Archive for the ‘Spring.Net’ Category

Using attributes with Spring.NET to configure your application

Friday, April 24th, 2009

When using Spring.Net you end up editing xml files to wire everything together. While something like fluent Spring.Net would be very nice to have, some of the xml authoring can be solved by using attributes. As sample I’ll use a real life example where I implemented it.

I had to add reporting to an application which consists of different modules. Depending on the license of the user he’d have a contacts module, a document management module, tasks, etc. The user would select the contents of his report and then fire up the designers to choose fields, order or group them, etc.

The end-user components we use are quite powerful so I only had to find a way to get the content into the report component as a dataset. Normally I keep away from using datasets but in this case it’s allowed. Note that I’m not using data adapters and other stuff, I just transform my rich object model into a flat dataset.

Each module writes an entitymapper for all of the entities that can be used as reporting source.

[EntityMapper(EntityType = typeof(ContactDto))]
public class ContactMapper
    : EntityMapper
{
    public override DataSet MapToDataSet(IEnumerable<ContactDto> entities)
    {
        DataSet dataSet = new DataSet();
        //fill with data
        return dataSet;
    }
}

I only wanted to add the object definition to the configuration specific for this module. I didn’t want to edit the config for reporting module. It should just pick all the mappers up and use them when entities of that type are handed to it.

The solution for this is using an IObjectPostProcessor to inspect everything that is configured in your container and do some additional logic.

public class MapperPostProcessor
    : IObjectPostProcessor
{
    private readonly Type attributeType;
 
    public MapperPostProcessor()
    {
        attributeType = typeof (EntityMapperAttribute);
    }
 
    public DataSetMapper Mapper
    {
        get;
        set;
    }
 
    #region IObjectPostProcessor Members
 
    public object PostProcessAfterInitialization(object instance, string objectName)
    {
        object[] o = instance.GetType().GetCustomAttributes(attributeType, true);
        if(o.Length == 1)
        {
            var attribute = o[0] as EntityMapperAttribute;
            var entityMapper = instance as IEntityReportMapper;
            Mapper.RegisterMapper(entityMapper, attribute.EntityType);
        }
        return instance;
    }
 
    public object PostProcessBeforeInitialization(object instance, string name)
    {
        return instance;
    }
 
    #endregion
}

Any postprocessor in your Spring context is automatically picked up by Spring and the methods will be called on the appropriate time. In this implementation I check every instance that is handed to the PostProcessAfterInitialization method for my own attribute, if it’s present I register it to my mapper manager for the specified type. For more info about this you should check out the documentation.

Out of the box Spring.NET has some of these already for you. For instance you can put the [Required] attribute on the properties that need to have a value after they have been constructed. If at that time they haven’t been initialized you’ll get an exception.

AdventureWorks++

Thursday, February 7th, 2008

In a series of posts I (and those interested in joining me) will create an application using Spring.Net and NHibernate as supporting frameworks. Why do I start with this? Because there are a lot of examples out there that don’t go beyond the ‘Hello World’ sample and while everybody is talking about how things should be done, a real-life enterprise ready solution is not available. Don’t get me wrong here, I’m not saying I have the solution for every problem. I just hope that everybody will be able to learn something, including me! One of the key goals will be to use domain-driven design to drive the development backed up with user stories, unit tests, continuous integration,…

I can only give a rough outline of the application for now. It will consist of a web and windows front. These front-ends will communicate via webservices with the back-end powering the business. The AdventureWorks Microsoft sample will be used as the customer who needs to modernize its infrastructure.

 That’s all for now, a lot more to come.