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Fields

Quick Summary​

Fields (or properties) in the schema are the attributes of the node. For example, a User with 4 fields: age, name, username and created_at:

re-fields-properties

Fields are returned from the schema using the Fields method. For example:

package schema

import (
"time"

"entgo.io/ent"
"entgo.io/ent/schema/field"
)

// User schema.
type User struct {
ent.Schema
}

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.Int("age"),
field.String("name"),
field.String("username").
Unique(),
field.Time("created_at").
Default(time.Now),
}
}

All fields are required by default, and can be set to optional using the Optional method.

Types​

The following types are currently supported by the framework:

  • All Go numeric types. Like int, uint8, float64, etc.
  • bool
  • string
  • time.Time
  • UUID
  • []byte (SQL only).
  • JSON (SQL only).
  • Enum (SQL only).
  • Other (SQL only).
package schema

import (
"time"
"net/url"

"github.com/google/uuid"
"entgo.io/ent"
"entgo.io/ent/schema/field"
)

// User schema.
type User struct {
ent.Schema
}

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.Int("age").
Positive(),
field.Float("rank").
Optional(),
field.Bool("active").
Default(false),
field.String("name").
Unique(),
field.Time("created_at").
Default(time.Now),
field.JSON("url", &url.URL{}).
Optional(),
field.JSON("strings", []string{}).
Optional(),
field.Enum("state").
Values("on", "off").
Optional(),
field.UUID("uuid", uuid.UUID{}).
Default(uuid.New),
}
}

To read more about how each type is mapped to its database-type, go to the Migration section.

ID Field​

The id field is builtin in the schema and does not need declaration. In SQL-based databases, its type defaults to int (but can be changed with a codegen option) and auto-incremented in the database.

In order to configure the id field to be unique across all tables, use the WithGlobalUniqueID option when running schema migration.

If a different configuration for the id field is needed, or the id value should be provided on entity creation by the application (e.g. UUID), override the builtin id configuration. For example:

// Fields of the Group.
func (Group) Fields() []ent.Field {
return []ent.Field{
field.Int("id").
StructTag(`json:"oid,omitempty"`),
}
}

// Fields of the Blob.
func (Blob) Fields() []ent.Field {
return []ent.Field{
field.UUID("id", uuid.UUID{}).
Default(uuid.New).
StorageKey("oid"),
}
}

// Fields of the Pet.
func (Pet) Fields() []ent.Field {
return []ent.Field{
field.String("id").
MaxLen(25).
NotEmpty().
Unique().
Immutable(),
}
}

If you need to set a custom function to generate IDs, you can use DefaultFunc to specify a function which will always be ran when the resource is created. See the related FAQ for more information.

// Fields of the User.
func (User) Fields() []ent.Field {
return []ent.Field{
field.Int64("id").
DefaultFunc(func() int64 {
// An example of a dumb ID generator - use a production-ready alternative instead.
return time.Now().Unix() << 8 | atomic.AddInt64(&counter, 1) % 256
}),
}
}

Database Type​

Each database dialect has its own mapping from Go type to database type. For example, the MySQL dialect creates float64 fields as double columns in the database. However, there is an option to override the default behavior using the SchemaType method.

package schema

import (
"entgo.io/ent"
"entgo.io/ent/dialect"
"entgo.io/ent/schema/field"
)

// Card schema.
type Card struct {
ent.Schema
}

// Fields of the Card.
func (Card) Fields() []ent.Field {
return []ent.Field{
field.Float("amount").
SchemaType(map[string]string{
dialect.MySQL: "decimal(6,2)", // Override MySQL.
dialect.Postgres: "numeric", // Override Postgres.
}),
}
}

Go Type​

The default type for fields are the basic Go types. For example, for string fields, the type is string, and for time fields, the type is time.Time. The GoType method provides an option to override the default ent type with a custom one.

The custom type must be either a type that is convertible to the Go basic type, a type that implements the ValueScanner interface, or has an External ValueScanner. Also, if the provided type implements the Validator interface and no validators have been set, the type validator will be used.

package schema

import (
"database/sql"

"entgo.io/ent"
"entgo.io/ent/dialect"
"entgo.io/ent/schema/field"
"github.com/shopspring/decimal"
)

// Amount is a custom Go type that's convertible to the basic float64 type.
type Amount float64

