Mixin

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.
    }
}