具有一对多关系的实体与其自身的关联

Question

I use GORM to build model associations in Golang and I have a struct named Category. A category can have many children categories and it may have a parent category:

type Category struct {
 Name string `json:"name"`
 Parent Category `json:"parent_category"`
 ParentGroupID uint `json:"parent_group_id"`
 Children []Category `json:"children_categories"`
}

For this struct, I got an error for Invalid recursive type Category. I checked the GORM documentation but did not find anything helpful there. Any ideas how to model this kind of relation with GORM?

Answer 1

You must declare Parent as *Category (a pointer to Category) instead of Category.

type Category struct {
 Name string `json:"name"`
 Parent *Category `json:"parent_category"`
 ParentGroupID uint `json:"parent_group_id"`
 Children []Category `json:"children_categories"`
}

How does compiler know what the size of Parent is. A pointer's size is known, but how big is something that contains itself? (And the inner struct contains itself as well, as does the inner inner struct, and so on.)

Reference: https://stackoverflow.com/a/8261789/4794989