A query allows to find documents in your collection. Like most other noSQL-Databases, RxDB uses the mango-query-syntax. It is also possible to use chained methods.


To create a basic RxQuery, call .find() on a collection and insert selectors. The result-set of normal queries is an array with documents.

// find all that are older then 18
const query = myCollection


A findOne-query has only a single RxDocument or null as result-set.

// find the youngest one
const query = myCollection


Returns a Promise that resolves with the result-set of the query.

const query = myCollection.find();
const results = await query.exec();
console.dir(results); // > [RxDocument,RxDocument,RxDocument..]

Observe $

An BehaviorSubject see that always has the current result-set as value. This is extremely helpfull when used together with UIs that shell always show the same state as what is written in the database.

const query = myCollection.find();
query.$.subscribe(results => {
    console.log('got results: ' + results.length);
// > 'got results: 5'   // BehaviorSubjects emit on subscription

await myCollection.insert({/* ... */}); // insert one
// > 'got results: 6'   // $.subscribe() was called again with the new results


Runs and update on every RxDocument of the query-result.

const query = myCollection.find().where('age').gt(18);
await query.update({
    $inc: {
        age: 1 // increases age of every found document by 1


Deletes all found documents. Returns a promise which resolves to the deleted documents.

// All documents where the age is less than 18
const query = myCollection.find().where('age').lt(18);
// Remove the documents from the collection
const removedDocs = await query.remove();


Here some examples to fast learn how to write queries without reading the docs.

// directly pass search-object
myCollection.find({name: {$eq: 'foo'}})
  .exec().then(documents => console.dir(documents));

// find by using sql equivalent '%like%' syntax
// This example will fe: match 'foo' but also 'fifoo' or 'foofa' or 'fifoofa'
myCollection.find({name: {$regex: '.*foo.*'}})
  .exec().then(documents => console.dir(documents));

// find using a composite statement eg: $or
// This example checks where name is either foo or if name is not existant on the document
myCollection.find({$or: [ { name: { $eq: 'foo' } }, { name: { $exists: false } }})
  .exec().then(documents => console.dir(documents));

// do a case insensitive search
// This example will match 'foo' or 'FOO' or 'FoO' etc...
var regexp = new RegExp('^foo$', 'i');
myCollection.find({name: {$regex: regexp}})
  .exec().then(documents => console.dir(documents));

// chained queries
  .exec().then(documents => console.dir(documents));

NOTICE: RxQuery's are immutable

Because RxDB is a reactive database, we can do heavy performance-optimisation on query-results which change over time. To be able to do this, RxQuery's have to be immutable. This means, when you have a RxQuery and run a .where() on it, the original RxQuery-Object is not changed. Instead the where-function returns a new RxQuery-Object with the changed where-field. Keep this in mind if you create RxQuery's and change them afterwards.


const queryObject = myCollection.find().where('age').gt(18);
// Creates a new RxQuery object, does not modify previous one
const results = await queryObject.exec();
console.dir(results); // result-documents are not sorted by name

const queryObjectSort = queryObject.sort('name');
const results = await queryObjectSort.exec();
console.dir(results); // result-documents are now sorted


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

const is = RxDB.isRxQuery(myObj);

If you are new to RxDB, you should continue here

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