Synopse

To content | To menu | To search

Tag - EntityObject

Entries feed

2015, Monday May 18

CQRS Persistence Service of any DDD object with mORMot

We introduced DDD concepts some time ago, in a series of articles in this blog.
At that time, we proposed a simple way of using mORMot types to implement DDD in your applications.
But all Domain Entitities being tied to the framework TSQLRecord class did appear as a limitation, breaking the Persistence Ignorance principle, since it couples the DDD objects to the framework implementation details.

We introduced a new mORMotDDD.pas unit, which is able to easily create CQRS Persistence services for any plain Delphi class (the famous PODOs - Plain Old Delphi Objects).
No need to inherit from TSQLRecord, or pollute your class definition with attributes!

For instance, a TUser class may be persisted via such a service:

type
  IDomUserCommand = interface(IDomUserQuery)
    ['{D345854F-7337-4006-B324-5D635FBED312}']
    function Add(const aAggregate: TUser): TCQRSResult;
    function Update(const aUpdatedAggregate: TUser): TCQRSResult;
    function Delete: TCQRSResult;
    function Commit: TCQRSResult;
  end;

Here, the write operations are defined in a IDomUserCommand service, which is separated (but inherits) from IDomUserQuery, which is used for read operations.
Separating reads and writes is a powerful pattern also known as CQRS, i.e. Command Query Responsibility Segregation, which we followed when defining our persistence services.
The framework make it pretty easy to create such services for storing any kind of class type in any SQL or NoSQL engine, with almost no code to write.
Last but not least, using such interface-based services for data persistence will allow to stub or mock the data access layer, making unit testing straightforward: you would not fear to write TDD code any more!

Please refer to our updated documentation for this unique and powerful feature.
You may take a look at the corresponding dddDomUserTypes.pas, dddDomUserCQRS.pas, and dddInfraRepoUser.pas units, detailed as sample reference.
Feedback is welcome in our forum, as usual!

2014, Sunday June 22

Audit-trail for ORM change tracking

Since most CRUD operations are centered within the scope of our mORMot server, we implemented in the ORM an integrated mean of tracking changes (aka Audit Trail) of any TSQLRecord.
In short, our ORM is transformed into a time-machine, just like the good old DeLorean!

Keeping a track of the history of business objects is one very common need for software modeling, and a must-have for any accurate data modeling, like Domain-Driven Design.
By default, as expected by the OOP model, any change to an object will forget any previous state of this object. But thanks to mORMot's exclusive change-tracking feature, you can persist the history of your objects.

Enabling audit-trail

By default, change-tracking feature will be disabled, saving performance and disk use.
But you can enable change tracking for any class, by calling the following method, on server side:

 aServer.TrackChanges([TSQLInvoice]);

This single line will let aServer: TSQLRestServer monitor all CRUD operations, and store all changes of the TSQLInvoice table within a TSQLRecordHistory table.

Continue reading...

2014, Friday February 28

Are NoSQL databases ACID?

One of the main features you may miss when discovering NoSQL ("Not-Only SQL"?) databases, coming from a RDBMS background, is ACID.

ACID (Atomicity, Consistency, Isolation, Durability) is a set of properties that guarantee that database transactions are processed reliably. In the context of databases, a single logical operation on the data is called a transaction. For example, a transfer of funds from one bank account to another, even involving multiple changes such as debiting one account and crediting another, is a single transaction. (Wikipedia)

But are there any ACID NoSQL database?

Please ensure you read the Martin Fowler introduction about NoSQL databases.
And the corresponding video.

First of all, we can distinguish two types of NoSQL databases:

  1. Aggregate-oriented databases;
  2. Graph-oriented databases (e.g. Neo4J).

By design, most Graph-oriented databases are ACID!
This is a first good point.

Then, what about the other type?
In Aggregate-oriented databases, we can identify three sub-types:

  • Document-based NoSQL databases (e.g. MongoDB, CouchDB);
  • Key/Value NoSQL databases (e.g. Redis);
  • Column family NoSQL databases (e.g. Cassandra).
Whatever document/key/column oriented they are, they all use some kind of document storage.
It may be schema-less, blob-stored, column-driven, but it is always some set of values bound together to be persisted.
This set of values define a particular state of one entity, in a given model.
Which we may call Aggregate.

Continue reading...

2014, Saturday January 4

Domain-Driven Design: part 4

One year ago, we already made a quick presentation of Domain-Driven Design, in the context of our mORMot framework.
After one year of real-world application of those patterns, it is now time to give more light to DDD.

Let's continue with part 4, which will define Domain-Driven Design as could be implemented with our Synopse mORMot framework

Continue reading...

Domain-Driven Design: part 3

One year ago, we already made a quick presentation of Domain-Driven Design, in the context of our mORMot framework.
After one year of real-world application of those patterns, it is now time to give more light to DDD.

Let's continue with part 3, which will define Domain-Driven Design patterns and principles - this will be the main article of the whole serie!

Continue reading...

Domain-Driven Design: part 2

One year ago, we already made a quick presentation of Domain-Driven Design, in the context of our mORMot framework.
After one year of real-world application of those patterns, it is now time to give more light to DDD.

Let's continue with part 2, which will define Domain-Driven Design high-level model principles.

Continue reading...

Domain-Driven Design: part 1

One year ago, we already made a quick presentation of Domain-Driven Design, in the context of our mORMot framework.
After one year of real-world application of those patterns, and a training made by a great French software designer named Jérémie Grodziski, it is now time to give more light to DDD.

Let's start with part 1, which will be a general introduction to Domain-Driven Design, trying to state how it may be interesting (or not) for your projects.

Continue reading...

2013, Sunday January 20

Adding JavaScript server-side support to mORMot

A long-time mORMot user and contributor just made a proposal on our forums.
He did use mORMot classes to integrate a SpiderMonkey JavaScript engine to our very fast and scaling HTTP server, including our optimized JSON serialization layer.

Today, he sent to me some of his source code, which sounds ready to be included in the main trunk!

This is a great contribution, and Pavel's goal is nothing less than offering
Delphi based, FAST multithreaded server with ORM and node.js modules compatible.

Continue reading...

2013, Saturday January 5

Domain-Driven-Design and mORMot

Implementing Domain-Driven-Design (DDD) is one goal of our mORMot framework.

We already presented this particular n-Tier architecture.

It is now time to enter deeper into the material, provide some definition and reference.
You can also search the web for reference, or look at the official web site.
A general presentation of the corresponding concepts, in the .NET world, was used as reference of this blog entry.

Stay tuned, and ride the mORMot!

Continue reading...