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133 lines
3.1 KiB
Markdown
133 lines
3.1 KiB
Markdown
---
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id: schema-annotations
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title: Annotations
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---
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Schema annotations allow attaching metadata to schema objects like fields and edges and inject them to external templates.
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An annotation must be a Go type that is serializable to JSON raw value (e.g. struct, map or slice)
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and implement the [Annotation](https://pkg.go.dev/entgo.io/ent/schema?tab=doc#Annotation) interface.
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The builtin annotations allow configuring the different storage drivers (like SQL) and control the code generation output.
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## Custom Table Name
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A custom table name can be provided for types using the `entsql` annotation as follows:
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```go title="ent/schema/user.go"
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package schema
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import (
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"entgo.io/ent"
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"entgo.io/ent/dialect/entsql"
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"entgo.io/ent/schema"
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"entgo.io/ent/schema/field"
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)
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// User holds the schema definition for the User entity.
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type User struct {
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ent.Schema
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}
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// Annotations of the User.
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func (User) Annotations() []schema.Annotation {
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return []schema.Annotation{
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entsql.Annotation{Table: "Users"},
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}
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}
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// Fields of the User.
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func (User) Fields() []ent.Field {
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return []ent.Field{
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field.Int("age"),
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field.String("name"),
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}
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}
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```
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## Foreign Keys Configuration
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Ent allows to customize the foreign key creation and provide a [referential action](https://dev.mysql.com/doc/refman/8.0/en/create-table-foreign-keys.html#foreign-key-referential-actions)
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for the `ON DELETE` clause:
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```go title="ent/schema/user.go"
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package schema
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import (
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"entgo.io/ent"
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"entgo.io/ent/dialect/entsql"
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"entgo.io/ent/schema/edge"
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"entgo.io/ent/schema/field"
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)
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// User holds the schema definition for the User entity.
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type User struct {
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ent.Schema
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}
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// Fields of the User.
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func (User) Fields() []ent.Field {
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return []ent.Field{
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field.String("name").
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Default("Unknown"),
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}
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}
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// Edges of the User.
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func (User) Edges() []ent.Edge {
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return []ent.Edge{
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edge.To("posts", Post.Type).
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Annotations(entsql.Annotation{
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OnDelete: entsql.Cascade,
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}),
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}
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}
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```
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The example above configures the foreign key to cascade the deletion of rows in the parent table to the matching
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rows in the child table.
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## Database Comments
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By default, column comments are not stored in the database. However, this functionality can be enabled by using the
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`WithComments(true)` annotation. For example:
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```go title="ent/schema/user.go" {17-19,32-35}
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package schema
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import (
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"entgo.io/ent"
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"entgo.io/ent/dialect/entsql"
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"entgo.io/ent/schema/field"
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)
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// User holds the schema definition for the User entity.
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type User struct {
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ent.Schema
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}
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// Annotations of the User.
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func (User) Annotations() []schema.Annotation {
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return []schema.Annotation{
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// Adding this annotation on the
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// type enables it for all fields.
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entsql.WithComments(true),
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}
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}
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// Fields of the User.
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func (User) Fields() []ent.Field {
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return []ent.Field{
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field.String("name").
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Comment("The user's name"),
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field.Int("age").
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Comment("The user's age"),
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field.String("skipped").
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Comment("This comment won't be stored in the database").
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// Explicitly disable comments for this field.
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Annotations(
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entsql.WithComments(false),
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),
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}
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}
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```
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