rx-collection.md

RxCollection

A collection stores documents of the same type.

Creating a Collection

To create one or more collections you need a RxDatabase object which has the .addCollections()-method. Every collection needs a collection name and a valid RxJsonSchema. Other attributes are optional.

const myCollections = await myDatabase.addCollections({
  // key = collectionName
  humans: {
    schema: mySchema,
    statics: {},                          // (optional) ORM-functions for this collection
    methods: {},                          // (optional) ORM-functions for documents
    attachments: {},                      // (optional) ORM-functions for attachments
    options: {},                          // (optional) Custom parameters that might be used in plugins
    migrationStrategies: {},              // (optional)
    autoMigrate: true,                    // (optional) [default=true]
    cacheReplacementPolicy: function(){}, // (optional) custom cache replacement policy
  },
  // you can create multiple collections at once
  animals: {
    // ...
  }
});

name

The name uniquely identifies the collection and should be used to refind the collection in the database. Two different collections in the same database can never have the same name. Collection names must match the following regex: ^[a-z][a-z0-9]*$.

schema

The schema defines how the documents of the collection are structured. RxDB uses a schema format, similar to JSON schema. Read more about the RxDB schema format here.

ORM-functions

With the parameters statics, methods and attachments, you can define ORM-functions that are applied to each of these objects that belong to this collection. See ORM/DRM.

Migration

With the parameters migrationStrategies and autoMigrate you can specify how migration between different schema-versions should be done. See Migration.

Get a collection from the database

To get an existing collection from the database, call the collection name directly on the database:

// newly created collection
const collections = await db.addCollections({
  heroes: {
    schema: mySchema
  }
});
const collection2 = db.heroes;
console.log(collections.heroes === collection2); //> true

Functions

Observe $

Calling this will return an rxjs-Observable which streams every change to data of this collection.

myCollection.$.subscribe(changeEvent => console.dir(changeEvent));

// you can also observe single event-types with insert$ update$ remove$
myCollection.insert$.subscribe(changeEvent => console.dir(changeEvent));
myCollection.update$.subscribe(changeEvent => console.dir(changeEvent));
myCollection.remove$.subscribe(changeEvent => console.dir(changeEvent));

insert()

Use this to insert new documents into the database. The collection will validate the schema and automatically encrypt any encrypted fields. Returns the new RxDocument.

const doc = await myCollection.insert({
  name: 'foo',
  lastname: 'bar'
});

bulkInsert()

When you have to insert many documents at once, use bulk insert. This is much faster than calling .insert() multiple times. Returns an object with a success- and error-array.

const result = await myCollection.bulkInsert([{
  name: 'foo1',
  lastname: 'bar1'
},
{
  name: 'foo2',
  lastname: 'bar2'
}]);

// > {
//   success: [RxDocument, RxDocument],
//   error: []
// }

NOTICE: bulkInsert will not fail on update conflicts and you cannot expect that on failure the other documents are not inserted.

bulkRemove()

When you want to remove many documents at once, use bulk remove. Returns an object with a success- and error-array.

const result = await myCollection.bulkRemove([
  'primary1',
  'primary2'
]);

// > {
//   success: [RxDocument, RxDocument],
//   error: []
// }

upsert()

Inserts the document if it does not exist within the collection, otherwise it will overwrite it. Returns the new or overwritten RxDocument.

const doc = await myCollection.upsert({
  name: 'foo',
  lastname: 'bar2'
});

bulkUpsert()

Same as upsert() but runs over multiple documents. Improves performance compared to running many upsert() calls.

const docs = await myCollection.bulkUpsert([
  {
    name: 'foo',
    lastname: 'bar2'
  },
  {
    name: 'bar',
    lastname: 'foo2'
  }
]);
// > [RxDocument, RxDocument]

atomicUpsert()

When you run many upsert operations on the same RxDocument in a very short timespan, you might get a 409 Conflict error. This means that you tried to run a .upsert() on the document, while the previous upsert operation was still running. To prevent these types of errors, you can run atomic upsert operations. The behavior is similar to RxDocument.atomicUpdate.

const docData = {
    name: 'Bob', // primary
    lastName: 'Kelso'
};

myCollection.upsert(docData);
myCollection.upsert(docData);
// -> throws because of parrallel update to the same document

myCollection.atomicUpsert(docData);
myCollection.atomicUpsert(docData);
myCollection.atomicUpsert(docData);

// wait until last upsert finished
await myCollection.atomicUpsert(docData);
// -> works

find()

To find documents in your collection, use this method. See RxQuery.find().

// find all that are older than 18
const olderDocuments = await myCollection
    .find()
    .where('age')
    .gt(18)
    .exec(); // execute

findOne()

This does basically what find() does, but it returns only a single document. You can pass a primary value to find a single document more easily.

To find documents in your collection, use this method. See RxQuery.find().

// get document with name:foobar
myCollection.findOne({
  selector: {
    name: 'foo'
  }
}).exec().then(doc => console.dir(doc));

// get document by primary, functionally identical to above query
myCollection.findOne('foo')
  .exec().then(doc => console.dir(doc));

findByIds()

Find many documents by their id (primary value). This has a way better performance than running multiple findOne() or a find() with a big $or selector.

Returns a Map where the primary key of the document is mapped to the document. Documents that do not exist or are deleted, will not be inside of the returned Map.

const ids = [
  'alice',
  'bob',
  /* ... */
];
const docsMap = await myCollection.findByIds(ids);

console.dir(docsMap); // Map(2)

NOTICE: The Map returned by findByIds is not guaranteed to return elements in the same order as the list of ids passed to it.

findByIds$()

Same as findByIds() but returns an Observable that emits the Map each time a value of it has changed because of a database write.

exportJSON()

Use this function to create a json export from every document in the collection.

Before exportJSON() and importJSON() can be used, you have to add the json-dump plugin.

import { addRxPlugin } from 'rxdb';
import { RxDBJsonDumpPlugin } from 'rxdb/plugins/json-dump';
addRxPlugin(RxDBJsonDumpPlugin);

myCollection.exportJSON()
  .then(json => console.dir(json));

importJSON()

To import the json dump into your collection, use this function.

// import the dump to the database
myCollection.importJSON(json)
  .then(() => console.log('done'));

Note that importing will fire events for each inserted document.

syncCouchDB()

This method allows you to replicate data between other RxCollections, pouchdb instances or remote servers which support the couchdb-sync-protocol. Full documentation on how to use replication is here.

syncGraphQL()

This method allows you to replicate data between a RxCollection and a GraphQL endpoint. Full documentation on how to use the GraphQL replication is here.

remove()

Removes all known data of the collection and its previous versions. This removes the documents, the schemas, and older schemaVersions.

await myCollection.remove();
// collection is now removed and can be re-created

destroy()

Destroys the collection's object instance. This is to free up memory and stop all observings and replications.

await myCollection.destroy();

isRxCollection

Returns true if the given object is an instance of RxCollection. Returns false if not.

const is = isRxCollection(myObj);