dictionaryadapter-customize-keys.md

Castle DictionaryAdapter - Customizing Adapter Keys

By default DictionaryAdapter will use very simple strategy when inserting/retrieving data to/from dictionary via adapter - property name becomes the key.

So doing:

adapter.Name = "Stefan";

is identical to doing

dictionary["Name"] = "Stefan";

Same with reading

var name = adapter.Name;

is identical to doing

var name = (string)dictionary["Name"];

ℹ️ A word about conversion: Well that's not entirely true. DictionaryAdapter uses a more sophisticated mechanism for conversion than just plain casting.

This is a fine default, but the adapter lets you customize that behavior using attributes.

For the examples below, lets assume the setup is as follows:

var dictionary = new Hashtable();
var adapter = new DictionaryAdapterFactory.GetAdapter<IPerson>(dictionary);

Standard Attributes

Out of the box DictionaryAdapter provides set of attributes that should suffice for majority of cases.

Key Attribute

If you want the property name and dictionary key to be totally unrelated you can override the default name using KeyAttribute.

public interface IPerson
{
   [Key("PersonId")]
   string Name {get; set;}
}

Now:

adapter.Name == dictionary["PersonId"];

KeyPrefix Attribute

If you would like to prefix all keys in dictionary with some string use KeyPrefixAttribute.

[KeyPrefix("Person")]
public interface IPerson
{
   string Name {get; set;}
}

Now:

adapter.Name == dictionary["PersonName"];

If we had more properties on the interface, they'd all get prefixed.

TypeKeyPrefix Attribute

If you would like to prefix all keys in dictionary with full name of the interface use TypeKeyPrefixAttribute. This is especially useful when you have multiple adapters over common dictionary and you want to avoid one overriding another.

namespace Acme.Crm;

[TypeKeyPrefix]
public interface IPerson
{
   string Name {get; set;}
}

Now:

adapter.Name == dictionary["Acme.Crm.IPerson#Name"];

If we had more properties on the interface, they'd all get prefixed.

KeySubstitution Attribute

If you would like to replace certain characters in your key use TypeKeyPrefixAttribute. This is especially useful when you want to use certain characters in your key, that are not legal in C# names. You can set the attribute at interface level, or at property level.

public interface IPerson
{
   [KeySubstitution("_",".")]
   string Full_Name {get; set;}
}

Now:

adapter.Full_Name == dictionary["Full.Name"];

Creating Custom Attributes

Custom attributes need to implement two interfaces:

• IDictionaryBehavior - Standard base type for all DictionaryAdapter attributes. Usually you'll inherit base DictionaryBehaviorAttribute class and forget about it.
• IDictionaryKeyBuilder - that's the contract for customizing the key.

Example - KeyPostfix Attribute

As an example let's assume we want to create attribute that adds common postfix to the property keys, so that we can use it like follows:

public interface IPerson
{
   [KeyPostfix("Person")]
   string Name {get; set;}
}

and get:

adapter.Name == dictionary["NamePerson"];

Simple implementation might look like this:

[AttributeUsage(AttributeTargets.Property, AllowMultiple = false, Inherited = true)]
public class KeyPostfixAttribute : DictionaryBehaviorAttribute, IDictionaryKeyBuilder
{
	private String postfix;

	public KeyPrefixAttribute(string keyPrefix)
	{
		this.postfix = keyPrefix;
	}

	String IDictionaryKeyBuilder.GetKey(IDictionaryAdapter dictionaryAdapter, String key, PropertyDescriptor property)
	{
		return key + postfix;
	}
}