// Card schema.
type Card struct {
ent.Schema
}

// Fields of the Card.
func (Card) Fields() []ent.Field {
return []ent.Field{
field.Float("amount").
GoType(Amount(0)),
field.String("name").
Optional().
// A ValueScanner type.
GoType(&sql.NullString{}),
field.Enum("role").
// A convertible type to string.
GoType(role.Role("")),
field.Float("decimal").
// A ValueScanner type mixed with SchemaType.
GoType(decimal.Decimal{}).
SchemaType(map[string]string{
dialect.MySQL: "decimal(6,2)",
dialect.Postgres: "numeric",
}),
}
}

External ValueScanner​

Ent allows attaching custom ValueScanner for basic or custom Go types. This enables the use of standard schema fields while maintaining control over how they are stored in the database without implementing a ValueScanner interface. Additionally, this option enables users to use GoType that does not implement the ValueScanner, such as *url.URL.

note

At this stage, this option is only available for text and numeric fields, but it will be extended to other types in the future.

Fields with a custom Go type that implements the encoding.TextMarshaller and encoding.TextUnmarshaller interfaces can use the field.TextValueScanner as a ValueScanner. This ValueScanner calls MarshalText and UnmarshalText for writing and reading field values from the database:

field.String("big_int").
GoType(&big.Int{}).
ValueScanner(field.TextValueScanner[*big.Int]{})

Other Field​

Other represents a field that is not a good fit for any of the standard field types. Examples are a Postgres Range type or Geospatial type

package schema

import (
"entgo.io/ent"
"entgo.io/ent/dialect"
"entgo.io/ent/schema/field"

"github.com/jackc/pgtype"
)

// User schema.
type User struct {
ent.Schema
}

// Fields of the User.
func (User) Fields() []ent.Field {
return []ent.Field{
field.Other("duration", &pgtype.Tstzrange{}).
SchemaType(map[string]string{
dialect.Postgres: "tstzrange",
}),
}
}

Default Values​

Non-unique fields support default values using the Default and UpdateDefault methods. You can also specify DefaultFunc instead to have a custom generator.

// Fields of the User.
func (User) Fields() []ent.Field {
return []ent.Field{
field.Time("created_at").
Default(time.Now),
field.Time("updated_at").
Default(time.Now).
UpdateDefault(time.Now),
field.String("name").
Default("unknown"),
field.String("cuid").
DefaultFunc(cuid.New),
field.JSON("dirs", []http.Dir{}).
Default([]http.Dir{"/tmp"}),
}
}

SQL-specific literals or expressions like function calls can be added to default value configuration using the entsql.Annotation:

// Fields of the User.
func (User) Fields() []ent.Field {
return []ent.Field{
// Add a new field with CURRENT_TIMESTAMP
// as a default value to all previous rows.
field.Time("created_at").
Default(time.Now).
Annotations(
entsql.Default("CURRENT_TIMESTAMP"),
),
// Add a new field with a default value
// expression that works on all dialects.
field.String("field").
Optional().
Annotations(
entsql.DefaultExpr("lower(other_field)"),
),
// Add a new field with custom default value
// expression for each dialect.
field.String("default_exprs").
Optional().
Annotations(
entsql.DefaultExprs(map[string]string{
dialect.MySQL: "TO_BASE64('ent')",
dialect.SQLite: "hex('ent')",
dialect.Postgres: "md5('ent')",
}),
),
}
}

In case your DefaultFunc is also returning an error, it is better to handle it properly using schema-hooks. See this FAQ for more information.

Validators​

A field validator is a function from type func(T) error that is defined in the schema using the Validate method, and applied on the field value before creating or updating the entity.

The supported types of field validators are string and all numeric types.

package schema

import (
"errors"
"regexp"
"strings"
"time"

"entgo.io/ent"
"entgo.io/ent/schema/field"
)


// Group schema.
type Group struct {
ent.Schema
}

// Fields of the group.
func (Group) Fields() []ent.Field {
return []ent.Field{
field.String("name").
Match(regexp.MustCompile("[a-zA-Z_]+$")).
Validate(func(s string) error {
if strings.ToLower(s) == s {
return errors.New("group name must begin with uppercase")
}
return nil
}),
}
}

Here is another example for writing a reusable validator:

import (
"entgo.io/ent/dialect/entsql"
"entgo.io/ent/schema/field"
)

// MaxRuneCount validates the rune length of a string by using the unicode/utf8 package.
func MaxRuneCount(maxLen int) func(s string) error {
return func(s string) error {
if utf8.RuneCountInString(s) > maxLen {
return errors.New("value is more than the max length")
}
return nil
}
}

field.String("name").
// If using a SQL-database: change the underlying data type to varchar(10).
Annotations(entsql.Annotation{
Size: 10,
}).
Validate(MaxRuneCount(10))
field.String("nickname").
// If using a SQL-database: change the underlying data type to varchar(20).
Annotations(entsql.Annotation{
Size: 20,
}).
Validate(MaxRuneCount(20))

