Golang GORM-绕过外键的列/字段命名约定？

Is there a way to circumvent the standard naming conventions for column/field names of foreign keys? For example, the following schema works for me:

type Clown struct {
    ID              uint     `gorm:"PRIMARY_KEY;not null;AUTO_INCREMENT"`
    Name            string   `gorm:"type:varchar(50);unique_index;not null"`
    Circus          Circus   `gorm:"ForeignKey:CircusID;AssociationForeignKey:ID`
    CircusID        uint     `gorm:"not null" sql:"type:integer REFERENCES circus(id)"`
}

type Circus struct {
    ID     uint      `gorm:"PRIMARY_KEY;not null;AUTO_INCREMENT"`
    Name   string    `gorm:"type:varchar(50);unique_index;not null"`
    Clowns []Clown
}

However, if I rename the Clown's "CircusID" field/column to "Foo", it no longer works:

type Clown struct {
    ID          uint    `gorm:"PRIMARY_KEY;not null;AUTO_INCREMENT"`
    Name        string  `gorm:"type:varchar(50);unique_index;not null"`
    Circus      Circus  `gorm:"ForeignKey:Foo;AssociationForeignKey:ID`
    Foo         uint    `gorm:"not null" sql:"type:integer REFERENCES circus(id)"`
}

I get an error "invalid association []". It is important to me that I stick with the "Foo" column name since I am working with an existing database and don't want to go through the trouble of changing the name of the column. Am I missing something? Is there a way to properly specify a foreign key without calling it "{{Tablename}}ID"?