Application Generation using AjGenesis
Filed under: .NET, ASP.NET, AjGenesis, C Sharp, Code Generation, Domain-Driven Design, Java, Programming, Visual Basic .NET |
Comments(3) These days, I wrote new examples for my open source project AjGenesis
http://www.ajlopez.com/ajgenesis
http://www.codeplex.com/ajgenesis
Using AjGenesis, we can produce, starting from our own model, applications for ASP.NET 1.x/2.x, JSP, using SQL Server in .NET, with ADO.NET or NHibernate, or MySql with Java and Hibernate. The sample generated applications use a layered architecture (but remember: these are sample applications, you can write and use your own models, tasks, and templates). Other option: it can generate layers following ideas from Eric Evans’ Domain-Driven Design.
I’m still writing those examples, but now, you can download the current version from
The examples require the use of AjGenesis last release:
but you can try the current version under development:
In this post, I want to comment how AjGenesis works and some of its inner structure, using one of those examples. Although I will concentrate in producing VB.NET code, you’ll find that the example is able to produce C Sharp and Java/JSP solutions, as well.
First, let’s review first some points about the project. The big picture:
AjGenesis Version 0.4.3 is written using VB.NET V1.x, but version 0.5 is the current version under development, and it was rebuilt using .NET 2.0. The project is open source, and has a BSD-like license, that allows to use it in any project what you want: you only need to comply with the license (in short, put some reference to the original project). It is possible to be used like a library, invoked from your own project, or it is possible to be invoked from command line, or even it can be used from using NAnt (this tool gives you a better organization of the code generation tasks).
There are several samples in the page of the project (inside the project zip source file and in additional files). They generate code from a model, invoking tasks and processing templates. The samples generate code PHP, Java, JSP, VB.NET, C#, ASP.NET, and even scripts of procedure and data base stored. I want to emphasize two points:
- The model to use is totally definible by you. It’s a free model, it’s not a fixed one. You can model what you want to model.
- The tasks and templates to apply are totally programmable and controlable. You are in charge.
That’s make a difference from other generators. We can create our own model, and its own templates and tasks, to generate any text artifacts. Other systems start from the data base, and they only generate a group of predefined text files (as POJOs, plain old java objects, or DAOs, Data Objects Access). But with AjGenesis you can generate any text file you need.
In order to better understandind the free model concept, read a previous post:
Generating Code Hello World with AjGenesis
In that post, the initial steps are described, using a free model, totally oriented to the domain to represent: a typical Hello World application, implemented in different technologies.
Creating an application
Let’s do something more complete in this post. Suppose we need to create a simple solution simple, with two tables, in a MS SQL Server databse, source code in VB.NET 2,0, web interface, layer of services, layer of data, business components and business entities a la Microsoft. We want to generate the solution, the projects, scripts for database creation, and stored procedures. This example is included in the examples AjGenesisExamples3New.zip. First step: to write the model.
The project
In a directory of projects of the examples that accompany this article, there is a Projects/AjFirstExample directory.
In that directory it is the Project.xml file that contains the model.
<Project> <Name>AjFirstExample</Name> <Description>First Example using AjGenesis</Description> <Prefix>AjFE</Prefix> <Domain>com.ajlopez</Domain> <CompanyName>ajlopez</CompanyName> <Model> <Entities> <Entity Source="Entities/Customer.xml"/> <Entity Source="Entities/Supplier.xml"/> </Entities> </Model> </Project>
Remember: the model is free. Here we define the templates that we are going to use. The model contains two simple entities: customers and suppliers.
The entities
The XML file is not terribly long: AjGenesis allows that any node of the model is specified apart in a file. This is a criterion that I have used to define how the model is written: the resulting XML does not have to hurt at sight, must be understandable and abarcable in a reading.
