title | sidebar_label |
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Working with Entity Manager |
Entity Manager |
There are 2 methods we should first describe to understand how persisting works in MikroORM:
em.persist()
and em.flush()
.
em.persist(entity)
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.
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 determines
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.persist(book1);
orm.em.persist(book2);
orm.em.persist(book3);
await orm.em.flush(); // flush everything to database at once
To 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
}
}
To populate entity relations, you can use populate
parameter.
const books = await orm.em.find(Book, { foo: 1 }, ['author.friends']);
You can also use em.populate()
helper to populate relations (or to ensure they
are fully populated) on already loaded entities. This is also handy when loading
entities via QueryBuilder
:
const authors = await orm.em.createQueryBuilder(Author).select('*').getResult();
await em.populate(authors, ['books.tags']);
// now your Author entities will have `books` collections populated,
// as well as they will have their `tags` collections populated.
console.log(authors[0].books[0].tags[0]); // initialized BookTag
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
, $like
, $re
. More about that can be found in
Query Conditions section.
Sometimes you might be facing TypeScript errors caused by too complex query for it to properly infer all types. Usually it can be solved by providing the type argument explicitly.
You can also opt in to use repository instead, as there the type inference should not be problematic.
As a last resort, you can always type cast the query to
any
.
const books = await orm.em.find<Book>(Book, { ... your complex query ... });
// or
const books = await orm.em.getRepository(Book).find({ ... your complex query ... });
// or
const books = await orm.em.find<any>(Book, { ... your complex query ... }) as Book[];
Another problem you might be facing is RangeError: Maximum call stack size exceeded
error
thrown during TypeScript compilation (usually from file node_modules/typescript/lib/typescript.js
).
The solution to this is the same, just provide the type argument explicitly.
You can also search by referenced entity properties. Simply pass nested where condition like this and all requested relationships will be automatically joined. Currently it will only join them so you can search and sort by those. To populate entities, do not forget to pass the populate parameter as well.
// find author of a book that has tag specified by name
const author = await orm.em.findOne(Author, { books: { tags: { name: 'Tag name' } } });
console.log(author.books.isInitialized()); // false, as it only works for query and sort
const author = await orm.em.findOne(Author, { books: { tags: { name: 'Tag name' } } }, ['books.tags']);
console.log(author.books.isInitialized()); // true, because it was populated
console.log(author.books[0].tags.isInitialized()); // true, because it was populated
console.log(author.books[0].tags[0].isInitialized()); // true, because it was populated
This feature is fully available only for SQL drivers. In MongoDB always you need to query from the owning side - so in the example above, first load book tag by name, then associated book, then the author. Another option is to denormalize the schema.
This feature is supported only for
SELECT_IN
loading strategy.
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); // undefined
If 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. 1327
When 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
}
It is possible to use any SQL fragment in your WHERE
query or ORDER BY
clause:
The
expr()
helper is an identity function - all it does is to return its parameter. We can use it to bypass the strict type checks inFilterQuery
.
const users = await orm.em.find(User, { [expr('lower(email)')]: 'foo@bar.baz' }, {
orderBy: { [`(point(loc_latitude, loc_longitude) <@> point(0, 0))`]: 'ASC' },
});
This will produce following query:
select `e0`.*
from `user` as `e0`
where lower(email) = 'foo@bar.baz'
order by (point(loc_latitude, loclongitude) <@> point(0, 0)) asc
Both em.find
and em.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
.