A location-aware user database implemented using Google S2 Geometry and Hashicorp's go-memdb (insert/update operations)

operations.go

package store

import (
	"github.com/golang/geo/s1"
	"github.com/golang/geo/s2"
	"github.com/hashicorp/go-memdb"
)

// Insert adds a new user to th
func (s *Store) Insert(user int, lat float64, lon float64) error {
	// Initialize write transaction.
	txn := s.db.Txn(true)
	err := txn.Insert("users", &User{
		ID:     user,
		CellID: s2.CellIDFromLatLng(s2.LatLngFromDegrees(lat, lon)).String(),
	})
	// Abort transaction on error.
	if err != nil {
		txn.Abort()
		return err
	}
	// Commit changes in order to complete the transaction.
	txn.Commit()
	return nil
}

// Near returns a set of users that are located with the specified radius around the provided lat/lon.
func (s *Store) Near(lat float64, lon float64, radius int) ([]User, error) {

	// Create region around the provided point.
	// First, create a cap on the earth sphere with the required area (based on center & radius).
	// Cap is determined based on the provided point and the cap angle (derived from capRadius/earthRadius)
	angle := s1.Angle(float64(radius) / 6371000)
	sphereCap := s2.CapFromCenterAngle(s2.PointFromLatLng(s2.LatLngFromDegrees(lat, lon)), angle)
	r := s2.Region(sphereCap)
	// Get the CellUnion representing the specified area.
	covering := s.coverer.Covering(r)

	// Find users in each of the cells in a single transaction.
	txn := s.db.Txn(false)
	var users []User
	for _, cell := range covering {
		// MemDB supports prefix indexing without explicit definition.
		iter, err := txn.Get("users", "cellID_prefix", cell.String())
		if err != nil {
			continue
		}

		user := iter.Next()
		for {
			if user == nil {
				break
			}

			// Process user..
			user = iter.Next()
		}
	}

	return users, nil
}