Gorm: unsupported destination, should be slice or struct

Created on 19 Jun 2017 · 3Comments · Source: go-gorm/gorm

What version of Go are you using (`go version`)?

golang 1.8.3

Which database and its version are you using?

mysql 5.6

What did you do?

Please provide a complete runnable program to reproduce your issue.

package main

import (
    "fmt"

    _ "github.com/go-sql-driver/mysql"
    "github.com/jinzhu/gorm"
)

var db *gorm.DB

func find(v *map[string]interface{}) {

}

func main() {
    var err error
    db, err = gorm.Open("mysql", "***")
    if err != nil {
        panic(err)
    }
    var user map[string]interface{}
    db.Debug().Table("test").Find(&user)
    fmt.Println(user)
}

Like this demo.I want search some rows from mysql, and I don't want use struct. Beacuse, when I want get a join result, I need to create a new big struct or to payload struct. I think map is good in this.

Any guys can help me ?Thx

Source

littletwolee

👍1

Most helpful comment

Maybe this can be of help:

package main

import (
    "fmt"
    "reflect"

    "github.com/jinzhu/gorm"
    _ "github.com/mattn/go-sqlite3"
)

type Project struct {
    gorm.Model
    Name string `gorm:"type:varchar(200)"`
}

func main() {
    db, _ := gorm.Open("sqlite3", "db.sqlite3?cache=shared&mode=rwc")
    db.AutoMigrate(&Project{})

    db.Create(&Project{Name: "A"}) // Demo record inserted

    // Now I would like to use reflection to be able to make a generic function
    t := reflect.TypeOf(Project{})
    fmt.Println(t)

    single := reflect.New(t).Interface()
    db.Debug().Table("projects").First(single)
    fmt.Printf("Single result > %+v\n", single) // Works with a single instance

    multiple := reflect.MakeSlice(reflect.SliceOf(t), 0, 10)
    db.Debug().Table("projects").Find(&multiple)       // Log show table and records are found
    fmt.Printf("1. Multiple result > %+v\n", multiple) // But, multiple is empty

    // Instead:

    // Create a pointer to a slice value and set it to the slice
    // multiple := reflect.MakeSlice(reflect.SliceOf(t), 0, 10)
    multiplepointer := reflect.New(multiple.Type())
    multiplepointer.Elem().Set(multiple)

    db.Debug().Table("projects").Find(multiplepointer.Interface())
    fmt.Printf("2. Multiple result > %+v\n", multiplepointer) // multiplepointer contains rows
}

martinskou on 11 Dec 2019

👍2 ❤1

All 3 comments

You have not initialized the user struct.
Try changing it to var user = make(map[string]interface{}).
Although I think only structs and slices are allowed.
I don't think it works with maps.

ktsakas on 26 Jun 2017

thx @ktsakas . I was tryed your suggest.But it not work. I think you are right, it is only struct or slices.

littletwolee on 26 Jun 2017

Maybe this can be of help:

package main

import (
    "fmt"
    "reflect"

    "github.com/jinzhu/gorm"
    _ "github.com/mattn/go-sqlite3"
)

type Project struct {
    gorm.Model
    Name string `gorm:"type:varchar(200)"`
}

func main() {
    db, _ := gorm.Open("sqlite3", "db.sqlite3?cache=shared&mode=rwc")
    db.AutoMigrate(&Project{})

    db.Create(&Project{Name: "A"}) // Demo record inserted

    // Now I would like to use reflection to be able to make a generic function
    t := reflect.TypeOf(Project{})
    fmt.Println(t)

    single := reflect.New(t).Interface()
    db.Debug().Table("projects").First(single)
    fmt.Printf("Single result > %+v\n", single) // Works with a single instance

    multiple := reflect.MakeSlice(reflect.SliceOf(t), 0, 10)
    db.Debug().Table("projects").Find(&multiple)       // Log show table and records are found
    fmt.Printf("1. Multiple result > %+v\n", multiple) // But, multiple is empty

    // Instead:

    // Create a pointer to a slice value and set it to the slice
    // multiple := reflect.MakeSlice(reflect.SliceOf(t), 0, 10)
    multiplepointer := reflect.New(multiple.Type())
    multiplepointer.Elem().Set(multiple)

    db.Debug().Table("projects").Find(multiplepointer.Interface())
    fmt.Printf("2. Multiple result > %+v\n", multiplepointer) // multiplepointer contains rows
}

martinskou on 11 Dec 2019

👍2 ❤1

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