Read from JSON

Once you have an object, an array or a mapper, you can read the data easily. Consider the following JSON

jsonString := `{
    "id": "748494b8-7d6e-4cad-8065-89e758797313",
    "name": "Jason",
    "age": 43,
    "height": 1.87,
    "is_funny": false,
    "address": null,
    "birthday": "1981-10-08",
    "features": ["tall", "blue eyes", null],
    "children": {
        "Rachel": {"age": 15, "is_funny": false}, 
        "Sara":   {"age": 19, "is_funny": true}
    }
}`

Scalars

Getting scalars - string, int, etc. - is similar both for object and array and only differ in the parameter type (objects take string as key and arrays take int as index). You can get scalars by value or by reference, where the latter allows JSON null values. Nullable methods have the suffix 'N' in their names.

From Object

By value:

// string 
var name string = object.GetString("name") // Jason

// int 
var age int = object.GetInt("age") // 15

// float64 
var height float64 = object.GetFloat("height") // 1.87

// bool 
var isFunny bool = object.GetBool("is_funny") // false

By reference, which allows JSON null values (note the suffix 'N' at the end of the method names):

// string
var nameNullable *string = object.GetStringN("non-existent-key") // nil

// int
var ageNullable *int = object.GetIntN("non-existent-key") // nil

// float64
var heightNullable *float64 = object.GetFloatN("non-existent-key") // nil

// bool
var isFunnyNullable *bool = object.GetBoolN("non-existent-key") // nil

From Array

By value:

// string 
var s string = array.GetString(0)

// int 
var i int = array.GetInt(2)

// float64 
var f float64 = array.GetFloat(5)

// bool 
var b bool = array.GetBool(7)

By reference, which allows JSON null values (Note the suffix 'N' at the end of the method names):

// string
var nameNullable *string = array.GetStringN(100) // nil

// int
var ageNullable *int = array.GetIntN(100) // nil

// float64
var heightNullable *float64 = array.GetFloatN(100) // nil

// bool
var isFunnyNullable *bool = array.GetBoolN(100) // nil

Objects

// Check if a key exists
var keyExists bool = object.Contains("children")

// Check if the object is empty
var objectEmpty bool = object.IsEmpty()

// Get the object's size
var objectLen int = object.Length()

// Get object's keys
var keys []string = object.Keys()

// Get object's values
values := object.Values()

// Iterating over an object with key, value pair
children := object.GetObject("children")
for key, child := range children.Elements() {
    fmt.Println("Child name:", key)                   // Rachel, Sara
    fmt.Println(child.AsObject.GetInt("age"))         // 15, 19
    fmt.Println(child.AsObject.GetBool("is_funny"))   // false, true
}

As Maps

You can also get the object as a map of strings by scalars (string, int, etc.) Values that are JSON null will be returned as Go zero value. If you want to regard null values, call the function with the suffix N (see next section). If a null was found, LastError will be set and report a null conversion error. For more information, see error handling.

// Get the JsonObject as map of string and string
var stringMap map[string]string = object.AsStringMap()

// Get the JsonObject as map of string and int
var intMap map[string]int = object.AsIntMap()

// Get the JsonObject as map of string and float
var floatMap map[string]float64 = object.AsFloatMap()

// Get as a slice of JsonArray
var nestedArray map[string]JsonArray = object.AsArrayMap()

// Get as a slice of JsonObject
var objectArray map[string]JsonObject = object.AsObjectMap()

As Maps with Nullable Values

If the object contains null values, and you want to represent that as nil value instead of zero value, you can use one of the following functions that returns a pointer rather than a value which allows nil. This set of methods do not set the LastError when a null value was found but instead returns it without reporting an error.

Note! This applies only for the scalar types. JsonObject and JsonArray will return an instance anyway, and you should use the IsNull() method to check if they are null.

// Get the JsonObject as map of string and nullable strings
var nullableStringMap map[string]*string = object.AsStringMapN()

// Get the JsonObject as map of string and nullable ints
var nullableIntMap map[string]*int = object.AsIntMapN()

// Get the JsonObject as map of string and nullable floats
var nullableSloatMap map[string]*float64 = object.AsFloatMapN()

Arrays

// Get array from object
features := object.GetArray("features")

// Get features length
arrayLen := features.Length() // 2

// Get an element of features by index
secondElement := features.Get(1)

// Iterating over an array
for _, feature := range features.Elements() {
    fmt.Println(feature.AsString) // tall, ...
}

As Arrays

You can also get the array as a slice of scalars (string, int, etc.). Values that are JSON null will be returned as Go zero value. If you want to regard null values, call the function with the suffix N (see next section). If a null was found, LastError will be set and report a null conversion error. For more information, see error handling.

