defaults

Enabling struct with defaults values

Installation

The recommended way to install defaults

go get -u -v github.com/lycblank/defaults

Examples

Set the default value of the structure field through the structure tag

package main

import (
    "fmt"
    "github.com/lycblank/defaults"
)

func main() {
    car := &Car{}
    if err := defaults.Apply(car); err != nil {
        panic(err)
    }
    fmt.Printf("car:%+v\n", car) //Prints: car:&{Color:red Size:100 IsImport:true WheelRadius:1.01 SeatCount:4}
}

type Car struct {
    Color       string  `default:"red"`
    Size        int     `default:"100"`
    IsImport    bool    `default:"true"`
    WheelRadius float64 `default:"1.01"`
    SeatCount uint `default:"4"`
}

Set the default value of the structure through json parsing

package main

import (
    "fmt"
    "github.com/lycblank/defaults/json"
)

func main() {
    raw := `{}`
    car := &Car{}
    if err := json.Unmarshal([]byte(raw), car); err != nil {
        panic(err)
    }
    fmt.Printf("car:%+v\n", car) //Prints: car:&{Color:red Size:100 IsImport:true WheelRadius:1.01 SeatCount:4}
}

type Car struct {
    Color       string  `default:"red"`
    Size        int     `default:"100"`
    IsImport    bool    `default:"true"`
    WheelRadius float64 `default:"1.01"`
    SeatCount   uint    `default:"4"`
}

Access gin to support the default tag

package main

import (
    "fmt"
    "github.com/gin-gonic/gin/binding"
    "github.com/lycblank/defaults/validator"
)

func main() {
    validator := validator.NewStructValidatorWithDefault(binding.Validator)
    // Access gin to support the default tag
    // binding.Validator = validator.NewStructValidatorWithDefault(binding.Validator)
    carWithDefault := &CarWithDefault{}
    if err := validator.ValidateStruct(carWithDefault); err != nil {
        panic(err)
    }
    fmt.Printf("car:%+v\n", carWithDefault) //Prints: car:&{Color:red Size:100 IsImport:true WheelRadius:1.01 SeatCount:4}

    carWithoutDefault := &CarWithoutDefault{}
    if err := validator.ValidateStruct(carWithoutDefault); err != nil {
        panic(err) // panic: Key: 'CarWithoutDefault.Color' Error:Field validation for 'Color' failed on the 'required' tag
    }
}

type CarWithDefault struct {
    Color       string  `default:"red" binding:"required"`
    Size        int     `default:"100" binding:"required"`
    IsImport    bool    `default:"true" binding:"required"`
    WheelRadius float64 `default:"1.01" binding:"required"`
    SeatCount   uint    `default:"4" binding:"required"`
}

type CarWithoutDefault struct {
    Color       string  `binding:"required"`
    Size        int     `binding:"required"`
    IsImport    bool    `binding:"required"`
    WheelRadius float64 `binding:"required"`
    SeatCount   uint    `binding:"required"`
}

Set the default value of the map

package main

import (
    "fmt"
    "github.com/lycblank/defaults"
)

func main() {
    car := &Car{Wheels: map[string]*CarWheel{
        "1": {},
        "2": {},
        "3": {},
        "4": {Radius: 5},
    }}
    if err := defaults.Apply(car); err != nil {
        panic(err)
    }
    for k, v := range car.Wheels {
        fmt.Printf("%s=%+v\n", k, v)
        // Prints:
        //1=&{Color:black Radius:1.02}
        //2=&{Color:black Radius:1.02}
        //3=&{Color:black Radius:1.02}
        //4=&{Color:black Radius:5}
    }
}

type Car struct {
    Color     string               `default:"red"`
    Size      int                  `default:"100"`
    IsImport  bool                 `default:"true"`
    SeatCount uint                 `default:"4"`
    Wheels    map[string]*CarWheel // note: The value of the map needs to be a pointer type
}

type CarWheel struct {
    Color  string  `default:"black"`
    Radius float64 `default:"1.02"`
}

Caveats

A value of zero will be overwritten as the default value if the default tag is set.

License

MIT, see LICENSE