Built-in Validators​

The framework provides a few built-in validators for each type:

  • Numeric types:

    • Positive()
    • Negative()
    • NonNegative()
    • Min(i) - Validate that the given value is > i.
    • Max(i) - Validate that the given value is < i.
    • Range(i, j) - Validate that the given value is within the range [i, j].
  • string

    • MinLen(i)
    • MaxLen(i)
    • Match(regexp.Regexp)
    • NotEmpty
  • []byte

    • MaxLen(i)
    • MinLen(i)
    • NotEmpty

Optional​

Optional fields are fields that are not required in the entity creation, and will be set to nullable fields in the database. Unlike edges, fields are required by default, and setting them to optional should be done explicitly using the Optional method.

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("required_name"),
field.String("optional_name").
Optional(),
}
}

Nillable​

Sometimes you want to be able to distinguish between the zero value of fields and nil. For example, if the database column contains 0 or NULL. The Nillable option exists exactly for this.

If you have an Optional field of type T, setting it to Nillable will generate a struct field with type *T. Hence, if the database returns NULL for this field, the struct field will be nil. Otherwise, it will contain a pointer to the actual value.

For example, given this schema:

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("required_name"),
field.String("optional_name").
Optional(),
field.String("nillable_name").
Optional().
Nillable(),
}
}

The generated struct for the User entity will be as follows:

ent/user.go
package ent

// User entity.
type User struct {
RequiredName string `json:"required_name,omitempty"`
OptionalName string `json:"optional_name,omitempty"`
NillableName *string `json:"nillable_name,omitempty"`
}

Nillable required fields​

Nillable fields are also helpful for avoiding zero values in JSON marshaling for fields that have not been Selected in the query. For example, a time.Time field.

// Fields of the task.
func (Task) Fields() []ent.Field {
return []ent.Field{
field.Time("created_at").
Default(time.Now),
field.Time("nillable_created_at").
Default(time.Now).
Nillable(),
}
}

The generated struct for the Task entity will be as follows:

ent/task.go
package ent

// Task entity.
type Task struct {
// CreatedAt holds the value of the "created_at" field.
CreatedAt time.Time `json:"created_at,omitempty"`
// NillableCreatedAt holds the value of the "nillable_created_at" field.
NillableCreatedAt *time.Time `json:"nillable_created_at,omitempty"`
}

And the result of json.Marshal is:

b, _ := json.Marshal(Task{})
fmt.Printf("%s\n", b)
// {"created_at":"0001-01-01T00:00:00Z"}

now := time.Now()
b, _ = json.Marshal(Task{CreatedAt: now, NillableCreatedAt: &now})
fmt.Printf("%s\n", b)
// {"created_at":"2009-11-10T23:00:00Z","nillable_created_at":"2009-11-10T23:00:00Z"}

Immutable​

Immutable fields are fields that can be set only in the creation of the entity. i.e., no setters will be generated for the update builders of the entity.

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.Time("created_at").
Default(time.Now).
Immutable(),
}
}

Uniqueness​

Fields can be defined as unique using the Unique method. Note that unique fields cannot have default values.

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("nickname").
Unique(),
}
}

Comments​

A comment can be added to a field using the .Comment() method. This comment appears before the field in the generated entity code. Newlines are supported using the \n escape sequence.

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("name").
Default("John Doe").
Comment("Name of the user.\n If not specified, defaults to \"John Doe\"."),
}
}

Storage Key​

Custom storage name can be configured using the StorageKey method. It's mapped to a column name in SQL dialects and to property name in Gremlin.

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("name").
StorageKey("old_name"),
}
}

Indexes​

Indexes can be defined on multi fields and some types of edges as well. However, you should note, that this is currently an SQL-only feature.

Read more about this in the Indexes section.

Struct Tags​

Custom struct tags can be added to the generated entities using the StructTag method. Note that if this option was not provided, or provided and did not contain the json tag, the default json tag will be added with the field name.

