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September 17, 2020

Building Map Interface Apps using a Geo JSON GraphQL API

Sebastian Scholl
@SebScholl

Developing apps that rely on geo-coordinates to enable important features must go far beyond simply storing latitude and longitude data. Geo coordinate algorithms that calculate bounds and distances can be a fun brain challenge to implement, though more often than not they become time-consuming distractions from one's core project.

In this tutorial, we’re going to look at how we can quickly set up and use an API that has advanced and ready to use Geo Coordinate operations. It doesn’t matter whether you are building a real estate application that’s map-based, a food reviews site that shows the distance a user is from the restaurant, or any other app that will need to work with geo-coordinate data; this tutorial will apply to any such use case.

That said, we’re going to use the example of a food reviews app that needs to show user’s the distance they are from a reviewed restaurant. So let’s do it!

Tutorial

To start, you’re going to need an 8base Workspace. The free plan will work just fine for this tutorial, so go ahead and sign up at app.8base.com if you haven’t already.

Once logged into 8base, we’re going to want to set up a simple data model for our reviews. It’s going to look like this:

Restaurants

  • name: Text
  • location: Geo
  • Reviews: has_many Reviews

Reviews

  • content: Text
  • rating: Number
  • Restaurant: has_one Restaurants

Importing the Data Model and Seed Data

You’re welcome to quickly construct this data model using the 8base data builder. However, I'd recommend importing the schema and seed data using the CLI. It will not only quickly set up the data model but also populate the database with 20 restaurants and 40 reviews.

The following commands will quickly get you up and running! You'll want to feed the last import command a path to this file.

{% code-block language="shell" %}
# Install the cli
npm install -g 8base-cli
# Authenticate the CLI
8base login
# Create an empty 8base project and select workspace
8base init rr-tutorial -e
# Import the schema
8base import -f [PATH_TO schema-and-data.json]
{% code-block-end%}

At this point, the data model should be set up and the seed data ready to use! You can hop back into the 8base console and look at the Data Builder/Viewer to see the imported schema and records. It will look like the screenshot below.

8base data viewer with imported records
8base data viewer with imported records

Reviewing the Saved Location Data

If you look at the Restaurants table, you'll see there is a field called location that has the type Geo selected with the format set to Point. Geo Points are simply a latitude and longitude coordinate that together references a specific point on the map.

Now switch over to the Data tab and you'll see the Location column displaying all the latitude and longitude coordinates in arrays. This is how the API received the data, though when editing a record via the UI 8base separates the two values.

Editing latitude and longitude fields in 8base console
Editing latitude and longitude fields in 8base console

With this GraphQL API being auto-generated by 8base, all our geo coordinate operations are ready to be used. So let's pop over to the API Explorer to see what kind of queries and mutations we have access to.

Writing Queries with Geo Filtering

There are many methods to get a user's current location when they are using your app or website. For example, many modern browsers have implemented the Geolocation API that prompts the user for permission to access their current location. When granted, the following code snippet would return the user's location using geo coordinates.

{% code-block language="js" %}
navigator.geolocation.getCurrentPosition(
 ({ coords: { latitude, longitude } }) => console.log([latitude, longitude])
)
{% code-block-end %}

Using the returned latitude and longitude, you'll be able to pass the user's location as an argument to your GraphQL query. We just happen to be working with a user's current location in this example. Any valid geo coordinates could be passed to a query for use in filtering, depending on the use case.

So, let's go ahead and write a query that allows us the filter by the distance a Restaurant is from the user's current location, using meters. We're going to manually set the user's current location to latitude 40.748981˚ longitude -73.985910˚, which is roughly the Empire State Building in New York City.

Spoiler Alert: The restaurant data is all of the places in Manhattan!

In the API Explorer, open up the Variables input and paste in the following JSON blob. The top-level keys we'll be able to use as arguments in the query editor.

{% code-block language="json" %}
{
 "distance": 2500,
 "userLocation": {
   "type": "Point",
   "coordinates": [40.748981, -73.98591]
 }
}
{% code-block-end %}

Now we'll write out our actual query. See it below and read the in code comments for context!

{% code-block language="js" %}
query(
 # Set arguments with specified required types
 $userLocation: GeometryInput!
 $distance: Float!
) {
 # User restaurantsList query with filter
 restaurantsList(
   filter: {
     location: {
       # When filtering on a Geo type Field, we can use the Distance predicate.
       distance: {
         # Specify the users current location (argument format)
         from: $userLocation
         unit: meters
         value: {
           # Get results LESS THAN OR EQUAL TO (lte) the specified distance
           lte: $distance
         }
       }
     }
   }
 ) {
   count
   items {
     name
     location {
       coordinates
     }
   }
 }
}
{% code-block-end %}

Run the query and BOOM...we're in business! Well, not exactly.

Filtering records by distance from a lat-long point
Filtering records by distance from a lat-long point

We can see that from our given userLocation, 6 restaurants were within 2500 meters. However, we only filtered the list and in the response got back geo coordinates. What we need is to get back the actual distance calculation from our user!