// Get the JsonArray as a slice of string
var stringArray []string = array.AsStringArray()

// Get the JsonArray as a slice of int
var intArray []int = array.AsIntArray()

// Get the JsonArray as a slice of float
var floatArray []float64 = array.AsFloatArray()

// Get the JsonArray as a slice of JsonArray
var nestedArray []JsonArray = array.As2DArray()

// Get the JsonArray as a slice of JsonObject
var objectArray []JsonObject = array.AsObjectArray()

As Arrays of Nullable Values

If the array contains null values, and you want to represent that as nil value instead of zero value, you can use one of the following functions that returns a pointer rather than a value which allows nil. This set of methods do not set the LastError when a null value was found but instead returns it without reporting an error.

Note! This applies only for the scalar types. JsonObject and JsonArray will return an instance anyway, and you should use the IsNull() method to check if they are null.

// Get the JsonArray as a slice of nullable strings
var nullableStringArray []*string = array.AsStringArrayN()

// Get the JsonArray as a slice of nullable ints
var nullableIntArray []*int = array.AsIntArrayN()

// Get the JsonArray as a slice of nullable floats
var nullableSloatArray []*float64 = array.AsFloatArrayN()

Time

To get a string value as time.Time

var birthday time.Time = object.GetTime("birthday") // 1981-10-08T00:00:00Z
var birthday time.Time = array.GetTime(0)
var birthday time.Time = mapper.AsTime()

The mapper will try to format the string against different time formats to increase the chance of correct parsing. The following formats are supported:

time.RFC3339 time.RFC850 time.RFC822 time.RFC822Z time.RFC1123 time.RFC1123Z time.RFC3339Nano time.ANSIC time.UnixDate time.RubyDate time.Layout time.Kitchen time.Stamp time.StampMilli time.StampMicro time.StampNano time.DateTime time.DateOnly time.TimeOnly

UUID

You can also get a string value as uuid.UUID type

var uuidValue uuid.UUID = object.GetUUID("id")
var uuidValue uuid.UUID = array.GetUUID(0)
var uuidValue uuid.UUID = mapper.AsUUID()

Types

To check what type is your JsonMapper currently holding, use

fmt.Println(mapper.IsObject)    // true
fmt.Println(mapper.IsBool)      // false
fmt.Println(mapper.IsInt)       // false
fmt.Println(mapper.IsFloat)     // false
fmt.Println(mapper.IsString)    // false
fmt.Println(mapper.IsArray)     // false
fmt.Println(mapper.IsNull)      // false

Get JSON String

Every JSON element - JsonObject, JsonArray or JsonMapper - have the method String() and PrettyString(). The returned string from these methods will be a valid JSON. For example

fmt.Println(mapper.AsObject.String())
// output: {"age":43,"children":{"Rachel":{"age":15,"is_funny":false},"Sara":{"age":19,"is_funny":true}},"features":["tall","blue eyes"],"is_funny":false,"name":"Jason"}

fmt.Println(mapper.AsObject.Get("children").String())
// output: {"Rachel":{"age":15,"is_funny":false},"Sara":{"age":19,"is_funny":true}}

or with PrettyString()

fmt.Println(object.GetObject("children").PrettyString())
// output:
// {
//   "address": null,
//   "age": 43,
//   "birthday": "1981-10-08",
//   "children": {
//     "Rachel": {
//       "age": 15,
//       "is_funny": false
//     },
//     "Sara": {
//       "age": 19,
//       "is_funny": true
//     }
//   },
//   "features": [
//     "tall",
//     "blue eyes",
//     null
//   ],
//   "height": 1.87,
//   "is_funny": false,
//   "name": "Jason"
// }

Write to JSON

To write a JSON object or array is as simple as reading from it.

