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Mixin

A Mixin allows you to create reusable pieces of ent.Schema code that can be injected into other schemas using composition.

The ent.Mixin interface is as follows:

type Mixin interface {
// Fields returns a slice of fields to add to the schema.
Fields() []Field
// Edges returns a slice of edges to add to the schema.
Edges() []Edge
// Indexes returns a slice of indexes to add to the schema.
Indexes() []Index
// Hooks returns a slice of hooks to add to the schema.
// Note that mixin hooks are executed before schema hooks.
Hooks() []Hook
// Policy returns a privacy policy to add to the schema.
// Note that mixin policy are executed before schema policy.
Policy() Policy
// Annotations returns a list of schema annotations to add
// to the schema annotations.
Annotations() []schema.Annotation
}

Example#

A common use case for Mixin is to mix-in a list of common fields to your schema.

package schema
import (
"time"
"entgo.io/ent"
"entgo.io/ent/schema/field"
"entgo.io/ent/schema/mixin"
)
// -------------------------------------------------
// Mixin definition
// TimeMixin implements the ent.Mixin for sharing
// time fields with package schemas.
type TimeMixin struct{
// We embed the `mixin.Schema` to avoid
// implementing the rest of the methods.
mixin.Schema
}
func (TimeMixin) Fields() []ent.Field {
return []ent.Field{
field.Time("created_at").
Immutable().
Default(time.Now),
field.Time("updated_at").
Default(time.Now).
UpdateDefault(time.Now),
}
}
// DetailsMixin implements the ent.Mixin for sharing
// entity details fields with package schemas.
type DetailsMixin struct{
// We embed the `mixin.Schema` to avoid
// implementing the rest of the methods.
mixin.Schema
}
func (DetailsMixin) Fields() []ent.Field {
return []ent.Field{
field.Int("age").
Positive(),
field.String("name").
NotEmpty(),
}
}
// -------------------------------------------------
// Schema definition
// User schema mixed-in the TimeMixin and DetailsMixin fields and therefore
// has 5 fields: `created_at`, `updated_at`, `age`, `name` and `nickname`.
type User struct {
ent.Schema
}
func (User) Mixin() []ent.Mixin {
return []ent.Mixin{
TimeMixin{},
DetailsMixin{},
}
}
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("nickname").
Unique(),
}
}
// Pet schema mixed-in the DetailsMixin fields and therefore
// has 3 fields: `age`, `name` and `weight`.
type Pet struct {
ent.Schema
}
func (Pet) Mixin() []ent.Mixin {
return []ent.Mixin{
DetailsMixin{},
}
}
func (Pet) Fields() []ent.Field {
return []ent.Field{
field.Float("weight"),
}
}

Builtin Mixin#

Package mixin provides a few builtin mixins that can be used for adding the create_time and update_time fields to the schema.

In order to use them, add the mixin.Time mixin to your schema as follows:

package schema
import (
"entgo.io/ent"
"entgo.io/ent/schema/mixin"
)
type Pet struct {
ent.Schema
}
func (Pet) Mixin() []ent.Mixin {
return []ent.Mixin{
mixin.Time{},
// Or, mixin.CreateTime only for create_time
// and mixin.UpdateTime only for update_time.
}
}