--- title: Query pubDate: 2026-08-17T09:53:44.266Z antora: editUrl: https://github.com/couchbaselabs/mobile-travel-sample/edit/master/content/modules/mobile-travel-tutorial/pages/swift/develop/query.adoc xref: xref:tutorials:mobile-travel-tutorial:swift/develop/query.adoc[] --- [Consult the llms.txt file for a full list of contents](/llms.txt) [View original HTML](/tutorials/mobile-travel-tutorial/swift/develop/query.html) # Query ## [](#overview)Overview Couchbase Lite \[[1](#%5Ffootnotedef%5F1 "View footnote.")\] includes support for N1QL like query interface. Database can be queried by constructing a query using a Query builder and then executing that query. The Query interface in Couchbase Lite 2.0 is powerful and includes support for the following among others * Pattern Matching * Regex Matching * Math Functions * String Manipulation Functions * Aggregate Functions * Grouping * Joins (within single database) * Sorting * NilOrMissing properties ### [](#implementation-pattern)Implementation Pattern The `select` clause and `where` clause in the `Query` statement require a `CouchbaseLite.Expression` type. Consider the following query. ```swift let hotelSearchQuery = Query .select(SelectResult.expression(Meta.id), SelectResult.expression(Expression.property("name"))) .from(DataSource.database(db)) .where( Expression.property("description").like("%\(descriptionStr)%") .and(Expression.property("type").equalTo("hotel")) .and(Expression.property("country").equalTo(locationStr) .or(Expression.property("city").equalTo(locationStr)) .or(Expression.property("state").equalTo(locationStr)) .or(Expression.property("address").equalTo(locationStr))) ) ``` Often times, the same `Expression` may be required across multiple queries. This can quickly become tedious and difficult to maintain. The recommended pattern is to define constants corresponding to the Expressions and to reuse them across queries. Open the [QueryConsts.swift](https://github.com/couchbaselabs/mobile-travel-sample/blob/master/ios/TravelSample/TravelSample/Utilities/QueryConsts.swift#L15)file. This file defines the CouchbaseLite expressions that are used in the Travel App ```swift struct _Property { // Query: Property Expressions static let DOCID = Meta.id static let TYPE = Expression.property("type") static let USERNAME = Expression.property("username") static let FLIGHTS = Expression.property("flights") static let DESCRIPTION = Expression.property("description") static let NAME = Expression.property("name") static let COUNTRY = Expression.property("country") static let CITY = Expression.property("city") static let STATE = Expression.property("state") static let ADDRESS = Expression.property("address") static let FAA = Expression.property("faa") static let ICAO = Expression.property("icao") static let AIRPORTNAME = Expression.property("airportname") } struct _SelectColumn { // Query: Select Results static let NAMERESULT = SelectResult.expression(_Property.NAME) static let AIRPORTNAMERESULT = SelectResult.expression(_Property.AIRPORTNAME) static let FLIGHTSRESULT = SelectResult.expression(_Property.FLIGHTS) static let DOCIDRESULT = SelectResult.expression(_Property.DOCID) static let COUNTRESULT = SelectResult.expression(Function.count(1)) static let ALLRESULT = SelectResult.all() } ``` ## [](#simple-query)Simple Query The travel app has many instances of querying the database. We will discuss a simple example here. **Open the file** `AirportPresenter.swift`. We will review the `fetchAirportsMatching` method. [AirportPresenter.swift](https://github.com/couchbaselabs/mobile-travel-sample/blob/master/ios/TravelSample/TravelSample/Presenter/AirportPresenter.swift#L28) ```swift func fetchAirportsMatching( _ searchStr:String, handler:@escaping(_ airports:Airports?, _ error:Error?)