Using ExtraFields to Return Distance Calculations

We'll be able to accomplish this using an API feature called extraFields. Essentially, what we're going to do is return a calculated result that's not a part of our core data model. This is what extraFields enables us to do.

Let's re-work our query a bit to accomplish this requirement. Just like last time, see it below and read the in-code comments for context!

{% code-block language="js" %}
query(
 # Set the same arguments with specified required types
 $userLocation: GeometryInput!
 $distance: Float!
) {
 # User restaurantsList query with filter and extraFields
 restaurantsList(
   extraFields: {
     # Specify which field the "extra field" will be calculated from
     location: {
       # Give the new field a unique name
       as: "distanceFromUser"
       fn: {
         # Declare the function calculate that will be used. In this case, distance from the userLocation using meters.
         distance: { from: $userLocation, unit: meters }
       }
     }
   }
   filter: {
     # Instead of repeating ourselves in the filter, we can filter using the extraField that's getting calculated!
     _extraField: {
       # Specify the extraField we're filtering by.
       alias: "distanceFromUser"
       # Declare the field type and relevant predicate. In this case, a float less than the specified distance.
       float: { lt: $distance }
     }
   }
 ) {
   count
   items {
     name
     # extraFields can then be collected in the response like so.
     _extraFields {
       distanceFromUser: Float
     }
   }
 }
}
{% code-block-end %}

Pretty cool! Right? As you can see in your response, you're now getting back the user's precise distance from the different restaurant locations in meters.

Using extraFields distances with lat long points
Using extraFields distances with lat long points

Adding Grouping and Aggregation to the Query

As you can imagine, the $distance can be adjustable by your user in the UI. For example, they may select 1km, 5km, or 10km as the distance while using the app and then the query would run and filter accordingly. That said, other types of data can get generated in conjunction with the geocoordinate filters we just explored.

For example, what if the user not only wanted to see restaurants within 2500 meters but also wanted to see the average rating from reviews? How could that be accomplished?

Well, by diving into the groubBy feature of the API we'd be able to accomplish this next level of complexity. Let's take a look!

{% code-block language="js" %}
query(
 # Set arguments with specified required types
 $userLocation: GeometryInput!
 $distance: Float!
) {
 # User restaurantsList query with filter
 restaurantsList(
   extraFields: {
     # Specify which field the "extra field" will be calculated from
     location: {
       # Give the new field a unique name
       as: "distanceFromUser"
       fn: {
         # Declare the function calculate that will be used. In this case, distance from the userLocation using meters.
         distance: { from: $userLocation, unit: meters }
       }
     }
   }
   filter: {
     # Instead of repeating ourselves in the filter, we can filter using the extraField that's getting calculated!
     _extraField: {
       # Specify the extraField we're filtering by.
       alias: "distanceFromUser"
       # Declare the field type and relevant predicate. In this case, a float less than the specified distance.
       float: { lt: $distance }
     }
   }
 ) {
   count
   items {
     name
     _extraFields {
       distanceFromUser: Float
     }
     # In the response we specify a groupBy argument to the relation
     reviews(
       groupBy: {
         query: {
           # On the ratings field, we aggregate an average of the reviews belonging to a restaurant.
           rating: { as: "avgRating", fn: { aggregate: AVG } }
           # We alias the grouping as reviews
           _group: { as: "reviews" }
         }
       }
     ) {
       groups {
         # In each group, we return the avgRating as a float
         avgRating: Float
         # We return the "items" (reviews) with content and the individual rating
         reviews: ReviewGroup {
           items {
             content
             rating
           }
         }
       }
     }
   }
 }
}
{% code-block-end %}

An example of the expected response is below.

{% code-block language="js" %}
{
 "data": {
   "restaurantsList": {
     "count": 6,
     "items": [
       {
         "name": "The Burrito Box",
         "_extraFields": {
           "distanceFromUser": 2149.482589321746
         },
         "reviews": {
           "groups": [
             {
               "avgRating": 4,
               "reviews": {
                 "items": [
                   {
                     "content": "I liked it!",
                     "rating": 4
                   },
                   {
                     "content": "It was okay.",
                     "rating": 4
                   }
                 ]
               }
             }
           ]
         }
       },
       {
         "name": "Chick'nCone",
         "_extraFields": {
           "distanceFromUser": 2101.9531673470437
         },
         "reviews": {
           "groups": [
             {
               "avgRating": 4.5,
               "reviews": {
                 "items": [
                   {
                     "content": "It was okay.",
                     "rating": 4.5
                   },
                   {
                     "content": "I liked it!",
                     "rating": 4.5
                   }
                 ]
               }
             }
           ]
         }
       }
       // ... more!
     ]
   }
 }
}
{% code-block-end %}

Final Thoughts

As demonstrated, using an existing API platform we're able to quickly standup an extremely powerful API that has advanced geo coordinate operations built into it. This can apply to a large variety of applications that you maybe building.

I hope that you found this useful and interesting! Please let us know if you have any questions, as well as what projects you end up building using 8base!

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