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21:1225 | Id = o.Id; |
21:1226 | DestinationId = o.DestinationId; |
21:1227 | } |
21:1228 | else |
21:1229 | { |
21:1230 | if (o.Price != this.Price) |
21:1231 | this.AddDomainEvent(new PackagePriceChangedEvent( |
21:1232 | Id, o.Price, EntityVersion, EntityVersion+1)); |
21:1233 | } |
21:1234 | Name = o.Name; |
21:1235 | Description = o.Description; |
21:1236 | Price = o.Price; |
21:1237 | DurationInDays = o.DurationInDays; |
21:1238 | StartValidityDate = o.StartValidityDate; |
21:1239 | EndValidityDate = o.EndValidityDate; |
21:1240 | } |
21:1241 | [MaxLength(128)] |
21:1242 | public string Name { get; set; }= null!; |
21:1243 | [MaxLength(128)] |
21:1244 | public string? Description { get; set; } |
21:1245 | public decimal Price { get; set; } |
21:1246 | public int DurationInDays { get; set; } |
21:1247 | public DateTime? StartValidityDate { get; set; } |
21:1248 | public DateTime? EndValidityDate { get; set; } |
21:1249 | public Destination MyDestination { get; set; }= null!; |
21:1250 | [ConcurrencyCheck] |
21:1251 | public long EntityVersion{ get; set; } |
21:1252 | public int DestinationId { get; set; } |
21:1253 | } |
21:1254 | |
21:1255 | The FullUpdate method is the only way to update the IPackage aggregate. When the price changes, add PackagePriceChangedEvent to the entity list of events. |
21:1256 | The MainDBContext.cs file contains the database context definition. It doesn’t inherit from DbContext but from the following predefined context class: |
21:1257 | IdentityDbContext<IdentityUser<int>, IdentityRole<int>, int> |
21:1258 | |
21:1259 | This context defines the user’s tables needed for the authentication. In our case, we opted for the IdentityUser<T> standard and IdentityRole<S> for users and roles, respectively, and used integers for both the T and S entity keys. However, we may also use classes that inherit from IdentityUser and IdentityRole and then add further properties. |
21:1260 | In the OnModelCreating method, we must call base.OnModelCreating(builder) in order to apply the configuration defined in IdentityDbContext. |
21:1261 | MainDBContext implements IUnitOfWork. The following code shows the implementation of all methods that start, roll back, and commit a transaction: |
21:1262 | public async Task StartAsync() |
21:1263 | { |
21:1264 | await Database.BeginTransactionAsync(); |
21:1265 | } |
21:1266 | public Task CommitAsync() |
21:1267 | { |
21:1268 | Database.CommitTransaction(); |
21:1269 | return Task.CompletedTask; |
21:1270 | } |
21:1271 | public Task RollbackAsync() |
21:1272 | { |
21:1273 | Database.RollbackTransaction(); |
21:1274 | return Task.CompletedTask; |
21:1275 | } |
21:1276 | |
21:1277 | However, they are rarely used by command classes in a distributed environment. This is because retrying the same operation until no concurrency exception is returned usually ensures better performance than transactions. |
21:1278 | It is worth analyzing the implementation of the method that passes all changes applied to DbContext to the database: |
21:1279 | public async Task<bool> SaveEntitiesAsync() |
21:1280 | { |
21:1281 | try |
21:1282 | { |
21:1283 | return await SaveChangesAsync() > 0; |
21:1284 | } |
21:1285 | catch (DbUpdateConcurrencyException ex) |
21:1286 | { |
21:1287 | foreach (var entry in ex.Entries) |
21:1288 | { |
21:1289 | entry.State = EntityState.Detached; |
21:1290 | |
21:1291 | } |
21:1292 | throw; |
21:1293 | } |
21:1294 | } |
21:1295 | |
21:1296 | The preceding implementation just calls the SaveChangesAsync DbContext context method, which saves all changes to the database, but then it intercepts all concurrency exceptions and detaches all the entities involved in the concurrency error from the context. This way, the next time a command retries the whole failed operation, their updated versions will be reloaded from the database. |
21:1297 | The Repositories folder contains all repository implementations. It is worth analyzing the implementation of the IPackageRepository.Delete method: |
21:1298 | public async Task<IPackage?> Delete(int id) |
21:1299 | { |
21:1300 | var model = await GetAsync(id); |
21:1301 | if (model is not Package package) return null; |
21:1302 | context.Packages.Remove(package); |
21:1303 | model.AddDomainEvent( |
21:1304 | new PackageDeleteEvent( |
21:1305 | model.Id, package.EntityVersion)); |
21:1306 | return model; |
21:1307 | } |
21:1308 | |
21:1309 | It reads the entity from the database and formally removes it from the Packages dataset. This will force the entity to be deleted from the database when changes are saved to the database. Moreover, it adds PackageDeleteEvent to the aggregate list of events. |
21:1310 | The Extensions folder contains the DBExtensions static class, which, in turn, defines two extension methods to be added to the application DI engine and the ASP.NET Core pipeline, respectively. Once added to the pipeline, these two methods will connect the database layer to the application layer. |
21:1311 | The IServiceCollection extension of AddDbLayer accepts (as its input parameters) the database connection string and the name of the .dll file that contains all migrations. Then, it does the following: |
21:1312 | services.AddDbContext<MainDbContext>(options => |
21:1313 | options.UseSqlServer(connectionString, |
21:1314 | b => b.MigrationsAssembly(migrationAssembly))); |
21:1315 | |
21:1316 | That is, it adds the database context to the DI engine and defines its options – namely, that it uses SQL Server, the database connection string, and the name of the .dll file that contains all migrations. |
21:1317 | Then, it does the following: |
21:1318 | services.AddIdentity<IdentityUser<int>, IdentityRole<int>>() |
21:1319 | .AddEntityFrameworkStores<MainDbContext>() |
21:1320 | .AddDefaultTokenProviders(); |
21:1321 | |
21:1322 | That is, it adds and configures all the types needed to handle database-based authentication and authorization. It adds UserManager, which the application layer can use to manage users. AddDefaultTokenProviders adds the provider that creates the authentication tokens using data contained in the database when users log in. |
21:1323 | Finally, it discovers and adds to the DI engine all repository implementations by calling the AddAllRepositories method, which is defined in the DDD tools we added to the domain layer project. |
21:1324 | The UseDBLayer extension method ensures migrations are applied to the database by calling context.Database.Migrate(), and then it populates the database with some initial objects. In our case, it uses RoleManager and UserManager to create an administrative role and an initial administrator, respectively. Then, it creates some sample destinations and packages. |
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