In the Project.xml, that feature is used in the case of the entities, with the Source attribute. Let us examine an entity, written in Entities/Customer.xml:
<Entity> <Name>Customer</Name> <Description>Customer Entity</Description> <SetName>Customers</SetName> <Descriptor>Customer</Descriptor> <SetDescriptor>Customers</SetDescriptor> <SqlTable>customers</SqlTable> <Properties> <Property> <Name>Id</Name> <Type>Id</Type> </Property> <Property> <Name>Name</Name> <Type>Text</Type> <SqlType>varchar(200)</SqlType> </Property> <Property> <Name>Address</Name> <Type>Text</Type> <SqlType>text</SqlType> </Property> <Property> <Name>Notes</Name> <Type>Text</Type> <SqlType>text</SqlType> </Property> </Properties> </Entity>
There are attributes of the entities, like its name and description, in plural and singular. This data serve to name them in the resulting pages, or within the code. The properties are the fields to maintain in each entity..
Aside from the entities, in another directory, Technologies, specifies the dependent model of the technology, like VbNet2:
The templates
The templates to use are at the Templates/VbNet2 directory:
They are the templates for generation of code VB.Net 2.0. Also we will find groups for C# 1/2, Vb.NET 1,2, Java (although I’m thinking to drop templates for .NET 1.x: I don’t see any reason to maintain these). There are templates to use Nhibernate, Hibernate, JSP, MySql, and concepts of Domain-Driven Design, too. Let’s review a template as an example, the one that generates the organization in Visual BASIC, EntityVb.tpl:
<# message "Generating Entity ${Entity.Name}" include "Templates/VbNet2/VbFunctions.tpl" include "Templates/VbNet2/Prologue.tpl" #> ' ' Project ${Project.Name} ' ${Project.Description} ' Entity ${Entity.Name} ' ${Entity.Description} ' ' Public Class ${Entity.Name} ' Private Fields <# for each Property in Entity.Properties message "Procesando Campo ${Property.Name}" #> Private m${Property.Name} as ${VbType(Property)} <# end for #> ' Default Constructor Public Sub New() End Sub ' Public Properties <# for each Property in Entity.Properties message "Procesando Propiedad ${Property.Name}" #> Public Property ${Property.Name}() as ${VbType(Property)} Get Return m${Property.Name} End Get Set(ByVal Value As ${VbType(Property)}) m${Property.Name} = Value End Set End Property <# end for #> End Class
Like before, control structures are used. XML is the serialized format of the model. During the code generation process, the model is loaded in memory, ready to be accesible via dynamic variables.
The steps
We have more files to generate: from the pages ASPX, and their associated code, the projects of facade on watch, organizations, access to data, the file of solution, and more. In order to automate this generation, the example has several files of tasks, in the Tasks directory, where the steps are described to execute. There are two great tasks: the steps to execute independently of the chosen technology, like completing the model, reviewing it, and the employees of the technology, like generating such file JSP or ASPX, depending on if we want Java or .NET.
The task of completing the model is in charge of Tasks\BuildProject.ajg, that begins with:
' ' Build Project ' Complete the Project Data ' Project must be loaded in global variable Project ' PrintLine "Completing Project ${Project.Name}" include "Templates/EntityFunctions.tpl" include "Templates/Utilities.tpl" if not Project.Title then Project.Title = Project.Name end if if not Project.Version then Project.Version = "1.0.*" end if if not Project.SystemName then Project.SystemName = Project.Name end if
The template includes some auxiliary functions, and then, it begins to complete the model that resides in the Project variable. For example: if the project lacks Project.Title the program set Project.Name as Project.Title. The program continues:
for each Entity in Project.Model.Entities PrintLine "Entity " + Entity.Name for each Property in Entity.Properties PrintLine "Property " & Property.Name if Property.Type="Id" and not Property.SqlType then Property.SqlType="int" end if if Property.SqlType and not Property.SqlColumn then Property.SqlColumn = Property.Name end if if Property.Type="Id" and not Entity.IdProperty then Entity.IdProperty = Property end if if Property.Reference then ...
