GoLang GORM Cyclical Binary Tree - go

Question

I'm trying to model a database in GoLang (go 1.16) using GORM (gorm.io/gorm v1.21.9).
Part of my schema includes table A with 2 optional foreign keys, in practice only 1 will be used for each record. Table B contains 2 references to table A, like a binary tree. Table C is a leaf node.
Figure 1. Entity Relationship Diagram
Figure 2. Example Usage
I have the GORM code set up as shown below.
type A struct {
ID string
BID *string
B *B
CID *string
C *C
}
type B struct {
ID string
LeftAID string
LeftA A
RightAID string
RightA A
}
type C struct {
ID string
}
When I load the application with sample data, table B always has null values for it's foreign keys.
However, Table A has a value for table_b_id for every record (should be null when table_c_id exists).
I'm guessing that, since table A has a foreign key to table B, it's using that association in all cases, instead of picking up the right_a_id and left_a_id associations. Is there a GORM annotation that will fix this, or is this a limitation inherent to GORM?
Please note that I have removed the unrelated schema information and used abstracted table/column names.

Answer 1

Maybe you should uses
Self-Referential Has One
Self-Referential Has One
like follow
type A struct {
ID string
LeftID *string
LeftA *A `gorm:"foreignkey:LeftID"`
RightID *string
RightA *A `gorm:"foreignkey:RightID"`
LeafID *string
LeafA *A `gorm:"foreignkey:LeafID"`
}
test code:
func main() {
db := config.CreateMysql()
db.AutoMigrate(&A{})
a1 := A{ID: "a1"}
a2 := A{ID: "a2"}
a3 := A{ID: "a3"}
a4 := A{ID: "a4"}
a5 := A{ID: "a5"}
a1.LeftA = &a2
a1.RightA = &a3
a4.LeafA = &a5
db.Create(&a1)
db.Create(&a4)
}
in db like this: