My app is very basic (write it fast, run it once, then forget), so a solution to the problem above was to simply introduce lock around the section that was doing multi-table inserts.
public void CallGooglePlacesAPIAndSetCallback(string websiteName) { using (var db = new WebAnalyzerEntities()) { IList<IRecord> addressesToBeSearched = db.Rent.Where<IRecord>(o => o.Url.Contains(websiteName) && o.SpatialAnalysis.Count == 0).ToList().Union(db.Sale.Where<IRecord>(oo => oo.Url.Contains(websiteName) && oo.SpatialAnalysis.Count == 0)).ToList(); foreach (var locationTobeSearched in addressesToBeSearched) { try { //this is where I introduced the lock lock (_lock) { dynamic res = null; using (var client = new HttpClient()) { while (res == null || HasProperty(res, "next_page_token")) { var url = $"https://maps.googleapis.com/maps/api/geocode/json?address={locationTobeSearched.Address}&key={googlePlacesApiKey}&bounds=51.222,-11.0133788|55.636,-5.6582363"; if (res != null && HasProperty(res, "next_page_token")) url += "&pagetoken=" + res["next_page_token"]; var response = client.GetStringAsync(url).Result; JavaScriptSerializer json = new JavaScriptSerializer(); res = json.Deserialize<dynamic>(response); if (res["status"] == "OK") { Tuple<decimal?, decimal?, string> coordinatesAndPostCode = ReadResponse(res["results"][0]); if (coordinatesAndPostCode != null && coordinatesAndPostCode.Item1.HasValue && coordinatesAndPostCode.Item2.HasValue) { //this is the line where exception was thrown locationTobeSearched.SpatialAnalysis.Add(new SpatialAnalysis() { Point = CreatePoint(coordinatesAndPostCode.Item1.Value, coordinatesAndPostCode.Item2.Value) }); locationTobeSearched.PostCode = coordinatesAndPostCode.Item3; } } else if (res["status"] == "OVER_QUERY_LIMIT") { return; } } } } } catch (Exception e) { } db.SaveChanges(); } } }