Gorm: Proper way to declare a recursive one to many or belongsTo relationship

[sredxny]

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

Go 1.10

Which database and its version are you using?

Postgres

Please provide a complete runnable program to reproduce your issue. IMPORTANT

Hello, I have been trying to make in the proper way the self-relationship, it's about a menu item that can have many sub-items, so, first: is better to track who is the parent or to know who are the children? second: I wasn't able to make it works, I tried:

type MenuItem struct{
    ID        uint `gorm:"primary_key"`
    Name string `gorm:"unique;not null"`
    Text string
    Parent *MenuItem `gorm:"association_foreignkey:Refer"`
    ParentId int `gorm:"TYPE:integer REFERENCES menuitems"`
}

But, in this case when I try to insert I get the error: (pq: insert or update on table "menuitems" violates foreign key constraint "menuitems_parent_id_fkey")
Also tried:

type MenuItem struct{
    ID        uint `gorm:"primary_key"`
    Name string `gorm:"unique;not null"`
    Text string
    Parent MenuItem `gorm:"association_foreignkey:ID"`
}

And, here I get: invalid recursive type MenuItem

Thank you and I appreciate any help!

[gstvg]

Depending on the code, may the children is being inserted first with an invalid fk to its ,at the time, un-inserted parent?

Qor Example achieves that in that way:
https://github.com/qor/qor-example/blob/ce0ab4ecdd6a2fa811e1aee4ecdeffbd8f343f08/models/products/category.go

[sredxny]

@gstvg ok, I get it. Well, when a child is inserted they could select a parent (is not strictly required), but in that case that item would be a parent (I mean, in the first level of the hierarchy). Then, I think that I have to track is who is the parent instead saving children?

[gstvg]

Depending your use case, yes, could be better to track who is the parent cause then you would have the full hierarchy on a single object, making it easier to use in templates or encoding to json,xml...

[sredxny]

@gstvg oko, in that case I implemented the relation as:

type MenuItem struct{
    ID        uint `gorm:"primary_key"`
    Name string `gorm:"unique;not null"`
    Text string
    Parent MenuItem `gorm:"association_foreignkey:ID"`
}

But, I am getting the error: invalid recursive type MenuItem
so, what am I missing?

[gstvg]

this code need to have Parent as a pointer to MenuItem:
Parent *MenuItemgorm:"association_foreignkey:ID"``

But i would write that way:

type MenuItem struct {
    ID        uint `gorm:"primary_key"`

    Name string `gorm:"unique;not null"`
    Text string
    Childs []MenuItem

        MenuItemID //parent id, would be 0 for top-level menu
}

[sredxny]

@gstvg thank you! I managed by doing:

type MenuItem struct {
    ID       uint   `gorm:"primary_key"`
    Name     string `gorm:"unique;not null"`
    Text     string
    Parent   *MenuItem `gorm:"foreignkey:ParentID"`
    ParentID uint
}

And then I was able to load the related menu-item (parent) by doing:

db.Model(&menu).Related(&menu, "ParentID")