nuget package
.Net Platforms:
- Framework 4.6.1
- NetStandard 2.0
NHibernate Transaction Awareness Framework
NHibernate Transaction Awareness Framework is implemented by CompileTimeWeaver.Fody
https://nuget.org/packages/CompileTimeWeaver.Fody to gain the best performance. It removes the burden of NHibernate developers of managing sessions and transactions, and domain model validations.
1. Transaction-aware Object
A Transaction-aware Object is a .net object that automatically execute within the scope of a NHibernate session, it participates in an existing or ongoing session, or be the root of a new session. Similar to enterprise component in .net or session bean in EJB, a Transaction-aware Object is a business logic object accessing domain objects (or entity objects). The following example shows a Transaction-aware c# class:
[TransactionAware(DbName="CustomerDb")]
public class MyClass: IDisposable
{
public async Task TravelAllPersonsAsync()
{
var session = TransactionContext.GetCurrentSession("CustomerDb");
var persons = await session.Query<Person>().ToListAsync().ConfigureAwait(false);
foreach (var person in persons)
{
Trace.WriteLine(person.Id + " - " + person.FirstName);
}
}
public void Dispose()
{
//do nothing
}
}
You see there is nothing special except the C# class is decorated by TransactionAwareAttribute. In the TravelAllPersonsAsync() method above, developers can write code to read or write database with NHibernate session without think about when the transaction is commited or when the session is opened/closed, the framework manages the session lift-cycle and transaction lift-cycle automatically.
2. Transaction-aware methods
A method is Transaction-aware method if:
(1) it is a non-static method, and
(2) it is decorated by TransactionAwareAttribute, or the class is decorated by TransactionAwareAttribute.
A Transaction-aware method can either be sync method or async method since version 3.9, and a Transaction-aware method is not thread-safe. A transaction-aware method can call static TransactionContext.GetCurrentSession() method to get current context session, and then take full advantage of NHibernate powers to access database, but a transaction-aware object is not allowed to close context session explicitly. Below is correct code snippet to access database through context session:
ISession session = TransactionContext..GetCurrentSession("CustomerDb");
var user1 = session.Get<User>(1);
user1.Name = "Simon Lu";
session.Update(users);
3. Requirements of a Transaction-aware Object
A transaction-aware object is an instance of an ordinary .net class meeting a few simple requirements:
- Decorated with TransactionAwareAttribute.
- Implement IDisposable interface, the void Dispose() method must exist event though it is empty.
- Call TransactionContext’s methods in transaction-aware methods only.
- Don’t explicitly close session or commit/rollback transaction
4. Transaction
Because framework manages the life-time of transactions, developers don’t need to start a transaction and commit/roolback it in the code. The framework makes the transaction control more easy with these two programming interfaces:
Using AutoComplete
The AutoCompleteAttribute indicates the Debit() method below to abort the transaction if any exception is thrown, and commits the transaction otherwise.
[TransactionAware(DbName="CustomerDb")]
public class Account
{
[AutoComplete]
public virtual void Debit(int amount)
{
// Do some database work. Any exception thrown here aborts the transaction;
// otherwise, transaction commits.
}
}
Voting in an Automatic Transaction
The following code fragment shows the SetAbort and SetComplete methods in use.
//Try to do something crucial to the transaction in progress.
if( !DoSomeWork() )
{
//Something goes wrong.
TransactionContext.SetAbort();
}
else
{
//All goes well.
TransactionContext.SetComplete();
}
SetComplete indicates that your method votes to commit its work; SetAbort indicates that your object encountered a problem and votes to abort the ongoing transaction, a single abort vote from any method participating in the transaction causes the entire transaction to fail.
The absence of an explicit vote in a method means the database update in the method accumulate the context transaction without commit or rollback. If there is not explicit vote during the life-cycle of the owner of a context session, the context transaction is rollback when the owner is disposed, other than that, a context transaction is neither committed nor aborted until a transaction-aware method explicitly vote.
5. Join existing session or open new session
[TransactionAware(DbName="your_database_name", TransactionAwareOption = TransactionAwareOption.Required)]
public class MyClass: IDisposable
{
...
}
When applying the TransactionAwareAttribute, you can set TransactionAwareOption property to control if the object joins existing session or open a new session.
TransactionAwareOption.Required (default)
Indicates that the object requires a session. It runs in the scope of an existing session, if one exists. If no session exists, the object starts one.TransactionAwareOption.RequiresNew
Indicates that the object requires a new session.