->Void) { ... } ``` There are 3 different queries in this function body. The query that is ran depends on the length of the search term. You can ignore this specificity, in this section we will look at the 3rd query. The query below **selects** the "name" property in documents **from** the database **where** the **type** property is equal to **airport** and the "airportname" property is equal to the search term. ```swift searchQuery = QueryBuilder .select(_SelectColumn.AIRPORTNAMERESULT) .from(DataSource.database(db)) .where(_Property.TYPE .equalTo(Expression.string("airport")) .and (Expression.property("airportname") .like(Expression.string("\(searchStr)%")))) ``` Next, the query is executed using the `execute()` method. Each row in the result will contain a single property called "airportname". The final result is passed to the `handler` callback where the result will be displayed in a `TableView`. ```swift if let searchQuery = searchQuery { var matches:Airports = [] do { for row in try searchQuery.execute() { if let match = row.string(forKey: "airportname") { matches.append( match) } } handler(matches,nil) } catch { handler(nil,error) } } ``` Try it out — Simple Query 1. Log into the Travel Sample Mobile app as "demo" user and password as "password" 2. Tap on "+"" button to make a flight reservation 3. In the "From" airport textfield, enter "DTW"" 4. Verify that the first item in the drop down list is "Detroit Metro Wayne Co"" ![ios simple query](../../_images/ios_simple_query.gif) ## [](#advanced-query)Advanced Query In this section we will discuss the JOIN query; intra-database joins. If you recall from the Data Modeling section, the document with a **type** equal to "bookmarkedhotels" contains a **hotels** property which is an array of IDs of bookmarked hotels. ```json { "_id": "hotel1", "name": "San Francisco Hotel", "address": "123, Park Street, San Francisco" } { "type": "bookmarkedhotels", "hotels": ["hotel1", "hotel2"] } ``` We will review the query that fetches documents whose `_id` is included in the "hotels" property array of the document of type "bookmarkedhotels". **Open the file** `HotelPresenter.swift`. We will review the `fetchBookmarkedHotels` method. [HotelPresenter.swift](https://github.com/couchbaselabs/mobile-travel-sample/blob/master/ios/TravelSample/TravelSample/Presenter/HotelPresenter.swift#L154) ```swift func fetchBookmarkedHotels( handler:@escaping(_ hotels:Hotels?, _ error:Error?)->Void) { ... } ``` First, we instantiate two data sources which corresponds to the two sides of the join query. ```swift let bookmarkDS = DataSource.database(db).as("bookmarkDS") let hotelsDS = DataSource.database(db).as("hotelsDS") ``` Next we write the query expressions. The first one gets the `hotels` property on the bookmarks data source. The seconds get the document ID on the hotels data source. ```swift let hotelsExpr = Expression.property("hotels").from("bookmarkDS") let hotelIdExpr = Meta.id.from("hotelsDS") ``` Next, we use a function expression to find document's whose `\_id` property is in the `hotels` array. And build the join expression. ```swift let joinExpr = ArrayFunction.contains(hotelsExpr, value: hotelIdExpr) let join = Join.join(hotelsDS).on(joinExpr); ``` Finally, the query object uses that join expression to find all the hotel document referenced in the "hotels" array of the bookmark document. ```swift let typeExpr = Expression.property("type").from("bookmarkDS") let bookmarkAllColumns = _SelectColumn.ALLRESULT.from("bookmarkDS") let hotelsAllColumns = _SelectColumn.ALLRESULT.from("hotelsDS") let query = QueryBuilder.select(bookmarkAllColumns, hotelsAllColumns) .from(bookmarkDS) .join(join) .where(typeExpr.equalTo(Expression.string("bookmarkedhotels"))); ``` And we use the `execute()` method to get the results back pass them on to the view. ```swift for result in try query.execute() { if let hotel = result.dictionary(forKey: "hotelsDS")?.toDictionary() as? Hotel{ bookmarkedHotels.append(hotel) } } handler(bookmarkedHotels,nil) ``` Try it out — Advanced Query 1. Log into the Travel Sample Mobile app as "Guest" user by selecting "Proceed as Guest" 2. Tap on "Hotels"" button 3. In the "Description" text field, enter "pets" 4. In the "Location" text field, enter "London" 5. Verify that you see the "Novotel London West" listed 6. Swipe left to "bookmark" the hotel 7. Tap "Cancel" button 8. Verify that the Novotel hotel that you bookmarked earlier shows up in the list ![ios join query](../../_images/ios_join_query.gif) --- [1](#%5Ffootnoteref%5F1). 2.0+