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("name").
StructTag(`gqlgen:"gql_name"`),
}
}

Additional Struct Fields​

By default, ent generates the entity model with fields that are configured in the schema.Fields method. For example, given this schema configuration:

// User schema.
type User struct {
ent.Schema
}

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.Int("age").
Optional().
Nillable(),
field.String("name").
StructTag(`gqlgen:"gql_name"`),
}
}

The generated model will be as follows:

// User is the model entity for the User schema.
type User struct {
// Age holds the value of the "age" field.
Age *int `json:"age,omitempty"`
// Name holds the value of the "name" field.
Name string `json:"name,omitempty" gqlgen:"gql_name"`
}

In order to add additional fields to the generated struct that are not stored in the database, use external templates. For example:

{{ define "model/fields/additional" }}
{{- if eq $.Name "User" }}
// StaticField defined by template.
StaticField string `json:"static,omitempty"`
{{- end }}
{{ end }}

The generated model will be as follows:

// User is the model entity for the User schema.
type User struct {
// Age holds the value of the "age" field.
Age *int `json:"age,omitempty"`
// Name holds the value of the "name" field.
Name string `json:"name,omitempty" gqlgen:"gql_name"`
// StaticField defined by template.
StaticField string `json:"static,omitempty"`
}

Sensitive Fields​

String fields can be defined as sensitive using the Sensitive method. Sensitive fields won't be printed and they will be omitted when encoding.

Note that sensitive fields cannot have struct tags.

// User schema.
type User struct {
ent.Schema
}

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("password").
Sensitive(),
}
}

Enum Fields​

The Enum builder allows creating enum fields with a list of permitted values.

// Fields of the User.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("first_name"),
field.String("last_name"),
field.Enum("size").
Values("big", "small"),
}
}

When a custom GoType is being used, it is must be convertible to the basic string type or it needs to implement the ValueScanner interface.

The EnumValues interface is also required by the custom Go type to tell Ent what are the permitted values of the enum.

The following example shows how to define an Enum field with a custom Go type that is convertible to string:

// Fields of the User.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("first_name"),
field.String("last_name"),
// A convertible type to string.
field.Enum("shape").
GoType(property.Shape("")),
}
}

Implement the EnumValues interface.

package property

type Shape string

const (
Triangle Shape = "TRIANGLE"
Circle Shape = "CIRCLE"
)

// Values provides list valid values for Enum.
func (Shape) Values() (kinds []string) {
for _, s := range []Shape{Triangle, Circle} {
kinds = append(kinds, string(s))
}
return
}

The following example shows how to define an Enum field with a custom Go type that is not convertible to string, but it implements the ValueScanner interface:

// Fields of the User.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("first_name"),
field.String("last_name"),
// Add conversion to and from string
field.Enum("level").
GoType(property.Level(0)),
}
}

Implement also the ValueScanner interface.

package property

import "database/sql/driver"

type Level int

const (
Unknown Level = iota
Low
High
)

func (p Level) String() string {
switch p {
case Low:
return "LOW"
case High:
return "HIGH"
default:
return "UNKNOWN"
}
}

// Values provides list valid values for Enum.
func (Level) Values() []string {
return []string{Unknown.String(), Low.String(), High.String()}
}

// Value provides the DB a string from int.
func (p Level) Value() (driver.Value, error) {
return p.String(), nil
}

// Scan tells our code how to read the enum into our type.
func (p *Level) Scan(val any) error {
var s string
switch v := val.(type) {
case nil:
return nil
case string:
s = v
case []uint8:
s = string(v)
}
switch s {
case "LOW":
*p = Low
case "HIGH":
*p = High
default:
*p = Unknown
}
return nil
}

Combining it all together:

// Fields of the User.
func (User) Fields() []ent.Field {
return []ent.Field{
field.String("first_name"),
field.String("last_name"),
field.Enum("size").
Values("big", "small"),
// A convertible type to string.
field.Enum("shape").
GoType(property.Shape("")),
// Add conversion to and from string.
field.Enum("level").
GoType(property.Level(0)),
}
}

After code generation usage is trivial:

client.User.Create().
SetFirstName("John").
SetLastName("Dow").
SetSize(user.SizeSmall).
SetShape(property.Triangle).
SetLevel(property.Low).
SaveX(context.Background())

john := client.User.Query().FirstX(context.Background())
fmt.Println(john)
// User(id=1, first_name=John, last_name=Dow, size=small, shape=TRIANGLE, level=LOW)

Annotations​

Annotations is used to attach arbitrary metadata to the field object in code generation. Template extensions can retrieve this metadata and use it inside their templates.

Note that the metadata object must be serializable to a JSON raw value (e.g. struct, map or slice).

// User schema.
type User struct {
ent.Schema
}

// Fields of the user.
func (User) Fields() []ent.Field {
return []ent.Field{
field.Time("creation_date").
Annotations(entgql.Annotation{
OrderField: "CREATED_AT",
}),
}
}

Read more about annotations and their usage in templates in the template doc.

Naming Convention​

By convention field names should use snake_case. The corresponding struct fields generated by ent will follow the Go convention of using PascalCase. In cases where PascalCase is desired, you can do so with the StorageKey or StructTag methods.