Concurrency

Author: BenjaminMichaelis

.editorconfig

@@ -125,9 +125,9 @@ csharp_preserve_single_line_blocks = true
 # IntelliTect Conventions     # 
 ###############################
 # var preferences 
-csharp_style_var_for_built_in_types = false:warning
+csharp_style_var_for_built_in_types = false:none
 csharp_style_var_when_type_is_apparent = true:suggestion
-csharp_style_var_elsewhere = false:warning
+csharp_style_var_elsewhere = false:none
 
 ## Naming
 # Style Definitions 

EssentialCSharp.Web/Program.cs

@@ -25,7 +25,7 @@ private static void Main(string[] args)
         builder.Logging.AddConsole();
         builder.Services.AddHealthChecks();
 
-        builder.Services.AddDbContext<EssentialCSharpWebContext>(options => options.UseSqlServer(connectionString));
+        builder.Services.AddDbContextFactory<EssentialCSharpWebContext>(options => options.UseSqlServer(connectionString));
         builder.Services.AddDefaultIdentity<EssentialCSharpWebUser>(options =>
         {
             // Password settings

EssentialCSharp.Web/Services/Referrals/ReferralService.cs

@@ -1,4 +1,4 @@
-using System.Security.Claims;
+using System.Security.Claims;
 using EssentialCSharp.Web.Areas.Identity.Data;
 using EssentialCSharp.Web.Data;
 using Microsoft.AspNetCore.Identity;
@@ -70,9 +70,42 @@ static async Task TrackReferral(EssentialCSharpWebContext dbContext, string refe
             }
             else
             {
-                dbUser.ReferralCount++;
-                await dbContext.SaveChangesAsync();
-                return;
+                bool saved = false;
+                while (!saved)
+                {
+                    try
+                    {
+                        dbUser.ReferralCount++;
+                        await dbContext.SaveChangesAsync();
+                        saved = true;
+                    }
+                    catch (DbUpdateConcurrencyException ex)
+                    {
+                        foreach (var entry in ex.Entries)
+                        {
+                            if (entry.Entity is EssentialCSharpWebUser)
+                            {
+                                var proposedValues = entry.CurrentValues;
+                                var databaseValues = await entry.GetDatabaseValuesAsync();
+
+                                if (databaseValues is not null)
+                                {
+                                    var databaseReferralCount = (int?)databaseValues[nameof(EssentialCSharpWebUser.ReferralCount)];
+                                    proposedValues[nameof(EssentialCSharpWebUser.ReferralCount)] = databaseReferralCount + 1;
+
+                                    // Refresh original values to bypass next concurrency check
+                                    entry.OriginalValues.SetValues(databaseValues);
+                                }
+                            }
+                            else
+                            {
+                                throw new NotSupportedException(
+                                    "Don't know how to handle concurrency conflicts for "
+                                    + entry.Metadata.Name);
+                            }
+                        }
+                    }
+                }
             }
         }
     }