There are 2 methods we should first describe to understand how persisting works in MikroORM:
em.persist() and em.flush().
em.persist(entity, flush?: boolean) is used to mark new entities for future persisting.
It will make the entity managed by given EntityManager and once flush will be called, it
will be written to the database. Second boolean parameter can be used to invoke flush
immediately. Its default value is configurable via autoFlush option.
To understand flush, lets first define what managed entity is: An entity is managed if
it’s fetched from the database (via em.find(), em.findOne() or via other managed entity)
or registered as new through em.persist().
em.flush() will go through all managed entities, compute appropriate change sets and
perform according database queries. As an entity loaded from database becomes managed
automatically, you do not have to call persist on those, and flush is enough to update
them.
const book = await orm.em.findOne(Book, 1);
book.title = 'How to persist things...';
// no need to persist `book` as its already managed by the EM
await orm.em.flush();To save entity state to database, you need to persist it. Persist takes care or deciding
whether to use insert or update and computes appropriate change-set. Entity references
that are not persisted yet (does not have identifier) will be cascade persisted automatically.
// use constructors in your entities for required parameters
const author = new Author('Jon Snow', 'snow@wall.st');
author.born = new Date();
const publisher = new Publisher('7K publisher');
const book1 = new Book('My Life on The Wall, part 1', author);
book1.publisher = publisher;
const book2 = new Book('My Life on The Wall, part 2', author);
book2.publisher = publisher;
const book3 = new Book('My Life on The Wall, part 3', author);
book3.publisher = publisher;
// just persist books, author and publisher will be automatically cascade persisted
await orm.em.persistAndFlush([book1, book2, book3]);
// or one by one
orm.em.persistLater(book1);
orm.em.persistLater(book2);
orm.em.persistLater(book3);
await orm.em.flush(); // flush everything to database at onceSince MikroORM v3, default value for autoFlush is false. That means you need to call
em.flush() yourself to persist changes into database. You can still change this via ORM's
options to ease the transition but generally it is not recommended.
orm.em.persist(new Entity()); // no auto-flushing by default
await orm.em.flush();
await orm.em.persist(new Entity(), true); // you can still use second parameter to auto-flushTo fetch entities from database you can use find() and findOne() of EntityManager:
Example:
const author = await orm.em.findOne(Author, '...id...');
const books = await orm.em.find(Book, {});
for (const author of authors) {
console.log(author.name); // Jon Snow
for (const book of author.books) {
console.log(book.title); // initialized
console.log(book.author.isInitialized()); // true
console.log(book.author.id);
console.log(book.author.name); // Jon Snow
console.log(book.publisher); // just reference
console.log(book.publisher.isInitialized()); // false
console.log(book.publisher.id);
console.log(book.publisher.name); // undefined
}
}Querying entities via conditions object (where in em.find(Entity, where: FilterQuery<T>))
supports many different ways:
// search by entity properties
const users = await orm.em.find(User, { firstName: 'John' });
// for searching by reference you can use primary key directly
const id = 1;
const users = await orm.em.find(User, { organization: id });
// or pass unpopulated reference (including `Reference` wrapper)
const ref = await orm.em.getReference(Organization, id);
const users = await orm.em.find(User, { organization: ref });
// fully populated entities as also supported
const ent = await orm.em.findOne(Organization, id);
const users = await orm.em.find(User, { organization: ent });
// complex queries with operators
const users = await orm.em.find(User, { $and: [{ id: { $nin: [3, 4] } }, { id: { $gt: 2 } }] });
// you can also search for array of primary keys directly
const users = await orm.em.find(User, [1, 2, 3, 4, 5]);
// and in findOne all of this works, plus you can search by single primary key
const user1 = await orm.em.findOne(User, 1);As you can see in the fifth example, one can also use operators like $and, $or, $gte,
$gt, $lte, $lt, $in, $nin, $eq, $ne. More about that can be found in
Query Conditions section.
When fetching single entity, you can choose to select only parts of an entity via options.fields:
const author = await orm.em.findOne(Author, '...', { fields: ['name', 'born'] });
console.log(author.id); // PK is always selected
console.log(author.name); // Jon Snow
console.log(author.email); // undefinedIf you are going to paginate your results, you can use em.findAndCount() that will return
total count of entities before applying limit and offset.
