snapshot of https://github.com/ent/ent.git (master, 2026-09-15; blobs > 131072B omitted)

doc/md/schema-mixin.md

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+---
+id: schema-mixin
+title: 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:
+
+```go
+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.
+
+```go
+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:
+```go
+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.
+	}
+}
+```