Adding Restaurants to a Map

Another nice feature would be to show the list of restaurants on a map. To map these restaurants, we need to know precisely where the restaurants are. The process of turning an address into a position, as well as turning a position into an address, is known as Geocoding

When geocoding an address, we are often turning the address's text, its street number, and name, along with the city, state, and zip/postal code, into a pair of numbers. These decimal numbers, latitude and longitude describe a single position on the surface of the planet.

Adding columns to store a coordinate

Let's get ready for our geocoding practice by adding columns to our Restaurants table to store these values.

public double Latitude { get; set; }
public double Longitude { get; set; }

Then we will generate a migration for these columns and update the database

dotnet ef migrations add AddLatitudeAndLongitudeToRestaurant

dotnet ef database update

Adding a package to help us geocode

To turn the restaurant's address into a latitude and longitude, we will use a third-party library.

dotnet add package Geocoding.Core

dotnet add package Geocoding.Microsoft

The Geocoding package comes with support for other services other than Microsoft, but this is the one we will use in this lesson. Each of the geocoding systems requires an account and an API key. Microsoft's sign up process is one of the easiest, and we'll choose that to proceed. To sign up for a key, follow these procedures

Similar to our JWT_KEY we will have to add a secret for this API. We'll call the secret BING_MAPS_KEY and access it in our RestaurantsController:

To save the key in secrets:

dotnet user-secrets set "BING_MAPS_KEY" "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx"

Where "xxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxxx" is the key you generated at Microsoft.

NOTE: If you are going to deploy this with Heroku, you'll need to run heroku config:set BING_MAPS_KEY="xxxx" with your specific key in place of xxxx at least once before you deploy.

To access the key from the controller:

private readonly string BING_MAPS_KEY;
// Constructor that receives a reference to your database context
// and stores it in _context_ for you to use in your API methods
public RestaurantsController(DatabaseContext context, IConfiguration config)
{
    _context = context;
    BING_MAPS_KEY = config["BING_MAPS_KEY"];
}

Now that we have added this library and setup an API key, let's add some code to PostRestaurant just before restaurant.UserId = GetCurrentUserId();

// Create a new geocoder
var geocoder = new BingMapsGeocoder(BING_MAPS_KEY);
// Request this address to be geocoded.
var geocodedAddresses = await geocoder.GeocodeAsync(restaurant.Address);
// ... and pick out the best address sorted by the confidence level
var bestGeocodedAddress = geocodedAddresses.OrderBy(address => address.Confidence).LastOrDefault();
// If we have a best geocoded address, use the latitude and longitude from that result
if (bestGeocodedAddress != null)
{
    restaurant.Latitude = bestGeocodedAddress.Coordinates.Latitude;
    restaurant.Longitude = bestGeocodedAddress.Coordinates.Longitude;
}

Let's add some restaurants to our database and see what results we get for geocoded addresses. Enter some restaurants along with addresses you know and then check, using pgcli that there are values for latitude and longitude

Let's also update our exampledata.sql to add geocoded locations for our example restaurants

INSERT INTO "Restaurants" ("Name", "Description", "Address", "Telephone", "Latitude", "Longitude", "UserId") VALUES ('Thoughtbeat', 'Inverse zero administration benchmark', '07 Meadow Vale Drive', '314-651-9791', 27.7970127, -82.6403897, 1);
INSERT INTO "Restaurants" ("Name", "Description", "Address", "Telephone", "Latitude", "Longitude", "UserId") VALUES ('Dabtype', 'Organized stable firmware', '7 Miller Park', '523-760-6681', 27.7970543, -82.6557106, 2);
INSERT INTO "Restaurants" ("Name", "Description", "Address", "Telephone", "Latitude", "Longitude", "UserId") VALUES ('Topdrive', 'Object-based interactive application', '65 Eliot Lane', '650-993-7074', 27.7833108, -82.7159637, 1);
INSERT INTO "Restaurants" ("Name", "Description", "Address", "Telephone", "Latitude", "Longitude", "UserId") VALUES ('Avaveo', 'Persistent zero defect process improvement', '2 Clarendon Junction', '715-663-5265', 27.7717197, -82.6522627, 2);