6. Object Injection
A Transaction-aware object can inject objects as its properties or fields by declare the properties/fields with InjectedOnCreatedAttribute, and transparently dispose them when it is disposed. This open the door for developers to inject Transaction-aware objects into the other Transaction-aware object so that they can share the same database session. Below is an example class, and instances of EntityRepository is created and injected as private field _entityRepository, and it is disposed automatically even though the Dispose method body is empty.
[TransactionAware(DbName="your_database_name")]
public class TransactionAwareUnitOfWork : IDisposable
{
[InjectedOnCreated]
private EntityRepository _entityRepository;
...
public void Dispose()
{
//Transaction Awareness framework will automatically dispose all injected objects
}
}
7. Practice
Prerequisite: domain classes and mapping classes are ready.
Step 1) Download and add NuGet package CompileTimeAOP.TransactionAwareness to your c# project.
Step 2) Add a Transaction-aware class to your project
using CompileTimeAOP.Transaction;
[TransactionAware(DbName="your_database_name")]
public class MyClass: IDisposable
{
public async Task TravelAllPersonsAsync()
{
var session = TransactionContext.GetCurrentSession("your_database_name");
var persons = await session.Query<Person>().ToListAsync().ConfigureAwait(false);
foreach (var person in persons)
{
Trace.WriteLine(person.Id + " - " + person.FirstName);
}
}
public void Dispose()
{
//do nothing
}
}
Step 3) Add this code snippet into application startup code to setup database connection
using CompileTimeAOP.Transaction;
DbSessionFactory.Create("your_database_name",
"hibernate.yourdb.config",
fluentCfg =>
{
fluentCfg.Mappings(m =>
{
m.FluentMappings.AddFromAssemblyOf<YourFluentNHibernateMapClass>();
});
fluentCfg.ExposeConfiguration(cfg => new NHibernate.Tool.hbm2ddl.SchemaUpdate(cfg).Execute(false, true));
});
Step 4) Use Transaction-aware class
using (var testObj = new MyClass())
{
await testObj.TravelAllPersonsAsync();
}
8. Multiple Database
Sometimes it is necessary for a Transaction-aware object to access two databases in one method, for example, an online shopping cart object updates transaction database and access customer service database in its PlaceOrder () method. Transaction-awareness framework let it do it easily by decorating the PlaceOrder method with two TransactionAwareAttribute with different database names as constructor parameter. See it below:
[TransactionAware("TransactionDb"]
public class OnlineShoppingStore: IDisposable
{
[TransactionAware("CustomerDb"]
[AutoComplete]
public void PlaceOrder(OrderDto order)
{
var customerDbSession = TransactionContext.GetCurrentSession("CustomerDb");
var customer = customerDbSession.Query<CustomerEntity>(order.CustomerId);
...
var transDbSession = TransactionContext.GetCurrentSession("TransactionDb");
transDbSession.Save(new OrderEntity(){...});
}
...
}
The framework comes with out-of-the-box Distributed-transaction feature, in the PlaceOrdermethod above, it puts two database update in one distributed transaction so that the integrity accross multi-database is guaranteed.
Notes:
- use
TransactionContext.GetCurrentSession(string dbName) to get database sessions from different database where multiple databases exist.
- Call
DbSessionFactory.Create() for each database with different database names to setup connection.
- Distributed-transaction needs DTS Windows service, you may change firewall settings if two database servers are on different computers. (study how to setup DTS on two servers)
9. Fluent Validation
Transaction-aware framework offers developers out-of-the-box FluentValidation feature to guarantee the integrity of domain model whenever there is database update. It allows to put all model validation rules in different assembly to avoid domain model polution.
Usage:
- Create a C# project to contain all the FluentValidation validators.
- Add all validators to validate entity classes, for example, the PersonValidator class below to validate Person entity class:
using FluentValidation;
public class PersonValidator : AbstractValidator<Person>
{
public PersonValidator()
{
RuleFor(x => x.Id).NotEmpty();
RuleFor(x => x.FirstName).NotNull().Length(1, 10);
}
}
- Add validator assembly,
typeof (PersonValidator).Assembly, to the call to DbSessionFactory.Create() as the last parameter, the framework validates entity objects once there is update on them, and throws FluentValidation.ValidationException exception if there is any break to validation rules.
DbSessionFactory.Create("your_database_name",
"hibernate.yourdb.config",
fluentCfg =>
{
fluentCfg.Mappings(m =>
{
m.FluentMappings.AddFromAssemblyOf<YourFluentNHibernateMapClass>();
});
fluentCfg.ExposeConfiguration(cfg => new NHibernate.Tool.hbm2ddl.SchemaUpdate(cfg).Execute(false, true));
},
typeof (PersonValidator).Assembly);