After that process, the technology tasks are executed. The example use Tasks\BuildVbNet2.ajg, here a fragment:
<# include "Templates/Utilities.tpl" include "Templates/VbNet2/UtilitiesVb.tpl" message "Creating Directories..." FileManager.CreateDirectory(Project.BuildDir) FileManager.CreateDirectory("${Project.BuildDir}/Sql") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.Entities") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.Entities/My Project") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.Data") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.Data/My Project") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.Services") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.Services/My Project") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.Business") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.Business/My Project") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.WebClient") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.WebClient/App_Themes") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.WebClient/App_Themes/Default") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.WebClient/Admin") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.WebClient/Controls") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.WebClient/MasterPages") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.WebServices") FileManager.CreateDirectory("${Project.BuildDir}/Src/${Project.Name}.RemoteServices") message "Defining Solution and Projects..." ...
In this fragment, the directories necessary are created to lodge the solution. The name of the directory is extracted of the model from Project.BuildDir. Note that ${ } in a string is used to expand the inside expression into the string value.
Technology Model
Under the directory Project\AjFirstExample\Technologies they are some models that describes the technology parameters to use:
Let’s examine VbNet2.xml:
<Technology> <Programming> <Dialect>VbNet2</Dialect> </Programming> <Database> <Dialect>MsSql</Dialect> <Name>AjFirstExample</Name> <Username>sa</Username> <Prefix>ajfe_</Prefix> <Host>(local)</Host> </Database> </Technology>
These data is used during the template generation phase. It indicates the language, and the database to use.
Generating the solution
We could send the tasks from the command line, but we have a .build file for Nant, one for each technology to generate. We execute the tasks build, buildsql, and deploysql of AjFirstExampleVbNet2.build with the command line:
nant -buildfile:AjFirstExampleVbNet2.build build buildsql
(You must adjust the line
<property name=”ajgenesis.dir” value=”…./AjGenesis-0.5″/>
to reflect your AjGenesis installation directory)
Note the following lines in the build file:
<target name="loadtasks" description="loads AjGenesis tasks"> <loadtasks assembly="${nanttasks.dir}/AjGenesis.NAnt.dll" /> </target> <target name="init" depends="loadtasks" description="init the AjGenesis model, create build directory"> <mkdir dir="${build.dir}"/> <loadmodel model="${project.dir}/Project.xml"/> <loadmodel model="${project.dir}/Technologies/${technology}.xml"/> <executetask task="${tasks.dir}/BuildProject.ajg"/> <executetask task="${tasks.dir}/BuildTechnology.ajg"/> </target>
These tasks load an AjGenesis NAnt tasks, load the models, and execute the tasks.
In the Build/AjFirstExample/VbNet2/Sql directory they are left scripts of creation of the base and stored procedures. And in the directory Src brother, surprise! We’ll have the generated solution:
There were generated several projects, into a solution. We can load the solution into the Visual Studio 2005:
Using another NAnt file, AjFirstExampleCSharp2.build, we can generate the same solution in CSharp:
You will find other projects and examples of .build files, that generate solutions using NHibernate, Hibernate use, JSP, and concepts of Domain-Driven Desing a la Eric Evans.
Reflections
Sure, everything cannot be generated automatically. It is important to remember always that fact. But in the day to day, we recognize that we have amount of repetitive text, tasks that we can well delegate to software.
A key point: the model in AjGenesis is free. The presented examples are only examples: we can general the model that we want, and to write the templates we need. It is important to write the templates so that the generated code is similar to what we had manually generated. If we don’t feel comfortable with the generated code, if it does not have our style, our experience, we’ll end up generating something that we do not understand.
Another thinking: the model must be independent of the technology. In the final example, we have seen how, from the same model, we can generate solutions for VB.NET, CSharp and other technologies.
Software can help us to generate software. More: it MUST help us. Our experience counts: what we learned to make applications, we can overturn it in this species of expert system, code generation tools. In the future, I hope to be able to incorporate to the project, in the templates and tasks, more decision making: as well as we gain experience in writing of applications, we can incorporate our accumulated knowledge on patterns, architecture and styles of programming.
And as it is an open source project, AjGenesis allows us extend it, to our taste and necessity.
Suggestions, use case stories, comments are welcome. You can write as comments to this post, or write directly to me. Thanks to all that tested and adopted this project, and helped me to write it.
Angel “Java” Lopez
http://www.ajlopez.com/en
InfoQ has published a mini-book (printed version with cost, free pdf to download), that is a summary of DDD, and of Eric Evan’s book on DDD.