Result Sets

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      Description — How to use Couchbase Lite Query’s Result Sets
      Related Content — QueryBuilder | SQL++ for Mobile | Predictive Queries | Live Queries | Indexing

      Query Execution

      The execution of a Couchbase Lite for Java’s database query returns an array of results, a result set.

      Each row of the result set represents the data returned from a document that met the conditions defined by the WHERE statement of your query. The composition of each row is determined by the SelectResult expressions provided in the SELECT statement.

      Returned Results

      The types of SelectResult formats you may encounter include those generated by :

      Return All Document Properties

      The SelectResult returned by SelectResult.all is a dictionary object, with the database name as the key and the document properties as an array of key-value pairs

      Example 1. Returning All Properties
      [
        {
          "travel-sample": { (1)
            "callsign": "MILE-AIR",
            "country": "United States",
            "iata": "Q5",
            "icao": "MLA",
            "id": 10,
            "name": "40-Mile Air",
            "type": "airline"
          }
        },
        {
          "travel-sample": { (2)
            "callsign": "ALASKAN-AIR",
            "country": "United States",
            "iata": "AA",
            "icao": "AAA",
            "id": 10,
            "name": "Alaskan Airways",
            "type": "airline"
          }
        }
      ]

      Return Document Id Only

      The SelectResult returned by queries using a SelectResult expression of the form SelectResult.expression(meta.id) comprises a dictionary object with ID as the key and the ID value as the value.

      Example 2. Returning Meta Properties — Document ID
      [
        {
          "id": "hotel123"
        },
        {
          "id": "hotel456"
        },
      ]

      Return Specific Properties Only

      The SelectResult returned by queries using one or more SelectResult expressions of the form SelectResult.expression(property("name")) ) comprises a key-value pair for each SelectResult expression in the query. The key being the property name.

      Example 3. Returning Specific Properties
      [
        { (1)
          "id": "hotel123",
          "type": "hotel",
          "name": "Hotel Ghia"
        },
        { (2)
          "id": "hotel456",
          "type": "hotel",
          "name": "Hotel Deluxe",
        }
      ]

      Processing Results

      To retrieve the results of your query, you need to execute it using Query.execute.

      The output from the execution is an array, with each array element representing the data from a document that matched your search criteria.

      To unpack the results you need to iterate through this array. Alternatively, you can convert the result to a JSON string — see:

      Access Document Properties - All Properties

      Here we look at how to access document properties when you have used SelectResult.all.

      In this case each array element is a dictionary structure with the database name as its key. The properties are presented in the value as an array of key-value pairs (property name/property value).

      You access the retrieved document properties by converting each row’s value, in turn, to a dictionary — as shown in Example 4.

      Example 4. Access All Properties
      try {
          for (Result result : listQuery.execute().allResults()) {
                           // get the k-v pairs from the 'hotel' key's value into a dictionary
              thisDocsProps = result.getDictionary(0)); (1)
              thisDocsId = thisDocsProps.getString("id");
              thisDocsName = thisDocsProps.getString("Name");
              thisDocsType = thisDocsProps.getString("Type");
              thisDocsCity = thisDocsProps.getString("City");
      
              // Alternatively, access results value dictionary directly
              final Hotel hotel = new Hotel();
              hotel.Id = result.getDictionary(0).getString("id"); (2)
              hotel.Type = result.getDictionary(0).getString("Type");
              hotel.Name = result.getDictionary(0).getString("Name");
              hotel.City = result.getDictionary(0).getString("City");
              hotel.Country= result.getDictionary(0).getString("Country");
              hotel.Description = result.getDictionary(0).getString("Description");
              hotels.put(hotel.Id, hotel);
      
          }
      } catch (CouchbaseLiteException e) {
          e.printStackTrace();
      }
      1 Here we get the dictionary of document properties using the database name as the key. You can add this dictionary to an array of returned matches, for processing elsewhere in the app.
      2 Alternatively you can access the document properties here, by using the property names as keys to the dictionary object.

      Access Document Properties - ID

      Here we look at how to access document properties when you have returned only the document IDs for documents that matched your selection criteria.

      This is something you may do when retrieval of the properties directly by the query may consume excessive amounts of memory and-or processing time.

      In this case each array element is a dictionary structure where ID is the key and the required document ID is the value.

      Access the required document properties by retrieving the document from the database using its document ID — as shown in Example 5.

      Example 5. Access by ID
      
      try {
          for (Result result : listQuery.execute().allResults()) {
      
              // get the ID form the result's k-v pair array
              thisDocsId = result.getString("metaID"); (1)
      
              // Get document from DB using retrieved ID
              Document thisDoc = this_Db.getDocument(thisDocsId);
      
              // Process document as required
              thisDocsName = thisDoc.getString("Name");
      
          }
      } catch (CouchbaseLiteException e) {
          e.printStackTrace();
      }
      1 Extract the Id value from the dictionary and use it to get the document from the database

      Access Document Properties - Selected Properties

      Here we look at how to access properties when you have used SelectResult to get a specific subset of properties.

      In this case each array element is an array of key value pairs (property name/property value).

      Access the retrieved properties by converting each row into a dictionary — as shown in [ex-acc-specific].

      
      try {
          for (Result result : listQuery.execute().allResults()) {
      
              // get data direct from result k-v pairs
              final Hotel hotel = new Hotel();
              hotel.Id = result.getString("id");
              hotel.Type = result.getString("Type");
              hotel.Name = result.getString("Name");
              hotel.City = result.getString("City");
      
              // Store created hotel object in a hashmap of hotels
              hotels.put(hotel.Id, hotel);
      
              // Get result k-v pairs into a 'dictionary' object
              Map <String, Object> thisDocsProps = result.toMap();
              thisDocsId =
                      thisDocsProps.getOrDefault("id",null).toString();
              thisDocsName =
                      thisDocsProps.getOrDefault("Name",null).toString();
              thisDocsType =
                      thisDocsProps.getOrDefault("Type",null).toString();
              thisDocsCity =
                      thisDocsProps.getOrDefault("City",null).toString();
      
          }
      } catch (CouchbaseLiteException e) {
          e.printStackTrace();
      }

      JSON Result Sets

      Example 6. Using JSON Results

      Use Result.toJSON() to transform your result string into a JSON string, which can easily be serialized or used as required in your application. See <> for a working example.

      // Uses Jackson JSON processor
      
      ArrayList<Hotel> hotels = new ArrayList<Hotel>();
      HashMap<String, Object> dictFromJSONstring;
      for (Result result : listQuery.execute()) {
      
        // Get result as JSON string
        String thisJsonString = result.toJSON(); (1)
      
              // Get Java  Hashmap from JSON string
        HashMap<String, Object> dictFromJSONstring =
                mapper.readValue(thisJsonString, HashMap.class); (2)
      
      
        // Use created hashmap
        String hotelId = dictFromJSONstring.get("id").toString();
        String hotelType = dictFromJSONstring.get("type").toString();
        String hotelname = dictFromJSONstring.get("name").toString();
      
      
        // Get custom object from Native 'dictionary' object
        Hotel thisHotel =
                mapper.readValue(thisJsonString, Hotel.class); (3)
        hotels.add(thisHotel);
      
      }
      1 Get the Query result as a JSON string — see JSON String Format
      2 Get a native object from the JSON string
      3 Populate your custom object from the dictionary created from JSON data
      JSON String Format

      If your query selects ALL then the JSON format will be:

      {
        database-name: {
          key1: "value1",
          keyx: "valuex"
        }
      }

      If your query selects a sub-set of available properties then the JSON format will be:

      {
        key1: "value1",
        keyx: "valuex"
      }