ent/doc/md/schema-fields.md

---
id: schema-fields
title: 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](https://entgo.io/images/assets/er_fields_properties.png)

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

```go
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).

```go
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](migrate.md) 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](code-gen.md#code-generation-options))
and auto-incremented in the database.

In order to configure the `id` field to be unique across all tables, use the
[WithGlobalUniqueID](migrate.md#universal-ids) 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:

```go
// 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](faq.md#how-do-i-use-a-custom-generator-of-ids) for more information.

```go
// 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.

```go
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, or a type that implements the
[ValueScanner](https://pkg.go.dev/entgo.io/ent/schema/field?tab=doc#ValueScanner) interface.


```go
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.Unknown),
		field.Float("decimal").
			// A ValueScanner type mixed with SchemaType.
			GoType(decimal.Decimal{}).
			SchemaType(map[string]string{
			    dialect.MySQL:    "decimal(6,2)",
			    dialect.Postgres: "numeric",
			}),
	}
}
```

## 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

```go
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.

```go
// 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),
	}
}
```

SQL-specific expressions like function calls can be added to default value configuration using the
[`entsql.Annotation`](https://pkg.go.dev/entgo.io/ent@master/dialect/entsql#Annotation):

```go
// 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.Annotation{
				Default: "CURRENT_TIMESTAMP",
			}),
	}
}
```

In case your `DefaultFunc` is also returning an error, it is better to handle it properly using [schema-hooks](hooks.md#schema-hooks).
See [this FAQ](faq.md#how-to-use-a-custom-generator-of-ids) 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.

```go
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:

```go
// 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").
	Validate(MaxRuneCount(10))
field.String("nickname").
	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`

## 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.


```go
// 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 data.

For example, given this schema:
```go
// 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:

```go
// 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"`
}
```

## 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 entity updater.

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

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

## 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.

```go
// 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](schema-indexes.md) 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.

```go
// 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:

```go
// 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:

```go
// 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](code-gen.md/#external-templates). For example:

```gotemplate
{{ 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:

```go
// 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.

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

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

## 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).

```go
// 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](templates.md#annotations).

## 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.