如何获取/打印一片数组指针的内容？

Question

I have the following struct and function:

type RayTrace struct {
    gorm.Model
    Var1   float64 `json:"var1"`
    Var2   float64 `json:"var2"`
    Var3   float64 `json:"var3"`
    UserID uint    `json:"user_id"`
}

...

// GetRaytracesFor function
func GetRaytracesFor(id uint) []*RayTrace {
    raytraces := make([]*RayTrace, 0)
    err := GetDB().Table("ray_traces").Where("user_id = ?", id).Last(&raytraces).Error
    if err != nil {
        return nil
    }
    return raytraces
}

How can I get/print the data returned from the db call?

Thanks!

Answer 1

I assume you're asking how to print the values of slice of pointers, not the address. In this case, using fmt.Println(raytraces) or fmt.Printf("%v", raytraces) // or %+v or %#v will return the addresses.

You might want to see similar question golang how to print struct value with pointer .

Basically, you need to print the fields manually. Here's some different ways to do it:

1. Loop through the slice and print the value by dereferencing the element

func GetRaytracesFor(id uint) []*RayTrace {
    raytraces := make([]*RayTrace, 0)
    err := GetDB().Table("ray_traces").Where("user_id = ?", id).Last(&raytraces).Error
    if err != nil {
        return nil
    }

    for _, raytrace := range raytraces {
        // before dereferencing pointer, check if nil
        if raytrace == nil {
            fmt.Println("<nil>")
            continue
        }
        // notice the * before raytrace
        fmt.Printf("%+v\n", *raytrace)
    }
    return raytraces
}

2. Make type RayTrace implements fmt.Stringer

// implements fmt.Stringer
func (r RayTrace) String() string {
    return fmt.Sprintf("RayTrace{Var1:%v Var2:%v Var3:%v UserID:%v}", r.Var1, r.Var2, r.Var3, r.UserID)
}

func GetRaytracesFor(id uint) []*RayTrace {
    raytraces := make([]*RayTrace, 0)
    err := GetDB().Table("ray_traces").Where("user_id = ?", id).Last(&raytraces).Error
    if err != nil {
        return nil
    }

    // now we can print anywhere without need to loop each element
    fmt.Println(raytraces)

    return raytraces
}

More to read:

golang how to print struct value with pointer

https://golang.org/pkg/fmt/#Printf

https://golang.org/pkg/fmt/#Stringer