Entity Listeners and Subscribers

​What is an Entity Listener​
​@AfterLoad​
​@BeforeInsert​
​@AfterInsert​
​@BeforeUpdate​
​@AfterUpdate​
​@BeforeRemove​
​@AfterRemove​
​What is a Subscriber​
​Event Object​
What is an Entity Listener
Any of your entities can have methods with custom logic that listen to specific entity events. You must mark those methods with special decorators depending on what event you want to listen to.
Note: Do not make any database calls within a listener, opt for subscribers instead.
@AfterLoad
You can define a method with any name in entity and mark it with @AfterLoad and TypeORM will call it each time the entity is loaded using QueryBuilder or repository/manager find methods. Example:
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@Entity()
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export class Post {
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​
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    @AfterLoad()
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    updateCounters() {
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        if (this.likesCount === undefined)
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            this.likesCount = 0;
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    }
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}
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@BeforeInsert
You can define a method with any name in entity and mark it with @BeforeInsert and TypeORM will call it before the entity is inserted using repository/manager save. Example:
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@Entity()
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export class Post {
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​
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    @BeforeInsert()
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    updateDates() {
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        this.createdDate = new Date();
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    }
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}
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@AfterInsert
You can define a method with any name in entity and mark it with @AfterInsert and TypeORM will call it after the entity is inserted using repository/manager save. Example:
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@Entity()
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export class Post {
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​
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    @AfterInsert()
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    resetCounters() {
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        this.counters = 0;
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    }
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}
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@BeforeUpdate
You can define a method with any name in the entity and mark it with @BeforeUpdate and TypeORM will call it before an existing entity is updated using repository/manager save. Keep in mind, however, that this will occur only when information is changed in the model. If you run save without modifying anything from the model, @BeforeUpdate and @AfterUpdate will not run. Example:
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@Entity()
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export class Post {
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​
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    @BeforeUpdate()
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    updateDates() {
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        this.updatedDate = new Date();
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    }
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}
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@AfterUpdate
You can define a method with any name in the entity and mark it with @AfterUpdate and TypeORM will call it after an existing entity is updated using repository/manager save. Example:
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@Entity()
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export class Post {
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​
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    @AfterUpdate()
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    updateCounters() {
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        this.counter = 0;
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    }
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}
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@BeforeRemove
You can define a method with any name in the entity and mark it with @BeforeRemove and TypeORM will call it before a entity is removed using repository/manager remove. Example:
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@Entity()
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export class Post {
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​
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    @BeforeRemove()
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    updateStatus() {
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        this.status = "removed";
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    }
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}
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@AfterRemove
You can define a method with any name in the entity and mark it with @AfterRemove and TypeORM will call it after the entity is removed using repository/manager remove. Example:
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@Entity()
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export class Post {
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​
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    @AfterRemove()
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    updateStatus() {
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        this.status = "removed";
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    }
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}
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What is a Subscriber
Marks a class as an event subscriber which can listen to specific entity events or any entity events. Events are firing using QueryBuilder and repository/manager methods. Example:
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@EventSubscriber()
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export class PostSubscriber implements EntitySubscriberInterface<Post> {
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​
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​
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    /**
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     * Indicates that this subscriber only listen to Post events.
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     */
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    listenTo() {
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        return Post;
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    }
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​
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    /**
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     * Called before post insertion.
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     */
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    beforeInsert(event: InsertEvent<Post>) {
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        console.log(`BEFORE POST INSERTED: `, event.entity);
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    }
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​
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}
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You can implement any method from EntitySubscriberInterface. To listen to any entity you just omit listenTo method and use any:
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@EventSubscriber()
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export class PostSubscriber implements EntitySubscriberInterface {
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​
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    /**
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     * Called after entity is loaded.
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     */
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    afterLoad(entity: any) {
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        console.log(`AFTER ENTITY LOADED: `, entity);
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    }
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​
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    /**
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     * Called before post insertion.
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     */
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    beforeInsert(event: InsertEvent<any>) {
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        console.log(`BEFORE POST INSERTED: `, event.entity);
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    }
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​
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    /**
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     * Called after entity insertion.
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     */
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    afterInsert(event: InsertEvent<any>) {
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        console.log(`AFTER ENTITY INSERTED: `, event.entity);
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    }
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​
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    /**
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     * Called before entity update.
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     */
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    beforeUpdate(event: UpdateEvent<any>) {
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        console.log(`BEFORE ENTITY UPDATED: `, event.entity);
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    }
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​
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    /**
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     * Called after entity update.
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     */
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    afterUpdate(event: UpdateEvent<any>) {
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        console.log(`AFTER ENTITY UPDATED: `, event.entity);
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    }
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​
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    /**
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     * Called before entity removal.
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     */
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    beforeRemove(event: RemoveEvent<any>) {
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        console.log(`BEFORE ENTITY WITH ID ${event.entityId} REMOVED: `, event.entity);
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    }
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​
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    /**
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     * Called after entity removal.
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     */
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    afterRemove(event: RemoveEvent<any>) {
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        console.log(`AFTER ENTITY WITH ID ${event.entityId} REMOVED: `, event.entity);
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    }
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​
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    /**
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     * Called before transaction start.
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     */
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    beforeTransactionStart(event: TransactionStartEvent) {
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        console.log(`BEFORE TRANSACTION STARTED: `, event);
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    }
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​
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    /**
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     * Called after transaction start.
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     */
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    afterTransactionStart(event: TransactionStartEvent) {
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        console.log(`AFTER TRANSACTION STARTED: `, event);
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    }
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​
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    /**
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     * Called before transaction commit.
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     */
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    beforeTransactionCommit(event: TransactionCommitEvent) {
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        console.log(`BEFORE TRANSACTION COMMITTED: `, event);
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    }
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​
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    /**
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     * Called after transaction commit.
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     */
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    afterTransactionCommit(event: TransactionCommitEvent) {
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        console.log(`AFTER TRANSACTION COMMITTED: `, event);
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    }
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​
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    /**
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     * Called before transaction rollback.
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     */
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    beforeTransactionRollback(event: TransactionRollbackEvent) {
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        console.log(`BEFORE TRANSACTION ROLLBACK: `, event);
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    }
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​
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    /**
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     * Called after transaction rollback.
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     */
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    afterTransactionRollback(event: TransactionRollbackEvent) {
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        console.log(`AFTER TRANSACTION ROLLBACK: `, event);
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    }
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​
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}
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Make sure your subscribers property is set in your Connection Options so TypeORM loads your subscriber.
Event Object
Excluding listenTo, all EntitySubscriberInterface methods are passed an event object that has the following base properties:
connection: Connection - Connection used in the event.
queryRunner: QueryRunner - QueryRunner used in the event transaction.
manager: EntityManager - EntityManager used in the event transaction.
See each Event's interface for additional properties.
Note: All database operations in the subscribed event listeners should be performed using the event object's queryRunner or manager instance.