Has One
A has one
association sets up a one-to-one connection with another model, but with somewhat different semantics (and consequences). This association indicates that each instance of a model contains or possesses one instance of another model.
For example, if your application includes users and credit cards, and each user can only have one credit card.
Declare
// User has one CreditCard, UserID is the foreign key |
Retrieve
// Retrieve user list with eager loading credit card |
Override Foreign Key
For a has one
relationship, a foreign key field must also exist, the owner will save the primary key of the model belongs to it into this field.
The field’s name is usually generated with has one
model’s type plus its primary key
, for the above example it is UserID
.
When you give a credit card to the user, it will save the User’s ID
into its UserID
field.
If you want to use another field to save the relationship, you can change it with tag foreignKey
, e.g:
type User struct { |
Override References
By default, the owned entity will save the has one
model’s primary key into a foreign key, you could change to save another field’s value, like using Name
for the below example.
You are able to change it with tag references
, e.g:
type User struct { |
CRUD with Has One
Please checkout Association Mode for working with has one
relations
Eager Loading
GORM allows eager loading has one
associations with Preload
or Joins
, refer Preloading (Eager loading) for details
Self-Referential Has One
type User struct { |
FOREIGN KEY Constraints
You can setup OnUpdate
, OnDelete
constraints with tag constraint
, it will be created when migrating with GORM, for example:
type User struct { |
You are also allowed to delete selected has one associations with Select
when deleting, checkout Delete with Select for details