const [authors, count] = await orm.em.findAndCount(Author, { ... }, { limit: 10, offset: 50 });
console.log(authors.length); // based on limit parameter, e.g. 10
console.log(count); // total count, e.g. 1327When you call em.findOne() and no entity is found based on your criteria, null will be
returned. If you rather have an Error instance thrown, you can use em.findOneOrFail():
const author = await orm.em.findOne(Author, { name: 'does-not-exist' });
console.log(author === null); // true
try {
const author = await orm.em.findOneOrFail(Author, { name: 'does-not-exist' });
// author will be always found here
} catch (e) {
console.error('Not found', e);
}You can customize the error either globally via findOneOrFailHandler option, or locally via
failHandler option in findOneOrFail call.
try {
const author = await orm.em.findOneOrFail(Author, { name: 'does-not-exist' }, {
failHandler: (entityName: string, where: Record<string, any> | IPrimaryKey) => new Error(`Failed: ${entityName} in ${util.inspect(where)}`)
});
} catch (e) {
console.error(e); // your custom error
}Both EntityManager.find and EntityManager.findOne() methods have generic return types.
All of following examples are equal and will let typescript correctly infer the entity type:
const author1 = await orm.em.findOne<Author>(Author.name, '...id...');
const author2 = await orm.em.findOne<Author>('Author', '...id...');
const author3 = await orm.em.findOne(Author, '...id...');As the last one is the least verbose, it should be preferred.
Although you can use EntityManager directly, much more convenient way is to use
EntityRepository instead. You can register
your repositories in dependency injection container like InversifyJS
so you do not need to get them from EntityManager each time.
For more examples, take a look at
tests/EntityManager.mongo.test.ts
or tests/EntityManager.mysql.test.ts.
Returns EntityRepository for given entity, respects customRepository option of @Entity
and entityRepository option of MikroORM.init().
find<T extends IEntity>(entityName: string | EntityClass<T>, where: FilterQuery<T>, options?: FindOptions): Promise<T[]>
Returns array of entities found for given condition. You can specify FindOptions to request
population of referenced entities or control the pagination:
export interface FindOptions {
populate?: string[];
orderBy?: { [k: string]: QueryOrder };
limit?: number;
offset?: number;
}find<T extends IEntity>(entityName: string | EntityClass<T>, where: FilterQuery<T>, populate?: string[], orderBy?: { [k: string]: QueryOrder }, limit?: number, offset?: number): Promise<T[]>
Same as previous find method, just with dedicated parameters for populate, orderBy, limit
and offset.
findAndCount<T extends IEntity>(entityName: string | EntityClass<T>, where: FilterQuery<T>, populate?: string[], orderBy?: { [k: string]: QueryOrder }, limit?: number, offset?: number): Promise<[T[], number]>
Combination of find and count methods.
findOne<T extends IEntity>(entityName: string | EntityClass<T>, where: FilterQuery<T> | IPrimaryKey, populate?: string[]): Promise<T | null>
Finds an entity by given where condition. You can use primary key as where value, then
if the entity is already managed, no database call will be made.
findOneOrFail<T extends IEntity>(entityName: string | EntityClass<T>, where: FilterQuery<T> | IPrimaryKey, populate?: string[]): Promise<T>
Just like findOne, but throws when entity not found, so it always resolves to given entity.
You can customize the error either globally via findOneOrFailHandler option, or locally via
failHandler option in findOneOrFail call.
Adds given entity to current Identity Map. After merging, entity becomes managed. This is useful when you want to work with cached entities.
Maps raw DB result to entity, adding it to current Identity Map. Equivalent to
IDatabaseDriver.mapResult() followed by EntityManager.merge().
Gets a reference to the entity identified by the given type and identifier without actually loading it, if the entity is not yet loaded.
Gets count of entities matching the where condition.
Tells the EntityManager to make an instance managed and persistent. The entity will be
entered into the database at or before transaction commit or as a result of the flush
operation. You can control immediate flushing via flush parameter and via autoFlush
configuration option.
Shortcut for persist & flush.
Shortcut for just persist, without flushing.
Flushes all changes to objects that have been queued up to now to the database.
remove(entityName: string | EntityClass<T>, where: IEntity | FilterQuery<T> | IPrimaryKey, flush?: boolean): Promise<number>
When provided entity instance as where value, then it calls removeEntity(entity, flush),
otherwise it fires delete query with given where condition.
This method fires beforeDelete and afterDelete hooks only if you provide entity instance.
Removes an entity instance. A removed entity will be removed from the database at or before
transaction commit or as a result of the flush operation. You can control immediate flushing
via flush parameter and via autoFlush configuration option.
This method fires beforeDelete and afterDelete hooks.
Shortcut for removeEntity & flush.
Shortcut for removeEntity without flushing.
Clears the EntityManager. All entities that are currently managed by this EntityManager become detached.
Returns whether given entity has given property which can be populated (is reference or collection).