Write Object

// Create a new object
obj := jogson.NewObject()
obj.AddKeyValue("name", "Chris")
fmt.Println(obj.String()) // {"name":"Chris"}

Write Array

// Create a new array
arr := jogson.NewArray()
arr.AddElement(15)
arr.AddElement(19)
fmt.Println(arr.String()) // [15,19]

Error Handling

Error handling is designed in such a way to not break the flow and to allow a cleaner code. In most cases errors are not returned, but instead, they are stored in an exported field, LastError, which can be found in both JsonObject and JsonArray and can be used to check for the type of error after an operation is made.

_ = object.GetString("non-existent-key")
if object.LastError != nil {
    fmt.Println(object.LastError) // output: key was not found: 'non-existent-key'
}

Note, LastError is reset at the beginning of every operation, so if you need a reference to an old error, you will have to store it in a variable. For example:

_ = object.GetString("address")
fmt.Println(object.LastError) // output: type conversion error: <nil> could not be converted to string
_ = object.GetString("name")
fmt.Println(object.LastError) // output: <nil>

Design

There are 3 structs that are important to know when working with the library

  • JsonMapper struct for generic JSON.
  • JsonObject represents JSON object.
  • JsonArray represents JSON array.

JsonMapper

JsonMapper is a struct that holds JSON data and serves as a generic type for all possible JSON types. It has AsX and IsX fields with which you can get the data and check the type, respectively. For example, if your data is a JSON object, you can call JsonMapper.AsObject, or if it's a string, JsonMapper.AsString. This struct is best used when you don't know the type at compile time and want to check it dynamically. In this case you can use JsonMapper.IsArray, JsonMapper.IsString, JsonMapper.IsFloat, etc.

Note, in any case, AsX never returns nil, but always the zero value. If the underlying data is null, then IsNull will be set to true.

JsonMapper is also returned in cases where the return type can be any JSON type. For example, JsonArray.Elements() returns a slice []JsonMapper over which you can iterate or query specific elements. Other methods that return JsonMapper (instead of JsonObject or JsonArray) are JsonObject.Values(), JsonObject.Get(), JsonArray.Get(), JsonArray.Find() and more.

JsonObject

JsonObject holds JSON object data and has different methods to read from JSON object and write to it. Once you have an instance, you can use the various methods to read or write data to you object. There are multiple ways to get a JsonObject. You can parse it directly, get it as an element of an array, or a value in a parent object.

There are 3 sets of methods that you can use when working with JsonObject.

  • GetX(key string): gets a value in the object as the requested type. For example, GetString("key") gets the value associated with key as type string
  • AsXMap(): gets the value as the requested type. For example, AsStringMap("key") gets the value associated with key as type map[string]string
  • AddX(key string, value X): adds value, associated with key, to the object as the requested type. For example, AddString("key", "string_value") adds the string string_value associated with the key

JsonArray

JsonArray is in many ways almost identical to JsonObject. It also contains the underlying array and methods to read and write data, and both also keep the same names for the methods. However, they have some minor differences. You can read more about them in the next section.

JsonObject and JsonArray Similarities and Differences

The structs JsonObject and JsonArray have very similar methods, both in naming and semantics. For example, both structs have GetString(), GetInt(), GetFloat(), IsNull(), IsEmpty() and other methods that are identical in names. Additionally, they both have similar method names with the similar semantics. For example, JsonObject.AsStringMap will return map[string]string, whereas JsonArray.AsStringArray will return []string.

As a rule of thumb, they have 2 differences:

  • Input:
    • JsonObject's methods mostly take a string as the key, e.g. GetInt("age").
    • JsonArray's methods mostly take an int as the index, e.g. GetBool(1).
  • Output:
    • JsonObject's methods mostly return a map or JsonObject, e.g. GetFloatMap() -> map[string]string.
    • JsonArray's methods mostly return a slice or JsonArray, e.g. GetFloatArray(1) -> []float.

Methods and Variables Prefix

The prefixes, As, Is, Get and Add have similar semantics across the library and can be found in JsonMapper, JsonObject and JsonArray.

  • IsX: checks for the value's type. For example JsonMapper.IsBool
  • AsX: converts the current data to other type representation. For example, JsonArray.AsStringArray() converts JsonArray to []string.
  • GetX: Fetches the data, usually with some sort of search in the underlying data.
  • AddX: Adds the data to the JSON array or object